General Description
The MAX16904 is a small, synchronous buck converter
with integrated high-side and low-side switches. The
device is designed to deliver 600mA with input voltages
from +3.5V to +28V while using only 25µA quiescent
current at no load. Voltage quality can be monitored by
observing the PGOOD signal. The MAX16904 can oper-
ate in dropout by running at 97% duty cycle, making it
ideal for automotive and industrial applications.
The MAX16904 operates at a 2.1MHz frequency, allow-
ing for small external components and reduced output
ripple. It guarantees no AM band interference. SYNC
input programmability enables three frequency modes
for optimized performance: forced fixed-frequency
operation, SKIP mode (ultra-low quiescent current of
25µA), and synchronization to an external clock. The
MAX16904 can be ordered with spread-spectrum fre-
quency modulation, designed to minimize EMI-radiated
emissions due to the modulation frequency.
The MAX16904 is available in a thermally enhanced,
3mm x 3mm, 10-pin TDFN package or a 16-pin TSSOP
package. The MAX16904 operates over the -40°C to
+125°C automotive temperature range.
Applications
Automotive
Industrial
Military
High-Voltage Input-Power DC-DC Applications
Features
oWide +3.5V to +28V Input Voltage Range
oTolerates Input Voltage Transients to +42V
o600mA Minimum Output Current with Overcurrent
Protection
oFixed Output Voltages (+3.3V and +5V)
o2.1MHz Switching Frequency with Three Modes of
Operation
25µA Ultra-Low Quiescent Current SKIP Mode
Forced Fixed-Frequency Operation
External Frequency Synchronization
oOptional Spread-Spectrum Frequency Modulation
oPower-Good Output
oEnable-Pin Compatible from +3.3V Logic Level to
+42V
oThermal Shutdown Protection
o-40°C to +125°C Automotive Temperature Range
o10-Pin TDFN-EP or 16-Pin TSSOP-EP Packages
oAEC-Q100 Qualified
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
1
19-5481; Rev 5; 6/12
EVALUATION KIT
AVAILABLE
PART SPREAD
SPECTRUM
TEMP
RANGE
PIN-
PACKAGE
MAX16904RATB__/V+ Disabled -40°C to
+125°C 10 TDFN-EP*
MAX16904RAUE__/V+ Disabled -40°C to
+125°C 16 TSSOP-EP*
MAX16904SATB__/V+ Enabled -40°C to
+125°C 10 TDFN-EP*
MAX16904SAUE__/V+ Enabled -40°C to
+125°C 16 TSSOP-EP*
Ordering Information
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Note: Insert the desired suffix letters (from
Selector Guide
) into
the blanks to indicate the output voltage. Alternative output volt-
ages available upon request.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*
EP = Exposed pad.
Selector Guide appears at end of data sheet.
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
2
MAX16904_50/V+
20kΩ
2.2µF
33kΩ
EN
SYNC
GND
VBAT LEVEL
SIGNAL
PGOOD
BIAS
SUP
*PLACE INPUT SUPPLY CAPACITORS AS CLOSE AS POSSIBLE TO THE SUP PIN. SEE THE APPLICATIONS INFORMATION SECTION FOR MORE DETAILS.
4.7µF
BST
0.1µF
4.7µH
LX
10µF
PGND
5V AT 600mA
OUTS
MAX16904_33/V+
20kΩ
2.2µF
33kΩ
EN
SYNC
GND
VBAT LEVEL
SIGNAL
PGOOD
BIAS
SUP
4.7µF
BST
0.1µF
*
*
3.3µH
LX
10µF
PGND
3.3V AT 600mA
OUTS
Typical Operating Circuits
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
3
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VSUP = +14V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
(Voltages referenced to GND.)
