MIC68400
4A Sequencing LDO with Tracking and
Ramp Control™
Ramp Control is a trademark of Micrel, Inc.
MLF and MicroLeadFrame is a registered trademark of Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
June 2007 M9999-061907-B
General Description
The MIC68400 is a high peak current LDO regulator
designed specifically for powering applications such as
FPGA core voltages that require high start up current with
lower nominal operating current. Capable of sourcing 4A of
current for start-up, the MIC68400 provides high power
from a small MLF
®
leadless package. The MIC68400 can
also implement a variety of power-up and power-down
protocols such as sequencing, tracking, and ratiometric
tracking.
The MIC68400 operates from a wide input range of 1.65V
to 5.5V, which includes all of the main supply voltages
commonly available today. It is designed to drive digital
circuits requiring low voltage at high currents (i.e. PLDs,
DSP, microcontroller, etc.). The MIC68400 incorporates a
delay pin (Delay) for control of power on reset output
(POR) at turn-on and power-down delay at turn-off. In
addition there is a ramp control pin (RC) for either tracking
applications or output voltage slew rate adjustment at turn-
on and turn-off. This is important in applications where the
load is highly capacitive and in-rush currents can cause
supply voltages to fail and microprocessors or other
complex logic chips to hang up.
Multiple MIC68400s can be daisy chained in two modes.
In tracking mode the output voltage of the Master drives
the RC pin of a Slave so that the Slave tracks the main
regulator during turn-on and turn-off. In sequencing mode
the POR of the Master drives the enable (EN) of the Slave
so that it turns on after the Master and turns off before (or
after) the Master. This behavior is critical for power-up and
power-down control in multi-output power supplies. The
MIC68400 is fully protected offering both thermal, current
limit protection, and reverse current protection.
The MIC68400 has a junction temperature range of
–40°C to +125°C and is available in fixed as well as an
adjustable option. The MIC68400 is offered in the tiny
16-pin 4mm x 4mm MLF
®
package.
Features
• Stable with 10µF ceramic capacitor
• Input voltage range: 1.65V to 5.5V
• 0.5V reference
• ±2.0% output tolerance over tempe ratu re
• 4A maximum output current – peak start up
• 3A continuous operating current
• Tracking on turn-on and turn-off with pin strapping
• Timing controlled sequencing on/off
• Programmable Ram p Control™ for in-rush current
limiting and slew rate control of the output voltage
during turn-on and turn-off
• Power-on reset (POR) supervisor with prog rammable
delay time
• Single master can control multiple slave regulators
with tracking output voltages
• Tiny 4mm x 4mm MLF
®
package
• Maximum dropout (V
IN
– V
OUT
) of 500mV over
temperature at 3A output current
• Fixed and adjustable output voltages
• Excellent line and load regulation specifications
• Logic controlled shutdown
• Thermal shutdown and current limit protection
Applications
• FPGA/PLD power supply
• Networking/telecom equipment
• Microprocessor core voltage
• High efficiency linear post regulator
• Sequenced or tracked power supply
Micrel, Inc. MIC68400
June 2007 2 M9999-061907-B
Typical Application
Sequenced Dual Power Supply for I/O and Core Voltage of µProcess or
Micrel, Inc. MIC68400
June 2007 3 M9999-061907-B
Tracking Dual Power Supply for I/O and Core Voltage of µProcessor
Micrel, Inc. MIC68400
June 2007 4 M9999-061907-B
Block Diagram
Bandgap
Reference
Output Error
Holdoff
Thermal
Shutdown
Low Voltage
Holdoff
Sequencing
Timer/Controller
BGStart
BGDis
Ramp
Control
RCDis
IN
RC
EN
DLY BGStart: BandGap Startup
BGDis: BandGap Shutdown
RCDis: Ramp Control Discharge GND
POR
SNS
OUT
RC
Buffer
Error
Amp
Current
Driver
Current
Limit
External on
Adjustable Part
AMP
MIN
Ordering Information
Part Number Output
Current
Voltage Junction
Temperature Range
Package
MIC68400-1.8YML 4.0A 1.8V –40°C to +125°C PB-Free 16-Pin 4x4 MLF
®
MIC68400YML 4.0A ADJ –40°C to +125°C PB-Free 16-Pin 4x4 MLF
®
NOTE: For additional voltage options, contact Micrel Marketing.
