ACT4910QW
Rev 3.0, 17-Jul-2018
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TM
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1
36V Buck/Boost
Controller
Caps
Health Monitor/
ADC
Input2.7V‐18V
Blockingupto24V 2.7V‐18V
5V-36V
40mΩ
FET
25mΩ
FET
PMU
System
Core/Flash
5V-36V
eFuse 17mΩ
Inrush Controller
Power Loss Protection with 6A eFuse
BENEFITS and FEATURES
Wide 2.7-to-18V Operating Input Range
24V Max Input Blocking Voltage
Adjustable Bus Voltage Start-Up Slew Rate for In-
rush Current Control
Configurable Input power Failure Level
Programmable up to 10A Input Current Limit
Programmable 5V to 36V Boost Storage Voltage
36V@6A Synchronous Buck Supports 100% Duty
Cycle
Programmable up to 1.13MHz Buck Operating Fre-
quency for Small Inductor Size
Undetectable Transition from Input Supply to Ca-
pacitor Bank Power
Compatible with Different Types of Storage Caps:
Super Caps, Electrolytic, Tantalum, POSCAP
etc.
ADC Monitoring of Critical Signals
Autonomous Health Monitoring for Detection of
Earlier Storage Capacitor Failures
Configurable Interrupts to Inform Host for any
Faults/Status Change
eFuse, Boost, and Buck UV/OV/OC Protection
Thermal Alert and Protection
Thermal Enhanced FCQFN 5x5-28 package
APPLICATIONS
Solid State Drives
Industrial Applications
Backup Power
Hot Plug Devices
GENERAL DESCRIPTION
The ACT4910 device is a highly integrated power loss
protection IC. It provides backup storage power in the
event of an input power failure. A built-in boost
converter provides high voltage energy storage to
minimize storage capacitor size requirements. The
built-in buck converter regulates the storage voltage to
a fixed output voltage. It contains internal, back-to-
back eFuse FETs to provide bi-directional input to
output isolation. The IC also provides hot swap and
inrush current control.
The ACT4910 is very flexible and can easily be
configured with I
2
C and external components. It
features programmable storage capacitor voltage to
optimize the storage capacitor sizing and system run
time. The internal ADC and health monitoring provide
an extra layer of protection and improve system
reliability and early capacitor failure notification. It
automatically checks the storage capacitor health and
notifies the user when the energy in the storage caps
is not sufficient for backup power. The ADC also
measures the input voltage, output voltage, storage
voltage, eFuse current, and die temperature. The built-
in synchronous buck converter maximizes energy
transfer from the storage caps to the system.
ACT4910 provides an I
2
C bus interface to allow MCU
control and monitoring. There are supervisor monitors
for the input voltage, output voltage, and storage
voltage. It is available with the thermal enhanced QFN
5x5 28 pins package.
ACT4910QW
Rev 3.0, 17-Jul-2018
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FUNCTIONAL BLOCK DIAGRAM
VREF
VOUTVIN
SCL
SDA
HSB
BSET
SW
STR
FB
COMP
ISET
BlockFET
Controller
Buck/Boost
Controller
SS
nIRQ
PLI REF
VSS
Main
Controller
EN PGND
Health
Monitor
Q
LS_BOOST
Q
HS
Q
LS_BUCK
EN_OV_REF
0.64V
Q
BLOCK1
Q
BLOCK2
ACT4910QW
Rev 3.0, 17-Jul-2018
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ORDERING INFORMATION
PART NUMBER Input
Voltage
Storage
Voltage
Fsw PLI Function 7 Bit I
2
C
Address
PACKAGE
ACT4910QW121-T 12V 28V 1130kHz PLI & VOUT OK 0x5Ah
FCQFN5x5-28
ACT4910QW122-T 12V 36V 900kHz PLI & VOUT OK 0x5Ah
FCQFN5x5-28
ACT4910QW123-T 12V 27V 900kHz PLI & VOUT OK 0x5Ah
FCQFN5x5-28
ACT4910QW302-T 3.3V 27V 560kHz PLI & VOUT OK 0x5Ah
FCQFN5x5-28
ACT4910QWxxx-T
CMI Option
Pin Count
Package Code
Product Number
Tape and Reel
Note 1: Standard product options are identified in this table. Contact factory for custom options, minimum order quantity required.
Note 2: All Active-Semi components are RoHS Compliant and with Pb-free plating unless specified differently. The term Pb-free means semiconductor
products that are in compliance with current RoHS (Restriction of Hazardous Substances) standards.
Note 3: Package Code designator “Q” represents QFN
Note 4: Pin Count designator “W” represents 28 pins
Note 5: Refer to the CMI Options section at the end of the DS for more information on each CMI version.
ACT4910QW
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PIN CONFIGURATION
ISET
STR
nIRQ
FB
VOUT
REF
PGND
VOUT
VOUT
SW
PLI
VOUT
BSET
VSS
HSB
PGND
COMP
VIN
SCL
SDA
VIN
VIN
VIN
EN
SS
VOUT
4
3
2
1
7
6
5
1098 14
15
16
17
28 27 26
11 12 13
25 24 23 22
18
19
20
21
VIN
VOUT
Figure 1: Pin Configuration – Top View – QFN5x5-28
ACT4910QW
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PIN DESCRIPTIONS
PIN NAME DESCRIPTION
1
HSB
High Side Bias, Boot-strap pin. This provides power to the internal high-side
MOSFET gate driver circuitry. Connect a 47nF capacitor from HSB pin to SW pin
2
PLI
Power Loss Indicator Open-Drain Output. PLI goes low to indicate loss of input
power. Can also be configured as a storage voltage monitor or an output voltage
monitor. PLI is referenced to VSS.
3, 28
PGND
Power Ground. Connect to large ground plane on PCB
4
BSET
Sets the storage capacitor voltage. Place a resistor from BSET to VSS to set the
desired voltage.
5
REF
5V Internal Bias Voltage Output. Connect a 1µF capacitor between REF and VSS.
REF is for internal use only. Do not connect any circuitry to REF.
6
COMP
Compensation input pin for the buck converter.
7
FB
Output Voltage Feedback. Kelvin connect FB to the output capacitor.
8
VSS
Analog Ground. Kelvin connect VSS to the PGND plane.
9
SCL
I
2
C Clock Input. Needs an external pull up resistor.
10
SDA
I
2
C Data Input and Output. Needs an external pull up resistor.
11,12,13,2
3, 24, 25
VOUT
Output for by-pass mode, in-rush, and eFuse functionality. Connect VOUT to the
system load.
14
nIRQ
Interrupt Open-Drain Output. nIRQ goes low to indicate a fault condition. nIRQ is
referenced to VSS.
15
ISET
Input and Output Current Limit pin. ISET can also indicate the load current through
the eFuse. Connect a resistor from ISET to VSS to set the current limit.
16
SS
Soft Start Input. Place a capacitor from SS to VSS to control the eFuse startup
voltage slew rate.
17
EN
Enable Input. A dual comparator on EN measures the input voltage to determine if
it is under, voltage, over voltage, or within normal operating limits. Connect a
resistive voltage divider between VIN, EN, and VSS to set the EN_UV and EN_UV
thresholds. The EN_UV threshold is 0.64V. The EN_OV threshold is typically
0.92V, but can be modified by the IC’s CMI.
18,19, 20,
21, 22
VIN
Power Supply Input. Input to the eFuse. Connect a 0.1µF capacitor between VIN
and PGND as close to the IC as possible.
26
STR
Storage Capacitor Input. Connect the storage capacitors to STR. STR requires a
minimum capacitor of 100µF to PGND.
27
SW
Switching Pin. This is the boost converter switch node and the buck converter
switch node. Connect the inductor to SW.
ACT4910QW
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ABSOLUTE MAXIMUM RATINGS
PARAMETER VALUE UNIT
FB, SS, ISET, REF, SDA, SCL, EN, BSET, nIRQ to VSS -0.3 to 6 V
VIN, VOUT to PGND (ACT4910) -0.3 to 24 V
HSB to SW -0.3 to 6 V
SW to PGND -0.3 to STR+ 0.3 V
PLI to VSS -0.3 to 24 V
STR to PGND -0.3 to 40 V
VSS to PGND -0.3 to + 0.3 V
ESD Rating (human body model), all pins 2 kV
Junction to Ambient Thermal Resistance, dependent on board layout 16.8 °C /W
Operating Ambient Temperature Range (T
A
) -40 to 105 °C
Operating Junction Temperature (TJ), (note 1) -40 to 125 °C
Storage Temperature -40 to 150 °C
Lead Temperature (Soldering 10s) 300 °C
Note1: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect
device reliability.
Note2: Measured on Active-Semi Evaluation Kit
ACT4910QW
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SYSTEM CHARACTERISTICS
(VIN = 12V, T
A
= 25°C, unless otherwise specified)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Input Supply
Input Supply Voltage Range VIN 2.7 18 V
Input Supply Power On Reset (Internal) VIN Rising 2.53 V
Input Supply Power On Reset
Hysteresis (Internal POR) VIN Falling 90 mV
Input Supply Over Voltage Lock Out
(OVLO) 20 V
Input Under Voltage Lock Out (UVLO) VIN Rising (Boost/eFuse Enabled) 2.65 2.7 V