SUP, EN..................................................................-0.3V to +42V
BST to LX..................................................................-0.3V to +6V
LX..............................................................-0.3V to (VSUP + 0.3V)
BST .........................................................................-0.3V to +47V
OUTS ......................................................................-0.3V to +12V
SYNC, PGOOD, BIAS............................................-0.3V to +6.0V
PGND to GND .......................................................-0.3V to +0.3V
LX Continuous RMS Current .................................................1.0A
OUTS Short-Circuit Duration ......................................Continuous
ESD Protection
Human Body Model .........................................................±2kV
Machine Model ..............................................................±200V
Continuous Power Dissipation (TA= +70°C)
TDFN (derate 24.4 mW/°C above +70°C)......................1951mW
TSSOP (derate 26.1 mW/°C above +70°C) ...................2089mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PACKAGE THERMAL CHARACTERISTICS (Note 1)
TDFN
Junction-to-Ambient Thermal Resistance (θJA) ...........41°C/W
Junction-to-Case Thermal Resistance (θJC) ..................9°C/W
TSSOP
Junction-to-Ambient Thermal Resistance (θJA) ........38.3°C/W
Junction-to-Case Thermal Resistance (θJC) ..................3°C/W
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
(Note 2) 3.5 28
Supply Voltage Range VSUP t < 1s 42 V
EN = low 4 8
EN = high, no load 25 35 µA
Supply Current ISUP
EN = high, continuous, no switching 1 mA
VUVLO Bias rising 2.8 3 3.2
UV Lockout VUVLO,HYS Hysteresis 0.4 V
Bias Voltage VBIAS +5.5V VSUP +42V 5 V
Bias Current Limit IBIAS 10 mA
BUCK CONVERTER
VOUT = 5V, fixed frequency -2.0% 5 +2.5%
VOUT,5V VOUT = 5V, SKIP mode
(Note 3) -2.0% 5 +4%
VOUT = 3.3V, fixed frequency -2.0% 3.3 +2.5%
Voltage Accuracy
VOUT,3.3V VOUT = 3.3V, SKIP mode
(Note 3)
6V VSUP 18V,
ILOAD = 0 to 600mA,
TA = -40°C to
+125°C
-2.0% 3.3 +4%
V
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
4
ELECTRICAL CHARACTERISTICS (continued)
(VSUP = +14V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SKIP-Mode Peak Current ISKIP 350 mA
High-Side DMOS RDSON R
ON,HS V
BIAS = 5V 400 800 m
Low-Side DMOS RDSON R
ON,LS 250 450 m
DMOS Peak Current-Limit
Threshold IMAX 0.85 1.05 1.22 A
Soft-Start Ramp Time tSS 7 8 9 ms
LX Rise Time tRISE,LX 5 ns
Minimum On-Time tON 80 ns
PWM Switching Frequency fSW Internally generated 1.925 2.1 2.275 MHz
SYNC Input Frequency Range fSYNC 1.8 2.6 MHz
Spread-Spectrum Range SS Spread-spectrum option only +6 %
PGOOD
VTHR,PGD V
OUT rising 93
PGOOD Threshold VTHF,PGD V
OUT falling 88 91 94 %
PGOOD Debounce tDEB 10 µs
PGOOD High Leakage Current ILEAK,PGD T
A = +25°C 1 µA
PGOOD Output Low Level VOUT,PGD Sinking 1mA 0.4 V
LOGIC LEV EL S
VIH,EN 2.4
EN Level VIL,EN 0.6 V
EN Input Current IIN,EN V
EN = VSUP = +42V, TA = +25°C 1 µA
VIH,SYNC 1.4
SYNC Switching Threshold VIL,SYNC 0.4 V
SYNC Internal Pulldown RPD,SYNC 200 k
THERMAL PROTECTION
Thermal Shutdown TSHDN 175 °C
Thermal Shutdown Hysteresis TSHDN,HYS 15 °C
Note 2: When the typical minimum on-time of 80ns is violated, the device skips pulses.
Note 3: Guaranteed by design; not production tested.