Micrel, Inc. MIC68400
June 2007 5 M9999-061907-B
Pin Configur ation
16-Pin 4mm × 4mm MLF
®
(ML)
Fixed Voltages 16-Pin 4mm × 4mm MLF
®
(ML)
Adjustable Voltages
Pin Description
(Pin Numbering may change depending on layout considerations)
Pin Number
MIC68400YML Pin Name Pin Function
1, 2, 15, 16 VIN Input: Input voltage supply pin. Place a capacitor to ground to bypass the
input supply.
3 Delay
Delay: Capacitor to ground sets internal delay timer. Timer delays power-on
reset (POR) output at turn-on, and ramp down at turn-off.
4 RC
Ramp Control: May be voltage driven for tracking applicati ons or a capacitor
to ground will set the slew rate of output voltage during start-up.
5 EN
Enable (Input): CMOS compatible inp ut. Logic hig h = enable, logic low =
shutdown.
6, 14 NC Not internally connected.
7, 8, Tab GND Ground.
9 POR
Power-on Reset: Open-drain output device i ndicates when the output is in
regulation. High (open) means device is regulating within 10%. POR onset
can be delayed using a si ngle capacitor from Delay to ground.
10 (Fixed) SNS Output Voltage Sense Pin: Connect directly to output pin.
10 (ADJ) ADJ Adjustable regulators: Feedback input. Connect to resistor voltage d ivid er.
11, 12, 13 VOUT Output Voltage: Output of voltage regulator. Place capacitor to ground to
bypass the output voltage. Minimum load current is 100µA. Nominal bypass
capacitor is 10µF.
Micrel, Inc. MIC68400
June 2007 6 M9999-061907-B
Absolute Maximum Ratings(1)
Supply Voltage (V
IN
).........................................................6V
Enable Input Voltage (V
EN
)...............................................6V
POR (V
POR
)...........................................................V
IN
+ 0.3V
RC .......................................................................V
IN
+ 0.3V
Power Dissipation ..................................Internally Limited
(3)
Junction Temperature.........................–40°C ≤ T
J
≤ +125°C
Storage Temperature (T
S
)...................–65°C ≤ T
J
≤ +150°C
ESD Rating
(4)
.................................................................2kV
Operating Ratings(2)
Supply voltage (V
IN
) ....................................... 1.65V to 5.5V
Enable Input Voltage (V
EN
).....................................0V to V
IN
Ramp Contro l (V
RC
)............................................. 0V to 5.5V
Junction Temperature Range ............–40°C ≤ T
J
≤ +125°C
Package Thermal Resistance
4x4 MLF-16 (θ
JA
) ..............................................30°C/W
Electrical Characteristics(5)
T
A
= 25°C with V
IN
= V
OUT
+ 1V; V
EN
= V
IN
; I
OUT
= 10mA; bold values indicate –40°C ≤ T
J
≤ +125°C, unless noted.
Parameter Conditions Min Typ Max Units
Output Voltage Accuracy 10mA < I
OUT
< I
L(max)
, V
OUT
+ 1 ≤ V
IN
≤ 5.5V -2 +2 %
Feedback Voltage Adjustable version only 0.49 0.50 0.51 V
Feedback Current Adjustable version only 20 nA
Output Voltage Line Regulation V
IN
= V
OUT
+ 1V to 5.0V 0.06 0.5 %
Output Voltage Load Regulation I
L
= 10mA to 3A 0.5 1 %
V
IN
– V
O
; Dropout Voltage I
L
= 1.5A
I
L
= 3.0A
I
L
= 4.0A
300
360
400
500
800
mV
mV
mV
Ground Pin Current I
L
= 10mA
I
L
= 1.5A
I
L
= 3.0A
I
L
= 4.0A
1.2
20
55
90
130
mA
mA
mA
mA
Shutdown Current V
EN
= 0V; V
OUT
= 0V 0.01 10 µA
Current Limit V
OUT
= 0V; V
IN
= 3.0V 4.0 6.0 A
Start-up Time V
EN
= V
IN
; C
RC
= Open 35 150 µs
Enable Input
Enable Input Threshold Regulator enable
Regulator shutdown 1
0.2 V
V
Enable Hysteresis 20 120 200 mV
Enable Input Current V
IL
≤ 0.2V (Regulator shutdown)
V
IH
≥ 1V (Regulator enable) 0.02
3 µA
µA
POR Output
I
POR(LEAK)
V
POR
= 5.5V; POR = High 1
2 µA
µA
V
POR(LO)
Output Logic-Lo w Voltage (undervoltage condition),
I
POR
= 1mA 60
90 mV
7.5 10 12.5 %
Threshold, % of V
OUT
below nominal 10 12.5 15 %
V
POR
:
V
OUT
Ramping Up
V
OUT
Ramping Down
Hysteresis 3 %
Delay Current V
DELAY
= 0.75V 0.7 1 1.3 µA
Delay Voltage (Note 6) V
POR
= High 1.185 1.235 1.285 V
Micrel, Inc. MIC68400
June 2007 7 M9999-061907-B
Parameter Conditions Min Typ Max Units
Ramp Control
I
RC
Ramp Control Current (V
RC
= 0.75V) 0.7 1 1.3 µA
I
DISCHARGE(OUTPUT)
(Note 7) V
OUT
= 0.5V
NOM
, V
RAMP
=0V 25 45 70 mA
Tracking Accuracy: Fixed
(Note 8)
200mV < V
RC
< V
TARGET ;
Measure
(VOUT – V
RC
) -50 25 100 mV
Tracking Accuracy: Adjustable
(Note 8)
Measure
(VOUT -
V
RC
x (V
TARGET
/ 500mV)) -10 15 50 mV
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. The maximum allowable power dissipation of any T
A
(ambient temperature) is P
D(max)
= T
J(max)
– T
A
) / θ
JA
. Exceeding the maximum
allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown.
4. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
5. Specification for packaged product only.
6. Timer High Voltage along with Delay pin current (1µA nom) determines the delay per µF of capacitance. Typical delay is 1.1sec/µF.
7. Discharge current is the current drawn from the output to ground to actively discharge the output capacitor during the shutdown process.
8. V
TARGET
is the output voltage of an adjustable with customer resistor divider installed bet ween V
OUT
and Adj/Sns pin, or the rated output
voltage of a fixed device.
Micrel, Inc. MIC68400
June 2007 8 M9999-061907-B
Typical Characteristics
Micrel, Inc. MIC68400
June 2007 9 M9999-061907-B
Functional Characteristics
Micrel, Inc. MIC68400
June 2007 10 M9999-061907-B
Applications Information
Enable Input
The MIC68400 features a TTL/CMOS compatible
positive logic enable input for on/off control of the
device. High (>1V) enables the regulator while low
(<.2V) disables the regulator. In shutdown the
regulator consumes very little current (only a few
microamperes of leakage). For simple applications the
enable (EN) can be connected to V
IN
(IN). While
MIC68400 only requires a few µA’s of enable current
to turn on, actual enable pin current will depend on the
overdrive (enable voltage exceeding 1V) in each
particular application.
Control Logic
High > 1V
Enable Connections for Logic Driven Input
Enable Connection for V
IN
-Driven
and/or Slow Rise-Time Inputs
Input Capacitor
An input capacitor of 0.1µF or greater is
recommended when the device is more than 4 inches
away from the bulk supply capacitance, or when the
supply is a battery. Small, surface mount chip capac-
itors can be used for the bypassing. The capacitor
should be place within 1 inch of the device for optimal
performance. Larger values will help to improve ripple
rejection by bypassing the regulator input, further
improving the integrity of the output voltage.
Output Capacitor
The MIC68400 requires an output capacitor for stable
operation. As a µCap LDO, the MIC68220 can
operate with ceramic output capacitors of 10µF or
greater with ESR’s ranging from a 3mΩ to over
300mΩ. Values of greater than 10µF improve trans-
ient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their superior temperature
performance. X7R-type capacitors change capaci-
tance by 15% over their operating temperature range
and are the most stable type of ceramic capacitors.
Larger output capacitances can be achieved by
placing tantalum or aluminum electrolytics in parallel
with the ceramic capacitor. For example, a 100µF
electrolytic in parallel with a 10µF ceramic can provide
the transient and high frequency noise performance of
a 100µF ceramic at a significantly lower cost. Specific
undershoot/overshoot performance will depend on
both the values and ESR/ESL of the capacitors.
Micrel, Inc. MIC68400
June 2007 11 M9999-061907-B
Adjustable Regulator Design
Adjustable Regulator with Resistors
The adjustable MIC68400 output voltage can be
programmed from 0.5V to 5.5V using a resistor divider
from output to the SNS pin. Resistors can be quite
large, up to 1MΩ because of the very high input
impedance and low bias current of the sense
amplifier. Typical sense input currents are less than
30nA which causes less than 0.3% error with R1 and
R2 less than or equal to 100KΩ. For large value
resistors (>50KΩ) R1 should be bypassed by a small
capacitor (C
FF
= 0.1µF bypass capacitor) to avoid
instability due to phase lag at the ADJ/SNS input.