Input UVLO Hysteresis VIN Falling 50 mV
Input Operation Current
eFuse Enabled and Soft start completed
Buck/Storage Regulator Disabled
ADC Disabled
Storage Health Check Disabled
3 mA
eFuse Enabled and Soft start completed
Buck/Storage Regulator Disabled
ADC Enabled
Storage Health Check Disabled
5.5 mA
Input Current (Shutdown) V
EN
=0V 470 µA
Thermal
Thermal Warning Sets nIRQ 120 °C
Thermal Shutdown – Disables buck and
boost 145 °C
Thermal Shutdown – Disables eFuse 155 °C
Thermal Comparators Hysteresis 15 °C
SET Thresholds
BSET Current Source BSET = 1.0V (25°C) 19.6 20 20.4 µA
BSET Current Source Temperature
Coefficient BSET = 1.0V (25°C – 125°C) 0.011 %/°C
STR Thresholds
Input Under Voltage Lock Out
(STR_UVLO) STR Falling 3.6 V
Input Under Voltage Lock Out
(STR_UVLO) STR Rising 4.0 V
ACT4910QW
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PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Open Drain Outputs
Switch Maximum Voltage Range
(nIRQ,PG_STR, SDA) 0 5 V
Switch resistance (nIRQ,PG_STR, SDA) Sinking Current 500µA 100 Ω
Enable Thresholds
Under Voltage Reference UV REF after POR release (-40°C ~ 125°C) 0.63 0.64 0.65 V
Overvoltage Reference Programmable
Range OV REF after POR release 0.92 V
EN Deglitch Time EN UV Rising or OV Falling (0ms turn-on delay) 1 ms
Hysteresis for Reference 17 mV
ACT4910QW
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INTERNAL BUCK REGULATOR
(VIN = 12V, T
A
= 25°C, unless otherwise specified)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Operating Input Voltage Range 4.2 36 V
Typical Output Voltage 3.3 V
Programmable Output Voltage Range Using external resistor divider 1.8 18 V
Standby Supply Current V
OUT
= 103%, Regulator Enabled, No Load, not switch-
ing 500 µA
Feedback Voltage 1.2 V
Output Voltage Accuracy V
OUT
= 12V, I
OUT
= 2A (PWM mode) -1% V
NOM
1% V
Output Voltage Accuracy V
OUT
= 12V, I
OUT
= 1mA (PFM mode) -1% V
NOM
1% V
Line Regulation V
OUT
= 12V V
IN
= 5.5V to 12V, PWM Regulation 0.02 %/V
Load Regulation V
OUT
= 12V PWM Regulation 0.04 %/A
Power Good Threshold V
OUT
Rising 90.5 93 95.5 %V
NOM
Power Good Hysteresis V
OUT
Falling 3 %V
NOM
Overvoltage Fault Threshold V
OUT
Rising 107 110 113 %V
NOM
Overvoltage Fault Hysteresis V
OUT
Falling 2 %V
NOM
Programmable Switching Frequency
Range 320 1130 kHz
Current Limit, Cycle-by-Cycle
BK_CLIM = 00
BK_CLIM = 01
BK_CLIM = 10
BK_CLIM = 11
5.0
6.0
7.0
9.0
A
Current Limit, Cycle-by-Cycle Tolerance
At default BK_CLIM -10% +10%
At other set points -15% +15%
Current Limit, Shutdown Above BK_CLIM +15% +22.5% +30%
High Side On-Resistance I
SW
= -3A, V
STR
= 12V 45 mΩ
Low Side On-Resistance I
SW
= 3A, V
STR
= 12V 28 mΩ
SW Leakage Current V
STR
= 12V, V
SW
= 0 or 5.5V 1 µA
ACT4910QW
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INTERNAL EFUSE
(VIN = 12V, T
A
= 25°C, unless otherwise specified)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Normal Mode
Operating Voltage Range 2.7 18 V
eFuse On-Resistance
I
SW
= -2A, VIN= 3.3V, 5V, and 12V, T
J
= 25°C 17 mΩ
I
SW
= -2A, VIN= 3.3V, 5V, and 12V, T
J
= 100°C 24.5 mΩ
Programmable eFuse Current Limit
Range
VIN = 12V, Configured using ISET pin, Triggers nIRQ Pin 1 10 A
VIN = 3.3V, Configured using ISET pin, Triggers nIRQ
Pin 1 7 A
Internal Path Current Regulation Accuracy V
ISET
1 V
ISET Monitor Current Ratio ISET current divided by eFuse current 1/50,000
eFuse Overcurrent Detection Deglitch 10 µs
eFuse Overcurrent Current Shutdown
11 A
Current Limit Restart Time 100 ms
eFuse Soft start C
SS
= 10nF 5.94 6.6 7.26 mV/us
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STORAGE BOOST REGULATOR
(VIN = 12V, T
A
= 25°C, unless otherwise specified)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
Storage Boost Converter
Operating Voltage Range 2.7 36 V
Programmable Output Voltage Range 5.0 36 V
Peak switching Current
BST _CLIM = 00
BST _CLIM = 01
BST _CLIM = 10
BST _CLIM = 11
250
650
950
1500
mA
Standby Supply Current V
STR
= 103%, Regulator Enabled, not switching 25 40 µA
Output Voltage Accuracy V
STR
= 28V, I
OUT
= 15mA (continuous PWM mode) -3% V
NOM
3% V
Power Good Threshold V
STR
Rising 95 %V
NOM
Power Good Hysteresis V
STR
Falling 2 5 %V
NOM
Overvoltage Fault Threshold V
STR
Rising 110 %V
NOM
Overvoltage Fault Hysteresis V
STR
Falling 3 %V
NOM
Minimum On-Time 50 ns
Low Side FET On-Resistance I
SW
= 325mA 300 mΩ
ACT4910QW
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HEALTH MONITOR
(VIN = 12V, T
A
= 25°C, unless otherwise specified)
PARAMETER CONDITIONS MIN TYP MAX UNIT
Health Monitor
Operating Voltage Range 4.2 40 V
Sink Current Source 9 10 11 mA
Programmable Health Monitor Current
Sink Timer Range 2 1280 ms
Programmable Storage Voltage Threshold
Range Configurable 0.2% steps 95 98 %
ADC Monitoring
Operating Voltage Range 3 20 V
Supply Current Enabled 2 5 mA
Total Error 5V scale and 8 bit range 0.5 LSB
Conversion Time Total time for all channels 100 ms
Full Scale Input Range -2.5 2.5 V
Input Resistance 10 kΩ
Input Capacitance 5 pF
ACT4910QW
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I
2
C INTERFACE ELECTRICAL CHARACTERISTICS
(VIN = 5V, T
A
= 25°C, unless otherwise specified.)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
SCL, SDA Input Low V
IO
= 1.8V 0.6 V
SCL, SDA Input High V
IO
= 1.8V 1.2 V
SDA Leakage Current SDA=5V 1 µA
SDA Output Low I
OL
= 5mA 0.35 V
SCL Clock Frequency, f
SCL
0 1000 kHz
SCL Low Period, t
LOW
0.5 µs
SCL High Period, t
HIGH
0.26 µs
SDA Data Setup Time, t
SU
50 ns
SDA Data Hold Time, t
HD
(Note1) 0 ns
Start Setup Time, t
ST
For Start Condition 260 ns
Stop Setup Time, t
SP
For Stop Condition 260 ns
Capacitance on SCL or SDA Pin 10 pF
SDA Rise Time SDA, T
r
Device requirement 120 ns
SDA Fall Time SDA, T
f
Device requirement 120 ns
Pulse Width of spikes must be suppressed
on SCL and SDA 0 50 ns
Note1: Comply with I
2
C timings for 1MHz operation - “Fast Mode Plus”.
Note2: No internal timeout for I
2
C operations, however, I
2
C communication state machine will be reset when entering UV/POR State.
Note3: This is an I
2
C system specification only. Rise and fall time of SCL & SDA not controlled by the device.
Note4: Device Address is factory configurable to 7’h1A, 7’h3A, 7’h5A.
Figure 2: I
2
C Data Transfer
SDA
SCL
tST tSU
tHD tSP
tSCL
Start
condition
Stop
condition
ACT4910QW
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FUNCTIONAL DESCRIPTION
General
ACT4910 provides protection, control, and supple-
mental storage for power failure prevention systems.
This functionality goes by many names: Power Loss
Protection (PLP), Power Loss Imminent (PLI) and
Power Failure Protection (PFP). It provides a system
with additional run time after a power failure to all the
system to save critical data before shutting down. Typi-
cal applications include solid state disk drives (SSD)
and servers. In normal operation when input power is
good, the IC connects the input to the output through
the eFuse. This powers the system load from the sys-
tem input power. If an input voltage fault occurs, the IC
disconnects the input from the output and enters sup-
plement mode, where output power comes from the
high voltage storage capacitor power. The internal buck
converter efficiently converts the storage voltage down
to the regulated output voltage. All startup, storage ca-
pacitor charging, and switching between normal and
supplement mode operation is autonomous and does
not require user intervention.
During start up, the ACT4910 limits the output voltage
dV/dt to minimize system level inrush currents. After
softstart is complete, the IC charges the storage capac-
itors with the internal boost converter. The IC automati-
cally recharges the storage capacitors as needed. The
IC contains extensive protection circuitry to protect
against input voltage overvoltage and undervoltage,
output voltage overload and short circuit, degraded stor-
age capacitors, and thermal overload.
The IC communicates with the host processor via I2C
and GPIOs. The nIRQ pin indicates general faults which
can be read by the host processor via I2C. A dedicated
power failure pin, PLI, automatically and immediately
goes low to indicate a power loss condition. This gives
the system advanced warning to complete all active
tasks and shutdown. See the Pin Function section for
additional PLI pin functionality.
The ACT4910 is highly flexible and contains many I2C
configurable functions. The IC’s default functionality is
defined by its default CMI (Code Matrix Index), but
much of this functionality can be changed via I2C. I2C
functionality includes storage voltage setting, OV and
UV fault thresholds, switching frequencies, ADC control
and automatic fault thresholds, PLI pin functionality,
health check settings, and current limits. The CMI Op-
tions section shows the default settings for each availa-
ble CMI option. Contact sales@active-semi.com for ad-
ditional information about other configurations.
I
2
C Serial Interface
To ensure compatibility with a wide range of systems,
the ACT4910 uses standard I
2
C commands. The
ACT4910 operates as a slave device, and can be fac-
tory configured to one of three 7-bit slave addresses.
The 7-bit slave address is followed by an eighth bit,
which indicates whether the transaction is a read-oper-
ation or a write-operation. Refer to each specific CMI for
the IC’s slave address
7-Bit Slave Address 8-Bit Write
Address
8-Bit Read
Address
0x1Ah 001 1010b 0x34h 0x35h
0x3Ah 011 1010b 0x74h 0x75h
0x5Ah 101 1010b 0xB4h 0xB5h
The I
2
C packet processing state machine does not have
a timeout function, however, any time the I
2
C state ma-
chine receives a start bit command, it immediately re-
sets the packet processing, even if it is in the middle of
a valid packet. The I
2
C functionality is operational in all
states except RESET.
I
2
C commands are communicated using the SCL and
SDA pins. SCL is the I
2
C serial clock input. SDA is the
data input and output. SDA is open drain and must have
a pull-up resistor. Signals on these pins must meet
timing requirements in the Electrical Characteristics
Table.
I
2
C Registers
The ACT4910 contains an array of internal registers that
contain the IC’s basic instructions for setting up the IC
configuration, output voltages, sequencing, fault
thresholds, fault masks, etc. These registers are what
give the IC its operating flexibility. The two types of
registers are described below.
Basic Volatile – These are R/W (Read and Write) and
RO (Read only). After the IC is powered, the user can
modify the R/W register values to change IC
functionality. Changes in functionality include things like
masking certain faults. The RO registers communicate
IC status such as fault conditions. Any changes to these
registers are lost when power is recycled. The default
values are fixed and cannot be changed by the factory
or the end user.
Basic Non-Volatile – These are R/W and RO. After the
IC is powered, the user can modify the R/W register
values to change IC functionality. Changes in
functionality include things like output voltage settings,
ACT4910QW
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startup delay time, and current limit thresholds. Any
changes to these registers are lost when power is
recycled. The default values can be modified at the
factory to optimize IC functionality for specific
applications. Please consult sales@active-semi.com for
custom options and minimum order quantities.
When modifying only certain bits within a register, take
care to not inadvertently change other bits.
Inadvertently changing register contents can lead to
unexpected device behavior.
State Machine
ACT4910 contains an internal state machine with seven
internal states: UV/POR, SOFT-START, NORMAL,
HEALTH CHECK, SUPPLEMENT, SHUTDOWN1, and
SHUTDOWN2.
UV/POR State
The IC enters the UV/POR state on power up. It also
enters UV/POR from SUPPLEMENT state in the
following conditions:
1. When the input voltage drops below the EN_UV
threshold.
2. When the storage capacitor voltage drops
below 3.6V.
3. When the buck converter output voltage goes
OV or UV.
The user may force the IC into UV/POR by writing a 1
into the FORCE_PWROFF bit, register 0x0Ah, bit 0.
When entering UV/POR from power up, all registers
reset to their default state. The registers retain their
existing values when the IC enters from SUPPLEMENT
state or from SHUTDOWN2 EFUSE. The IC transitions
to the SOFT-START state when EN pin is above 0.64V
and the input voltage is above UVLO.
SOFTSTART State
In the SOFTSTART state, the IC slowly turns on the
eFuse to minimize inrush currents. The output voltage
dV/dt ramp rate is controlled by the SS pin. The SS pin
directly controls the maximum output voltage dV/dt
while the ILIM pin indirectly controls it by limiting the
current into the output capacitance. The IC stays in the
SOFTSTART state until VIN-VOUT < 200mV and a
10ms timer times out. Note that the output voltage may
be fully charged up to VIN even though the IC in still in
the SOFTSTART state. The storage caps charge up to
the output voltage in this state.
NORMAL State
The NORMAL state is the normal operating state after
startup with no faults. The eFuse is fully on, VOUT =
VIN, and the IC provides full operating current. Note that
the IC charges the storage capacitors to their
programmed value at the beginning of NORMAL state.
HEALTH CHECK State
The HEALTH CHECK state can be considered a sub-
state of NORMAL. The IC operates identical to the
NORMAL state with the addition of activating the
circuitry that check the storage capacitor health. The IC
automatically enters HEALTH STATE every four
minutes. The user may also manually enter this state by
writing a 1 into the FORCE_HLTHCHK bit which is bit 1
in register 0x0Ah. This bit automatically resets to 0 after
the health check routine completes. The IC
automatically exits HEALTH CHECK and enters
SUPPLEMENT state in a fault condition.
SUPPLEMENT State
The IC enters SUPPLEMENT state when it detects a
fault condition. It opens the eFuse to bi-directionally
disconnect the input from the output. It automatically
turn on the buck converter to power the output from the
storage capacitors. The following five conditions move
the IC into SUPPLEMENT state.
1. EN voltage below UV threshold
2. EN voltage above the OV threshold
3. Input voltage above the OV threshold
4. eFuse current above the OC threshold
5. VIN – VOUT > 560mV
SHUTDOWN1 State
SHUTDOWN1 protects against over temperature
(145 °C), internal LDO failure, or boot capacitor failure.
The eFuse remains on and continues to provide power
to the output, but the boost converter is disabled. The
ADC remains on and I
2
C functionality is still operational.
The IC transitions to SHUTDOWN2 state if the die
temperature increases to 155°C. If transitions back to
the NORMAL state if the fault conditions go away.
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SHUTDOWN2 State
SHUTDOWN2 disables all IC functionality to protect
against extreme over temperature conditions above
155°C. This includes shutting off the eFuse. I
2
C
functionality not available in this state. The IC transitions
to SOFT-START when the junction temperature drops
and there is no overcurrent fault. Figure 3 shows the
ACT4910 State Diagram. Table 1 shows which
functions are enabled in each state. Note that the
current operating state can be determined by reading
the I
2
C register bits CURRENT_STATE in register
0x00h.
UV/POR
Soft‐
Start
Mode
VIN‐VOUT<200mV
Soft‐startdone
Supplement
Mode
Repeatevery4min
eFuseovercurrent
T
J
>155°C
Optional
Timer
12 5m s
EN>UV
&VIN>UVLO
eFusenotinOC
&T
J
<155°C
&100msdelay
eFuseovercurrent
T
J
>155°C
T
J
>135°C
LDOUV
StoragecapOV
Bootcapfail
Normal
Mode
Health
Check
Mode
StorageCap
isFilledto
PG_THR
Storagecap<3.6V
Bu ck outpu tU V/OV
Bu ckOC
LDO UV
CompensationpinshottoGND
Shutdown2
eFuse
ENUV/OV
VINOV
eFuseOC
VIN‐VOUT>560mV
ENUV
T
J
>155°C
&gotoShutdown2
whenT
J
>155°C
T
J
<135°C
&LDOnotUV
&StoragecapnotOV
&Bootcapnotfail
Shutdown1
Boost
Figure 3: State Machine Diagram
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States eFuse Boost Buck ADC V
REF
UV/POR
Disabled Disabled Disabled Disabled Disabled
SOFT-START
Enabled Disabled Disabled Disabled Enabled
NORMAL
Enabled Enabled Disabled Enabled Enabled