The output resistor divider values are calculated by:
⎟
⎠
⎞
⎜
⎝
⎛+= 1
R2
R1
0.5VV
OUT
Power on Reset (POR) and Delay (DLY)
The power-on reset output (POR) is an open-drain
N-Channel device requiring a pull-up resistor to either
the input voltage or output voltage for proper voltage
levels. POR is driven by the internal timer so that the
release of POR at turn-on can be delayed for as much
as 1 second. POR is always pulled low when enable
(EN) is pulled low or the output goes out of regulation
by more than 10% due to loading conditions.
The internal timer is controlled by the DLY pin which
has a bidirectional current source and two limiting
comparators. A capacitor connected from DLY to
GND sets the delay time for two functions. On start
up, DLY sets the time from the nominal output voltage
is reached to the release of the POR. At shut down,
the delay sets the time from disable (EN pin driven
low) to actual ramp down of the output voltage. The
current source is ±1µA, which charges the capacitor
from ~150mV (nominal disabled DLY voltage) to
~1.25V. At turn on, the DLY cap begins to charge
when the output voltage reaches 90% of the target
value. When the capacitor reaches 1.25V, the output
of the POR is released to go high. At turn off, the DLY
cap begins to discharge when the EN is driven low.
When the cap reaches ~150mV the output is ramped
down. Both delays are nominally the same, and are
calculated by the same formula:
()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=A1
C
1.1T
DLY
DLY
µ
Scale Factor is:
1.1 seconds/microfarad,
1.1 milliseconds/nanofarad, or
1.1 microseconds/picofarad.
T
DLYOFF
is the time from lowering of EN to the start of
ramp down on the off cycle. T
POR
is the time from the
rising of EN to the release (low to high edge) of the
POR. This behavior means that a µP or other complex
logic system is guaranteed that the nominal output
voltage is stable for a known time before the POR is
released, and they are further guaranteed that once
POR is pulled low, they have a known time to ‘tidy up’
memory or other registers for a well controlled
shutdown. In Master/Slave configurations the timers
can be used to assure that the Master is always
accurately regulating when the Slave is on.
Ramp Control
The ramp control (RC) has a bidirectional current
source an d a sens e amplifie r, whic h toge ther are used
to control the voltage at the output. When RC is below
the target voltage (nominal output voltage for fixed
voltage parts, 0.5V for adjustable parts) the RC pin
controls the output voltage. When RC is at or above
the target voltage, the output is controlled by the
internal regulator.
Tracking Applications: Driving RC from a Voltage
Source
Fixed Parts: If RC is driven from another (Master)
regulator the two outputs will track each other until the
Master exceeds the target voltage of the Slave
regulator. Typically the output of the MIC68400 will
track above the RC input by 30mV to 70mV. This
offset is designed to allow Master/Slave tracking of
same-voltage regulators. Without the offset, same-
voltage Master/Slave configurations could suffer poor
regulation.
Adjustable Parts: The RC pin on adjustable versions
operates from 0V to 0.5V. To implement tracking on
an adjustable version, an external resistor divider
must be used. This divider is the nearly same ratio as
the voltage setting divider used to drive the
Sense/Adjustable pin. It is recommended that the ratio
be adjusted to track ~50mV (2% to 3%) above the
target voltage if the Master and Slave are operating at
the same target voltage.
Micrel, Inc. MIC68400
June 2007 12 M9999-061907-B
Ramp Up: Cap Controlled Slew Rate
If a capacitor is connected to RC, the bidirectional
current source will charge the cap during startup and
discharge the cap during shutdown. The size of the
capacitor and the RC current (1µA nom) control the
slew rate of the output voltage during startup. For
example, to ramp up a 1.8V regulator from zero to full
output in 10mSec requires a 5.6nF capa citor.
For Fixed Versions:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=A1
C
VT
RC
OUTRC
µ
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
RC
ON
CA1
SR
µ
Similarly, to slew an adjustable (any output voltage)
from 0 to full output in 10mSec requires a 20nF cap.