HEALT CHECK
Enabled Enabled Disabled Enabled Enabled
SUPPLEMENT
Disabled Disabled Enabled Enabled Enabled
SHUTDOWN1
Enabled Disabled Disabled Enabled Enabled
SHUTDOWN2
Disabled Disabled Disabled Disabled Disabled
Table 1: Enabled Functions in Different States
VIN
VOUT
VSTR
PLI
nIRQ
EN_UV
Buck_UV
Soft Start Boost On Supplement
Mode
10ms Delay
Boost
Enabled
(I2C)
Soft Start Boost On
10ms Delay
0
0
0
0
0
Figure 4: Operation states
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Pin Functions
VIN
VIN is the input the eFuse. Connect a 0.1uF ceramic
capacitor between VIN and PGND. VIN is directly
connected to VOUT in normal operation. The eFuse
disconnects VIN from VOUT when the IC enters
supplement mode.
EN
The EN pin is the ACT4910 enable input used to turn
the eFuse on or off. It provides both overvoltage and
undervoltage protection thresholds. The EN pin
contains a precision comparator with hysteresis. It can
be directly driven from a digital input to turn the eFuse
on and off. The EN pin can also be used with a resistor
divider from VIN to VSS to program an eFuse startup
voltage higher than the IC’s UVLO value. The EN pin
also contains an overvoltage comparator. The eFuse
turns on when the input EN pin goes above the
EN_UV_REF threshold. Once the eFuse is on, it turns
off and enters supplement mode if the EN pin goes
above the EN_OV_REF threshold or below the
EN_UV_REF threshold.
The EN pin should not be left floating. It can be driven
from standard logic signals greater than EN_UV_REF.
It can also be driven with open-drain logic to provide.
When driving it with an open-drain, ensure that the
pullup voltage is not higher than the EN_OV_REF
setting.
EN_UV_REF is fixed at 0.64V. However, the
EN_OV_REF can be programmed by I
2
C bits
EN_OV_REF [2:0]. The default EN_OV_REF voltage is
set by the IC’s CMI.
Table 2: Over Voltage Reference Settings
EN_OV_REF[2:0] OV Threshold (V)
000 Disabled
001 0.82
010 0.92
011 1.00
100 1.08
101 1.16
110 1.24
111 1.32
STR
STR is the output to the storage capacitor bank. In
normal operation the internal boost converter charges
the storage capacitors through the STR pin. When the
IC enters supplement mode, the internal buck converter
uses the STR pin as its input to power the system. The
STR pin typically has a 22uF or greater ceramic
capacitor. See the Buck Converter section for more
information.
IRQ—Interrupt
ACT4910 has an interrupt pin to inform the host of any
fault conditions. In general, any IC function with a status
bit asserts nIRQ if the status changes. The status
changes can be masked by setting the corresponding
register bits. If nIRQ is asserted low, the fault must be
read before the IC deasserts nIRQ. If the fault remains
after reading the status bits, nIRQ remains asserted.
The below status changes will set the IRQ:
Input overvoltage, undervoltage
Thermal warning, thermal shutdown
eFuse VIN to VOUT over limits
eFuse current warning and limit
Storage capacitor overvoltage, undervoltage
Supplemental mode active
Buck operation faults
Buck undervoltage shutdown
REF LDO undervoltage
ADC data is ready
ADC beyond set limits
nIRQ is an open-drain output and should be pulled up
to an appropriate supply voltage with a 10kΩ or greater
pull-up resistor.
SCL, SDA
SCL and SDA are the I
2
C clock and data pins to the IC
They have standard I
2
C functionality. They are open-
drain outputs and each require a pull-up resistor. The
pull-up resistor is typically tied to the system’s uP IO
pins. The pullup voltage can range from 1.8V to 5.0V.
REF
The REF pin is an internal bias voltage output pin.
Connect a 1µF capacitor between REF and VSS. Do
not apply an external load to the REF pin.
BSET
BSET sets the boost converter output voltage. The
output voltage is a function of both a resistor connected
between BSET and VSS as well as internal I
2
C register
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settings. See the Storage Boost Converter section for
more information.
ISET
ISET sets the eFuse current limit with a resistor
connected to VSS. See the eFuse section for more
information.
SS
The SS pin uses a capacitor to VSS to control the eFuse
softstart timing. See the eFuse section for more
information.
PGND
The PGND pin is the buck and boost converters’ power
ground. The internal FETs connect directly to the PGND
pins. The power supply input and output capacitors
should connect to the PGND pins.
COMP
COMP is the output of a transconductance amplifier that
is used to compensate the internal buck converter. The
compensation components, which are typically a
standard type-2 compensation should be grounded to
the VSS pin. See the Application section for more
information on compensating the internal buck
converter.
PLI
The PLI pin has four possible functions which are set by
the internal I
2
C registers.
Power Loss Indicator function. Set register bits
PLI_FUNC_SEL[1:0] in 0x19h to 00 to configure PLI for
this function. With this setting, PLI goes high when the
EN pin goes above EN_UV_REF and stays high in
normal operation. PLI immediately goes low when the
IC enters supplement mode. This setting is used to let
the system uP know that power loss is imminent.
PG_STR function. Set PLI_FUNC_SEL = 01 to
configure PLI for this function. With this setting, PLI
starts low during softstart and then goes high when the
storage capacitor voltage is in regulation. It goes low if
the storage voltage drops below 95% of its programmed
output voltage.
VOUT_READY function. Set PLI_FUNC_SEL = 10 to
configure PLI for this function. With this setting, PLI
starts low during softstart and then goes high when the
IC exits the softstart mode and goes into normal
operation. The IC exits softstart ~10ms after the
programmed softstart time ends.
PLI_VOUT_READY function. Set PLI_FUNC_SEL = 11
to configure PLI for this function. With this setting, PLI
performs a dual function. It starts out as the
VOUT_READY function at turn-on. After PLI goes from
low to high after softstart, it then acts as the Power Loss
Indicator function.
The PLI pin is an open-drain output and is 24V
compliant.
FB
The FB pin is used to regulate the buck converter output
voltage when the IC is in supplement mode.
HSB
HSB provides power to the internal high-side MOSFET
gate driver circuitry. Connect a 47nF capacitor from
HSB pin to SW pin.
SW
SW is the switch node for the internal buck and boost
converters.
VOUT
VOUT is the output of the eFuse and connects to the
system load. VOUT powers the boost converter when
it charges up the storage capacitors. It is the output of
the buck converter when the IC is in supplement
mode. The eFuse connects VOUT to VIN in normal
operation, and it disconnects it in supplement mode.
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EFUSE
General Description
The ACT4910 eFuse is an “electronic” fuse that
disconnects the input from the output. It has
considerable advantages over mechanical fuses
because it has adjustable current thresholds and it
resets after the fault condition is gone. The eFuse
consists of two back-to-back MOSFETS to provide bi-
directional protection. This provides protection against
both input and output short circuit conditions by
preventing current flow in both directions. Hot swap
functionality is provided by the eFuse softstart function
and current limiting circuitry. This prevents large inrush
currents from pulling down the input voltage. The eFuse
also provides protection against high input voltage
transients up to 24V by opening when the input voltage
goes above the programmed threshold.
The eFuse turns off in the following conditions.
1. EN voltage below UV threshold
2. EN voltage above the OV threshold
3. Input voltage above the OV threshold
4. eFuse current above the OC threshold
5. VIN – VOUT > 560mV
Current Limit Setting
A resistor connected between the ISET pin and VSS
program the ACT4910 eFuse inrush and maximum DC
current limits. The input current limit is linearly
proportional to the resistor value on the ISET pin. The
following equation calculates the correct resistor value
to get the desired current limit threshold.



Equation (1)
Where R
ILIM
is the current limit resistor in ohms and I
ILIM
is the desired current limit threshold in Amperes. Figure
5 shows the current limit setting vs R
ILIM
value.
Figure 5: Current Limit Threshold vs
R
ILIM
Note that the eFuse current can be measured using the
ILIM pin. If eFuse current is measured via the ILIM pin,
the measurement circuit must have a high impedance
input to minimize errors. The current flowing out of ILIM
is 1/50000 of the current through the eFuse. The
following equation calculates the eFuse current when
measured via the ILIM pin.

∗

Equation (2)
Where R
ILIM
is the current limit resistor in ohms and V
ILIM
is the voltage on the ILIM pin in volts.
When the eFuse reaches the current limit threshold, it
clamps the output current. If the load tries to draw
additional current, the eFuse opens.
Soft-Start
The SS pin controls the eFuse start-up. The SS pin
drives a constant 5μA internal current source into the
external soft-start capacitor to provide a linear ramping
voltage at the SS pin. The output voltage linearly ramps
with the SS pin voltage, resulting in a well-controlled
linear softstart ramp on VOUT, regardless of the load
conditions. The following equation calculates the
required soft-start capacitance.
𝐶󰇛𝑛𝐹󰇜

󰇛󰇜

󰇛󰇜 Equation 2
Where the T
SS
is the soft-start time in ms and V
OUT
is the
output voltage.
The softstart current must be less than 90% of the
programmed eFuse current limit. If the softstart current
is greater than 90% of the eFuse current limit, the IC
enters the SHUTDOWN2 state, turns off the eFuse, and
0.000
2.000
4.000
6.000
8.000
10.000
12.000
14.000
0 102030405060
OutputCurrent(A)
RISET(kΩ)
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then retries to softstart again. The following equation
calculates the minimum allowable softstart time.
𝑇_󰇛𝑚𝑠󰇜

󰇛󰇜∗ 

.∗

󰇛󰇜 Equation 3
Where C
OUT
is the sum of the output capacitance and
storage capacitance in mF, V
OUT
is the output voltage in
volts, and I
ILIM
is the eFuse current limit in Amperes
programmed by the ILIM resistor.
Buck Converter
General Description
The ACT4910 contains current-mode, synchronous
PWM step-down converter that achieves peak
efficiencies of 95%. The buck converter minimizes noise
in sensitive applications and allows the use of small
external components. It is highly flexible with external
component selection and can be reconfigured via I
2
C
registers. External components set the output voltage
and compensation while I
2
C registers set the switching
frequency and current limit. The buck converter
operates in fixed frequency PWM mode. Its switching
frequency is programmable between 320kHz to 1130
kHz via the I
2
C register BK_FREQ[2:0] which allows the
system to be optimized for different applications. Its
current limit is adjustable between 5A to 9A, allowing for
further system optimization. The output voltage is
externally programmable between 1.8V and 18V.
The buck converter generates a regulated output
voltage at the VOUT pin from the storage capacitors
when the IC enters supplement mode. This provides the
backup power when the system experiences fault
conditions. After the IC exits the SOFTSTART state, the
buck converter is enabled but remains turned off. It
automatically turns on when the IC enters supplement
mode, and remains on until the storage capacitors
discharge to 3.6V.
Frequency Setting
Higher switching frequencies result in smaller solution
sizes at the cost of slightly lower efficiency. Lower
switching frequencies result in larger solution sizes
with higher efficiency. The maximum allowable
switching frequency for any given design is limited by
the following equation.
𝐹
_


∗
Equation 3
Where F
SW_max
is the maximum allowable frequency,
V
STR
is the storage voltage, and V
OUT
is the output
voltage during supplement mode.
Output Voltage Setting
The buck converter output voltage is programmed by an
external resistor divider connected between the VOUT
pin and VSS, with the center tap connected to the FB
pin. The buck output voltage can be set above, below,
or equal to the input voltage supplement threshold.
When the input voltage drops below this threshold, the
IC enters supplement mode and regulates the output to
the programmed buck voltage. Although the buck
converter immediately starts up when the IC enters
supplement mode, the output voltage still has a small,
but finite drop in output voltage between the time the
eFuse turns off and the buck converter is fully on. This
voltage drop should be considered when setting the
output voltage. The following equation calculates the
correct resistor values to set the desired output voltage.
𝑅1 R2 ∗ 󰇡


1󰇢 Equation 4
Where R1 is the top feedback resistor, R2 is the bottom
feedback resistor, VOUT is the desired output voltage,
and VFB is the fixed 1.2V reference voltage on the FB
pin. Choose R2 in the range of 10kohm. Smaller
resistor values are acceptable, but larger values will
affect voltage accuracy due to bias currents into the FB
pin.
Protection
The buck converter has several protection mechanisms
to insure safe operation. It stops operation when input
voltage from storage cap reaches STR_UVLO (3.6V) or
when the output voltage drops below the power good
threshold which is fixed at 93% of the output setpoint. It
also stops operating when the output voltage is above
the over voltage threshold which is fixed at 110% of the
output voltage setpoint. The output undervoltage
protection can be masked by the I
2
C register bit
Mask_BK_UV REG0x38 [0].
The buck converter provides overcurrent and short
circuit protection. Overcurrent protection is achieved
with cycle-by-cycle current limiting. The peak current
threshold is set between 5A and 9A by the BK_CLIM bits.
If the peak current reaches the programmed threshold,
the IC turns off the power FET. This condition typically
results in shutdown due to an output voltage UV
condition due to the shortened switching cycle.
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Table 3: Buck Current Limit
BK_CLIM[1:0] ILIMSET (A)
00 5.0
01 6.0
10 7.0
11 9.0
A short circuit condition that results in the peak switch
current being 122.5% of BK_CLIM immediately shuts
down the supply and asserts nIRQ low. A buck
overcurrent, undervoltage, or overvoltage condition
moves the IC into the UV/POR state.
Compensation
The Buck regulator utilizes type 2 external
compensation placed on the COMP pin. Contact the
factory for compensation details.
Input Capacitor Selection
The STR pin is the input voltage to the buck converter.
It requires a dedicated high quality, low-ESR, ceramic
input capacitor that is optimally placed to minimize the
power routing. For optimal PCB layout considerations,
1206 or 1210 sized input capacitors are recommended.
A 22uF capacitor is typically suitable, but the actual
value is application dependent. The input capacitor can
be increased without limit. Choose the input capacitor
value to keep the input voltage ripple less than 50mV
𝐶
 𝐼𝑜𝑢𝑡∗