For Adjustable Version s:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=A1
C
V 5.0T
RC
RC
µ
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
RC
OUTON
CA1
2VSR
µ
Ramp Down: Turn Off Slew Rate
When EN is lowered and the DLY pin has discharged,
the RC pin and the OUT pin slew toward zero. For
fixed voltage devices, the RC pin slew rate is 2 to 3
times the SR
ON
defined above. For adjustable voltage
devices the RC pin slew is much higher. In both
cases, turn off slew rate may be determined by the
RC pin for low values of output capacitor, or by the
maximum discharge current available at the output for
large values of output capacitor. Turn off slew rate is
not a specified characteristic of the MIC68400.
Sequencing Configurations
Sequencing refers to timing based Master/Slave
control between regulators. It allows a Master device
to control the start and stop timing of a single or
multiple Slave devices. In typical sequencing the
Master POR drives the Slave EN. The sequence
begins with the Master EN driven high. The Master
output ramps up and triggers the Master DLY when
the Master output reaches 90%. The Master DLY then
determines when the POR is released to enable the
Slave device. When the Master EN is driven low, the
Master POR is immediately pulled low causing the
Slave to ramp down. However, the Master output will
not ramp down until the Master DLY has fully
discharged. In this way, the Master power can remain
good after the Slave has been ramped down.
In sequencing configurations the Master DLY controls
the turn-on time of the Slave and the Slave DLY
controls the turn-off time of the Slave.
Sequencing Connections
CDlyS > CDlyM [CDlyS=2nF; CDlyM=1nF]
Delayed Sequencing
CDlyS < CDlyM [CDlyS=1nF; CDlyM=2nF]
Windowed Sequencing
Micrel, Inc. MIC68400
June 2007 13 M9999-061907-B
Tracking Configurations
Normal Tracking
In normal tracking the Slave RC pin is driven from the
Master output. The internal control buffering assures
that the output of the Slave is always slightly above
the Master to guarantee that the Slave properly
regulates (based on its own internal reference) if
Master and Slave are both fixed voltage devices of the
same output voltage. The schematic and plot below
show a 1.2 volt device tracking a 1.8 volt device
through the entire turn-on / turn-off sequence. Note
that since the RC pin will overdrive the target voltage
(to assure proper regulation) the ramp down delay is
longer than the POR delay during turn-on.
Fixed Voltage Devices
Fixed voltage versions of MIC68400 have two internal
voltage dividers: one for setting the output voltage and
the other for driving the tracking circuitry. Adjustable
parts have up to two external dividers: one from
output to SNS (to set the output voltage) and one from
the output to the Slave RC pin (in tracking
configurations). Also, the RC pin in fixed parts
operates at the same voltage as the output, whereas
the RC pin in adjustable parts operates at the 0.5V
reference. To setup a normal tracking configuration,
the divider driving the Slave RC pin is the same ratio
(or nearly the same – if both Master and Slave are set
to the same output voltage, the Slave RC divider
should be adjusted 2% to 4% higher) as the divider
driving the Slave SNS pin. This is shown below.
Adjustable Voltage devices
Micrel, Inc. MIC68400
June 2007 14 M9999-061907-B
Ratiometric Tracking
Ratiometric tracking allows independent ramping
speeds for both regulators so that the regulation
voltage is reached at the same time. This is
accomplished by adding a resistor divider between the
Master output pin and the Slave RC pin. The divider
should be scaled such that the Slave RC pin reaches
or exceeds the target output voltage of the Slave as
the Master reaches its target voltage.
Fixed Voltage Devices
Ratiometric tracking may be used with adjustable
parts by simply connecting the RC pins of the Master
and Slave. Use a single RC capacitor of twice the
normal value (since twice the current is injected into
the single RC cap). Alternatively, fixed parts may use
ratiometric tracking in a manner similar to adjustable
normal tracking, with the tracking divider changed to
the same resistor ratio driving the Master Adj/Sns pin.
Adjustable Voltage Devices
Final Note on Tracking
The MIC68400 does not fully shutdown until the output load is discharged to near zero. If RC is driven from an
external source in a tracking configuration, and the external source does not go to zero on shutdown it may prevent
complete shutdown of the MIC68400. This will cause no damage, but some Q current will remain and may cause
concern in battery operated portable equipment. Also, when RC is driven in tracking mode, pulling EN low will not
cause the output to drop. Maintaining low EN in tracking mode simply means that the MIC68400 will shutdown when
the tracking voltage gets near zero. In no case can the MIC68400 enter the tracking mode unless EN is pulled high.
Micrel, Inc. MIC68400
June 2007 15 M9999-061907-B
Package Information
16-Pin 4mm x 4mm MLF (ML)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2007 Micrel, Incorporated.