∗



∗

Equation 5
Where Iout is the maximum eFuse load current in
Amperes, V
STR
is the maximum storage voltage, F
SW
is
the switching frequency, and V
ripple
is the maximum
allowable ripple voltage on the input of the buck
converter. Note that the storage capacitor values should
not be considered when calculating the input voltage
ripple because they are not typically designed for high
frequency functionality.
Be sure to consider the input capacitor’s DC bias effects.
A capacitor’s actual capacitance is strongly affected by
its DC bias characteristics. The input capacitor is
typically an X5R, X7R, or similar dielectric. Use of Y5U,
Z5U, or similar dielectrics is not recommended. Input
capacitor placement is critical for proper operation. The
buck’s input capacitor must be placed as close to the IC
as possible. The traces from STR to the capacitor and
from the capacitor to PGND should as short and wide
as possible.
Inductor Selection
The Buck regulator utilizes current-mode control and a
proprietary internal compensation scheme to
simultaneously simplify external component selection
and optimize transient performance over their full
operating range. These ACT4910 is optimized for
operation with 1uH to 3.3uH inductors. Choose an
inductor with a low DC-resistance, and avoid inductor
saturation by choosing inductors with DC ratings that
exceed the maximum output current by at least 30%.
Due to the requirement for the buck converter to start
up as quickly as possible, the inductor should be
designed to give a maximum ripple current, ΔI
L
, of 50%
to 60% of the maximum output current. The following
equation calculates the recommended inductor value.
𝐿 


∗ 


∗∆
Equation 6
Where L is the inductor value in µH, V
OUT
is the output
voltage, V
STR
is the maximum storage voltage, F
SW
is
the switching frequency in Hz, and ΔI
L
is the desired
ripple current in Amperes.
Output Capacitor Selection
The buck converter is designed to take advantage of the
benefits of ceramic capacitors, namely small size and
very-low ESR. The buck converter is designed to
operate with 44µF output capacitor over most of its
operating ranges, although more capacitance may be
desired depending on the duty cycle and load step
requirements. Choose a ripple voltage that is
approximately 1% of the output voltage setpoint. Note
that the output capacitance must be placed at the output
of the buck converter. Additional downstream
capacitance will be placed at the loads, but this
capacitance should not be considered when calculating
the buck output capacitance. However, the downstream
capacitance should be considered when compensating
the power supply. The following equation calculates the
output voltage ripple as a function of output capacitance.
Note that the worst case ripple voltage occurs at the
beginning of supplement mode when the storage
capacitors are fully charged.
C
OUT
∆
∗

∗

Equation 7
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Where V
ripple
is the desired output ripple voltage, F
SW
is
the switching frequency in Hz, and ΔI
L
is the maximum
ripple current in Amperes.
As with the input capacitor selection, use X5R or X7R
dielectrics and be sure to consider the capacitor’s DC
bias effects.
Storage Boost Converter
General Description
The ACT4910 contains an integrated peak current-
mode, synchronous boost converter. It minimizes
system level costs by using the same components as
the buck converter. The peak current is adjustable
between 250mA and 950mA, allowing for system
optimization. The output voltage is adjustable between
5V and 36V via I
2
C registers and an external resistor.
The peak current-mode control topology eliminates the
need for compensation. The boost automatically
charges up the storage capacitors from the input
voltage so they are ready to provide backup power in
the event of a system fault.
Startup
The boost converter automatically starts when the IC
exits the SOFTSTART state. Note that the IC exits the
SOFTSTART state 10ms after the output voltage is
within 200mV of the input voltage. Note that the storage
capacitor voltage is initially checked 100ms after the
boost is enabled. If the storage voltage does not reach
its regulation limit by this time, the I2C STR_UV bit is
set. If the storage capacitors are charging too slowly,
use a larger boost current limit value (set by I2C bits
BST_CLIM in register 0x21h) or smaller storage
capacitance.
When the storage voltage reaches regulation, the boost
enters standby mode and monitors the storage voltage.
It automatically turns back on and “tops off” the storage
capacitors when the storage voltage drops below 95%
of the programmed voltage. The boost converter
automatically turns off if it is “topping off” the storage
capacitors when the IC enters supplement mode.
The average input current when the boost charges the
storage capacitors is approximately ½ of the peak
switching current. The peak switch current is programed
by register BST_CLIM[1:0].
Table 4: Boost Peak Current Settings
BST_CLIM[1:0] (mA)
00 250
01 650
10 950
11 1500
Operating Mode
The boost converter operates in peak current mode,
non-fixed frequency mode. The power FET stays on
until its current reaches programmed peak current. It
then turns off until the inductor current drops to 0A, at
which time it turns on again.
Storage Capacitor Voltage Setting
The buck converter output voltage is set by either the
I
2
C register BSTVSET[4:0], or a combination the
register and a resistor placed between the BSET pin to
VSS.
When using only the BSTVSET[4:0] leave the BSET pin
floating. Table 5 shows the programmed storage voltage.
The default value is determined by the IC’s specific CMI
option.
Table5: Storage Capacitor Voltage Settings with
BSET Pin Open
BSTVSET[3:0] BSTVSET[4]
0 1
0000 5V 21V
0001 5.6V 22V
0010 7V 23V
0011 8V 24V
0100 9V 25V
0101 10V 26V
0110 11V 27V
0111 12V 28V
1000 13V 29V
1001 14V 30V
1010 15V 31V
1011 16V 32V
1100 17V 33V
1101 18V 34V
1110 19V 35V
1111 20V 36V
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Using both the BSTVSET[4:0] register and an external
resistor provides additional output voltage resolution. In
this configuration, the following equation calculates the
output voltage.
𝑉 𝑉
 ∗

Ω Equation 8
Where V
BSTVSET
is the voltage set by the BSTVSET
register in Table 5 and R
BSET
is the resistor on the BSET
pin in ohms.
As an example, with BSTVSET[4:0] = 10111 (sets
V
BSTVSET
= 28V) and R
BSET
= 34.2kΩ, V
STR
= 12.8V. Note
that R
BSET
should be set between 20kΩ and 75kΩ.
Setting R
BSET
below 20kΩ gives the same result as
using a 20kΩ resistor. Setting R
BSET
above 75kΩ gives
the same result as using a 75kΩ resistor. Using R
BSET
outside the range is acceptable and does not damage
the IC.
Input Capacitor Selection
There are no special considerations for the boost
converter input capacitor. The IC topology uses the
buck converter output capacitor for the boost input
capacitor. Proper selection of the buck converter output
capacitor automatically results in an acceptable boost
converter input capacitor.
Output Inductor Selection
There are no special considerations for the boost
converter inductor. The IC topology uses the buck
converter inductor for the boost converter inductor.
Proper selection of the buck converter output capacitor
automatically results in an acceptable boost converter
input capacitor.
Output Capacitor Selection
The IC topology uses the buck converter input capacitor
for the boost converter output capacitor. Note that the
storage capacitors are also included in the boost
converter output capacitors. Proper selection of the
buck converter input capacitor typically results in an
acceptable boost converter output capacitor. The boost
output capacitor has two criteria. The first is that it must
consist of at least 10µF of high quality X5R or X7R
ceramic capacitance placed directly between the STR
pin and PGND. The second criteria is that the sum of
the ceramic capacitor and storage capacitors must be
greater than 100µF. There is no requirement for the
additional capacitance dielectric material. This provides
flexibility for the storage capacitors, which allows the
use of super capacitors, electrolytic, polymer, Tantalum,
ceramic, or any capacitors in the design.
Output Voltage UVLO Setting
The storage capacitor power good signal indicates that
the STR voltage is above the UVLO threshold. The
UVLO threshold is shared with the storage capacitor
health check, and is set by the I
2
C register HMON_THR
[3:0]. The default value is determined by the IC’s
specific CMI option.
Table 6: Storage Capacitor PG Threshold
HMON_THR[2:0] HMON_THR[3]
0 1
000 95.0% 96.6%
001 95.2% 96.8%
010 95.4% 97.0%
011 95.6% 97.2%
100 95.8% 97.4%
101 96.0% 97.6%
110 96.2% 97.8%
111 96.4% 98.0%
Storage Capacitor Health Monitor
General Description
The ACT4910 has an internal health monitor for the
storage capacitors. It applies a constant current sink to
the capacitors and monitors the voltage drop. If the
voltage drops below a predetermined threshold, the IC
asserts nIRQ to indicate that the storage capacitance
has dropped below the allowable threshold. Health
monitoring is completely autonomous, but can also be
manually initiated by the system uP. Health monitoring
can also be configured so that it is only a manual
operation so it can be triggered on demand to avoid any
critical system operations. The health monitor
parameters are adjustable via I
2
C registers to allow
flexibility for different capacitor values.
Health Monitor Algorithm
The health check algorithm sinks 10mA into the STR pin
for a time determined by I
2
C register HMON_TSET. It
then sinks 50mA for 200us. It monitors the voltage on
the STR pin, and if the voltage drops more than the
percentage set by I
2
C register HMON_THR, it asserts
nIRQ low and sets the fault bit. The IC’s specific CMI
option sets the default HMON_TSET and HMON_THR
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settings. After the HMON_TSET time, the boost turns
back on to recharge the storage capacitor.
The health check function can be enabled and disabled
by the DIS_HEALTH_CHK bit (0x1Fh [5]). It also can be
forced to perform a one-shot health check by the
FORCE_HLTHCHK bit (0x0Ah [1]). Forcing a single
health check is valid even when the DIS_HEALTH_CHK
bit =1. If set in continuous mode, the IC performs a
health check every 4 minutes. This timing can be
configured for every 8 minutes or 16 minutes by bits
SCALE_HCHK _2X and SCALE_HCHK _4X in register
0x27h [1:0].
The ACT4910 allows for very flexible health checking
routines by allowing the system to manually enable the
10mA discharge current by setting the
EN_STR10mASINK bit = 1. In this situation, the system
manually turns the discharge current on and off. The
storage capacitor voltage threshold is still determined
by the HMON_THR register. This function is useful for
checking extremely large capacitor values which need
very long discharge times.
PG_THR
(Programmable)
V
STR
Initial Charge Health Testing Top-Off
Maintain
V
10mA
50mA
I
200us
Pr og ra mm ab le
Discharge Time
Pr og ra mm ab le
Interval Time
t
t
0
0
St ora ge C a p V ol tag e
Discharge Current
Figure 6: Storage Voltage at Different Stages
The register HMON_TSET [3:0] sets the health check
discharge time as shown in Table 7. This also allows the
use of the ADC to check the slope of the discharge and
calculate the capacitance.
Table 7: Health Check Discharge Time
HMON_TSET[2:0] HMON_TSET[3] (ms)
0 1
000 2 384
001 4 512
010 8 640
011 16 768
100 32 896
101 64 1024
110 128 1152
111 256 1280
ADC Monitoring
General Description
The ACT4910 contains a built-in analog to digital con-
verter, ADC, which can be used to monitor five system
level parameters. These include input voltage, output
voltage, storage capacitor voltage, eFuse current, and
die temperature. It is a single 8 bit delta-sigma ADC that
uses an analog input multiplexer to select one of six
channels for the A/D conversion. The resulting digital
results are stored in six digital registers. A six to one
multiplexer connects one of the ADC output registers to
the user accessible register map.
ADC Configuration
The ACT4910 ADC is configured through the I
2
C
interface. It is enabled and disabled by the EN_ADC
register bit. The ADC has two conversion modes,
manual single-shot conversion and automatic polling
conversion.
Single-Shot Conversion
Configure the IC for single-shot conversion mode by
setting the following I
2
C bits in register 0x08h
ADC_ONE_SHOT = 1.
ADC_CH_SCAN = 0
EN_ADCBUF = 1
In single shot mode, the user defines the input channel
to be converted and then manually initiates the ADC
conversion. I
2
C bits ADC_CH_CONV [2:0] in register
0x08h select the input channel to be converted.
ADC_CH_READ [2:0] selects the ADC channel to be
read. These should be set to the same channel. The
user initiates an ADC read by writing a 1 into EN_ADC
in register 0x08h. When ADC conversion is complete,
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the ADC_DATA_READY bit (register 0x07h [7]) is set to
1, nIRQ is asserted low, and EN_ADC automatically
changes back to 0. The uP can then read the status bits
to find that the ADC conversion is complete. The ADC
data are stored in ADC_DOUT [13:6] in register 0x05h.
nIRQ stays asserted low and the ADC_READY_BIT
stays equal to 1 until the ADC data is read. Reading the
ADC data automatically deasserts nIRQ. To initiate
another ADC conversion for the same channel, set
EN_ADC=1. To initiate an ADC conversion for another
channel, change ADC_CH_CONV and
ADC_CH_READ to the appropriate channel and then
set EN_ADC=1.
6 to 1
MUX ADC
CH0
CH1
CH5
CH2
8 Bit
Result
Clock
SEL[2:0]
Figure 7: ADC Block Diagram
Automatic Polling Conversion
Configure the IC for automatic polling conversion mode
by setting the following I
2
C bits in register 0x08h
ADC_ONE_SHOT = 0
ADC_CH_SCAN = 1
EN_ADCBUF = 1
Start the automatic polling by changing EN_ADC to 1.
When in automatic polling mode, the ADC continuously
changes the MUX inputs to read all input channels. The
ADC continually overwrites the data in the output
register. After all channels have been converted, the
ADC_DATA_READY bit is set to 1. Note that nIRQ is not
asserted low in Automatic Polling mode. Ensure that
ADC data is valid and ready by reading the
ADC_DATA_READY before reading ADC data. After the
ADC_DATA_READY bit is set to 1, the user defines the
channel to be read with the ADC_CH_CONV [2:0] bits
in register 0x08h. Change ADC_CH_CONV to read
additional channels.
Table 8: ADC Channels
Channel Channel Description ADC_CH_CONV[2:0] ADC_CH_READ[2:0] Value
CH0 Input Current 000 000 IIN = (DOUT-128)*1.221/RILIM (A)
CH1 Input Voltage 001 001 VIN = (DOUT-128)*0.392 (V)
CH2 Storage Cap Voltage 010 010 VSTR = (DOUT-128)*0.392 (V)
CH3 Output Voltage 011 011 VOUT = (DOUT-128)*0.392 (V)
CH4 Die Temperature 100 100 Temp = 6.125*DOUT-1053.75 (deg C)
CH5 GND 101 101
Autonomous ADC Supervisory Function
The ACT4910 can be configured to automatically
measure any or all of the five system level parameters
and then then automatically notify the system if one of
the parameters falls out of its specified range. This
check is performed automatically, without any external
circuit components. The ACT4910 implements this
using internal digital undervoltage and overvoltage
comparators for all five ADC channels. Table 9 shows
each ADC channel’s undervoltage and overvoltage
registers. When in automatic polling mode, if an ADC
conversion result is below the undervoltage threshold or
above the overvoltage threshold, the IC asserts nIRQ
low. The uP can then read the status register 0x04h to
determine which parameter is out of range. nIRQ can
be masked by setting the ADC_OUTRNG_IRQ_MASK
bit. The default thresholds are determined by each ICs
CMI, but can be changed at any time after startup.
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Disable a channel’s supervisory function by
programming the undervoltage register value to 0x00h
and the overvoltage register to 0xFFh.
Table 9: ADC Thresholds Registers
Undervoltage
Threshold Register
Overvoltage
Threshold Register
Input Current 0x0Ch 0x14h
Input Voltage 0x0Dh 0x15h
Storage Cap Voltage 0x0Eh 0x16h
Output Voltage 0x0Fh 0x17h
Die Temperature 0x10h 0x18h
PC board layout guidance
Proper parts placement and PCB layout are critical to
the operation of switching power supplies. Follow the
following layout guidelines when designing the
ACT4910 PCB. Refer to the Active-Semi ACT4910
Evaluation Kits for layout examples
1. Place the buck input capacitors as close as
possible to the IC. Connect the input capacitors
directly between STR and PGND pins on the
top layer. Routing these traces on the top layer
eliminates the need for vias.
2. Minimize the switch node trace length between
the SW pin and the inductor. Optimal switch
node routing is to run the trace between the in-
put capacitor’s pads. Using 1206 or larger sized
input capacitors is recommended. Avoid routing
sensitive analog signals near these high fre-
quency, high dV/dt traces.
3. The Buck output capacitors should be placed
by the inductor and connected directly to the in-
ductor and ground plane with short and wide
traces. The output capacitor ground should
make a short connection to the input capacitor
ground. If required, use multiple vias.
4. The FB pin should be Kelvin connected to the
output capacitor through the shortest possible
route, while keeping sufficient distance from
switching node to prevent noise injection. The
IC regulates the output voltage to this Kelvin
connection.
5. Connect the PGND and VSS ground pins must
be electrically connected together. The VSS
ground plane should be isolated from the rest
of the PCB power ground.
6. Remember that all open drain outputs need
pull-up resistors.
7. Connect the exposed pad directly to the top
layer ground plane. Connect the top layer
ground plane to both internal ground planes
and the PCB backside ground plane with ther-
mal vias. Provide ground plane routing on mul-
tiple layers to allow the IC’s heat to flow into the
PCB and then spread radially from the IC. Avoid
cutting the ground planes or adding vias that re-
strict the radial flow of heat.
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Typical Operating Characteristics
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ACT4910QW
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ACT4910QW
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ACT4910QW
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CMI OPTIONS
This section provides the basic default configuration settings for each available ACT4910 CMI option. Refer to each
option’s application note for the comprehensive list of default settings
CMI 121: ACT4910QW121
CMI 121 is designed for standard 12V applications. CMI 121 default settings are appropriate for most typical applications.
It provides the fastest buck switching frequency for the smallest solution sizes. Table 10 shows the default register
settings.
Table 10: CMI 121 Default Register Settings
Function Value Register Register Settings
PLI Pin Function PLI & VOUT OK 0x19h PLI_FUNC_SEL[1:0] = 11
Health Monitor Time 32ms 0x1Fh HMON_TSET[3:0] = 0100
Health Monitor Threshold 96% 0x20h HMON_THR[3:0] = 0101
Enable Overvoltage Reference 0.92V 0x20h EN_OV_REF[2:0] = 010
Startup Delay 0ms 0x20h EN_STARTDELAY = 0
Latch Supplement Mode Yes 0x21h EN_LATCH_SPLMNT = 1
Boost Current Limit 950mA 0x21h BST_CLIM[1:0] = 10
Boost Voltage 28V 0x21h BST_VSET[4:0] = 10111
Buck Peak Current Limit 9A 0x26h BK_CLIM[1:0] = 11
Buck Switching Frequency 1130kHz 0x28h BK_FREQ[2:0] = 111
I2C Address
The CMI 121 7-bit I2C address is 0x5Ah. This results in 0xB4h for a write address and 0xB5h for a read address.
Device ID
The CMI 121 Device ID (register 0x3Bh) = 0x02h. This can be used to distinguish between different CMI versions.
Autonomous ADC Supervisory Function
The autonomous ADC supervisory function is disabled by default. All undervoltage register value are set to 0x00h and
all overvoltage register values are set to 0xFFh.
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CMI 122: ACT4910QW122
CMI 122 is designed for standard 12V applications. CMI 122 default settings are appropriate for most typical applications.
It provides the 900kHz buck switching frequency to compromise size and efficiency. The default storage voltage is 36V
which allows for maximum capacitor energy storage. Placing a resistor between BSET and VSS can program the default
storage voltage to a lower value. Table 11 shows the default register settings.
Table 11: CMI 122 Default Register Settings
Function Value Register Register Settings
PLI Pin Function PLI & VOUT OK 0x19h PLI_FUNC_SEL[1:0] = 11
Health Monitor Time 32ms 0x1Fh HMON_TSET[3:0] = 0100
Health Monitor Threshold 97.2% 0x20h HMON_THR[3:0] = 1011
Enable Overvoltage Reference 0.92V 0x20h EN_OV_REF[2:0] = 010
Startup Delay 0ms 0x20h EN_STARTDELAY = 0
Latch Supplement Mode Yes 0x21h EN_LATCH_SPLMNT = 1
Boost Current Limit 950mA 0x21h BST_CLIM[1:0] = 10
Boost Voltage 36V 0x21h BST_VSET[4:0] = 11111
Buck Peak Current Limit 9A 0x26h BK_CLIM[1:0] = 11
Buck Switching Frequency 900kHz 0x28h BK_FREQ[2:0] = 110
I2C Address
The CMI 122 7-bit I2C address is 0x5Ah. This results in 0xB4h for a write address and 0xB5h for a read address.
Device ID
The CMI 122 Device ID (register 0x3Bh) = 0x03h. This can be used to distinguish between different CMI versions.
Autonomous ADC Supervisory Function
The autonomous ADC supervisory function is disabled by default. All undervoltage register value are set to 0x00h and
all overvoltage register values are set to 0xFFh.
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CMI 123: ACT4910QW123
CMI 123 is designed for standard 12V applications. CMI 123 default settings are appropriate for most typical applications.
It uses a 250mA boost current limit setting to minimize input currents during system level turn on. It provides the 900kHz
buck switching frequency to compromise size and efficiency. The default storage voltage is 27V for compatibility with
80% derated 35V capacitors. Placing a resistor between BSET and VSS can program the default storage voltage to a
lower value. Table 12 shows the default register settings.
Table 12: CMI 123 Default Register Settings
Function Value Register Register Settings
PLI Pin Function PLI & VOUT OK 0x19h PLI_FUNC_SEL[1:0] = 11
Health Monitor Time 32ms 0x1Fh HMON_TSET[3:0] = 0100
Health Monitor Threshold 95% 0x20h HMON_THR[3:0] = 0000
Enable Overvoltage Reference 0.92V 0x20h EN_OV_REF[2:0] = 010
Startup Delay 0ms 0x20h EN_STARTDELAY = 0
Latch Supplement Mode Yes 0x21h EN_LATCH_SPLMNT = 1
Boost Current Limit 250mA 0x21h BST_CLIM[1:0] = 00
Boost Voltage 27V 0x21h BST_VSET[4:0] = 10110
Buck Peak Current Limit 5A 0x26h BK_CLIM[1:0] = 00
Buck Switching Frequency 900kHz 0x28h BK_FREQ[2:0] = 110
I2C Address
The CMI 123 7-bit I2C address is 0x5Ah. This results in 0xB4h for a write address and 0xB5h for a read address.
Device ID
The CMI 123 Device ID (register 0x3Bh) = 0x04h. This can be used to distinguish between different CMI versions.
Autonomous ADC Supervisory Function
The autonomous ADC supervisory function is disabled by default. All undervoltage register value are set to 0x00h and
all overvoltage register values are set to 0xFFh.
Health Check
The health check function is disabled by default.
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CMI 302: ACT4910QW302
CMI 302 is designed for standard 3.3V applications. CMI 302 default settings are appropriate for most typical
applications. It uses a 650mA boost current limit setting to limit inrush current and still quickly charge up the storage
caps. It provides a 560kHz buck switching frequency. The default storage voltage is 27V for compatibility with 80%
derated 35V capacitors. Placing a resistor between BSET and VSS can program the default storage voltage to a lower
value. Table 13 shows the default register settings.
Table 13: CMI 302 Default Register Settings
Function Value Register Register Settings
PLI Pin Function PLI & VOUT OK 0x19h PLI_FUNC_SEL[1:0] = 11
Health Monitor Time 32ms 0x1Fh HMON_TSET[3:0] = 0100
Health Monitor Threshold 95% 0x20h HMON_THR[3:0] = 0000
Enable Overvoltage Reference 0.82V 0x20h EN_OV_REF[2:0] = 001
Startup Delay 0ms 0x20h EN_STARTDELAY = 0
Latch Supplement Mode Yes 0x21h EN_LATCH_SPLMNT = 1
Boost Current Limit 650mA 0x21h BST_CLIM[1:0] = 01
Boost Voltage 27V 0x21h BST_VSET[4:0] = 10110
Buck Peak Current Limit 5A 0x26h BK_CLIM[1:0] = 00
Buck Switching Frequency 560kHz 0x28h BK_FREQ[2:0] = 100
I2C Address
The CMI 302 7-bit I2C address is 0x5Ah. This results in 0xB4h for a write address and 0xB5h for a read address.
Device ID
The CMI 302 Device ID (register 0x3Bh) = 0x05h. This can be used to distinguish between different CMI versions.
Autonomous ADC Supervisory Function
The autonomous ADC supervisory function is disabled by default. All undervoltage register values are set to 0x00h and
all overvoltage register values are set to 0xFF
Health Check
The health check function is disabled by default.
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PACKAGE OUTLINE AND DIMENSIONS QFN5X5-28
Top View
Side View
Bottom View
ACT88320 LAND PATTERN
See Active Semi Application note AN-104, QFN PCB Layout Guidelines for more information on generating the
ACT4910 land pattern.