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
5
Typical Operating Characteristics
(VSUP = +14V, TA= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
MAX16904 toc01
LOAD CURRENT (A)
EFFICIENCY (%)
0.50.40.30.20.1
10
20
30
40
50
60
70
80
90
100
0
0 0.6
5V, SKIP MODE
5V, FFF MODE
3.3V, FFF MODE
3.3V, SKIP MODE
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE (SKIP MODE)
MAX16904 toc02
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
2624222018161412108
10
20
30
40
50
60
0
628
5V PART
3.3V PART
LINE REGULATION
(ILOAD = 600mA)
MAX16904 toc03
INPUT VOLTAGE (V)
OUTPUT VOLTAGE CHANGE (%)
2624810 12 16 18 2014 22
-3
-2
-1
0
1
2
3
4
-4
628
LOAD REGULATION
MAX16904 toc04
LOAD CURRENT (A)
OUTPUT-VOLTAGE CHANGE (%)
0.50.40.1 0.2 0.3
-3
-2
-1
0
1
2
3
4
-4
00.6
SKIP MODE
FFF MODE
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX16904 toc05
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
2624222018161412108
3
6
9
12
15
0
628
STARTUP RESPONSE
(ILOAD = 600mA)
MAX16904 toc06
1ms/div
VEN
5V/div
IL
1A/div
VOUT
5V/div
VPGOOD
5V/div
SHUTDOWN WAVEFORM (ILOAD = 600mA)
MAX16904 toc07
IINDUCTOR
0.5A/div
PGOOD
5V/div
VOUT
5V/div
EN
5V/div
20µs/div
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
6
LOAD TRANSIENT RESPONSE
(3.3V, FIXED MODE)
MAX16904 toc08
40µs/div
600mA
IL
500mA/div
100mA
VOUT
50mV/div
AC-COUPLED
5V
VBIAS
5V/div
5V
VPGOOD
5V/div
LOAD TRANSIENT RESPONSE
(3.3V, SKIP MODE)
MAX16904 toc09
40µs/div
600mA
IL
500mA/div
100mA
VOUT
50mV/div
AC-COUPLED
5V
VBIAS
5V/div
5V
VPGOOD
5V/div
LOAD TRANSIENT RESPONSE
(5V, FIXED MODE)
MAX16904 toc10
40µs/div
600mA
IL
500mA/div
100mA
VOUT
50mV/div
AC-COUPLED
5V
VBIAS
5V/div
5V
VPGOOD
5V/div
LOAD TRANSIENT RESPONSE
(5V, SKIP MODE)
MAX16904 toc11
40µs/div
600mA
IL
500mA/div
100mA
VOUT
50mV/div
AC-COUPLED
5V
VBIAS
5V/div
5V
VPGOOD
5V/div
UNDERVOLTAGE PULSE
(COLD CRANK)
MAX16904 toc12
10ms/div
VSUP
10V/div
VOUT
5V/div
ILOAD
500mA/div
VPGOOD
5V/div
STANDBY CURRENT
vs. LOAD CURRENT
MAX16904 toc13
ILOAD (mA)
IIN (µA)
0.1
50
100
150
200
250
300
350
400
450
500
0
0.01 1
Typical Operating Characteristics (continued)
(VSUP = +14V, TA= +25°C, unless otherwise noted.)
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
7
Pin Description
PIN
TDFN-EP TSSOP-EP
NAME FUNCTION
1 1 BST Bootstrap Capacitor for High-Side Driver (0.1µF)
2 2, 3 SUP
Voltage Supply Input. Connect a 4.7µF ceramic capacitor from SUP to PGND. Place the
capacitor very close to the SUP pin. For the TSSOP-EP package, connect both SUP pins
together for proper operation.
3 4, 5 LX
Buck Switching Node. LX is high impedance when the device is off. For the TSSOP
package, connect both LX pins together for proper operation.
4 6, 7 PGND
Power Ground. For the TSSOP-EP package, connect both PGND pins together for proper
operation.
5 8 OUTS
Buck Regulator Voltage-Sense Input. Bypass OUTS to PGND with a 10µF or larger X7R
ceramic capacitor.
6 11 PGOOD
Open-Drain Power-Good Output. External pullup resistor required for automatic SKIP
mode operation.
7 12 SYNC
Sync Input. SYNC allows the device to synchronize to other supplies. When connected
to GND or unconnected, SKIP mode is enabled under light loads. When connected to a
clock source or BIAS, forced PWM mode is enabled.
8 13 BIAS +5V Internal Logic Supply. Connect a 2.2µF ceramic capacitor from BIAS to GND.
9 14 GND Analog Ground
10 15 EN Enable Input. EN is high-voltage compatible. Drive EN HIGH for normal operation.
9, 10, 16 N.C. No Connection. Not internally connected.
EP Exposed Pad. Connect EP to PGND. Do not use EP as the only ground connection.
MAX16904
+
5 6OUTS PGOOD
4
TOP VIEW
7PGND SYNC
38LX BIAS
29SUP GND
1
TDFN
10BST EN
EP
MAX16904
+
8 9OUTS N.C.
710PGND N.C.
6 11PGND PGOOD
314SUP GND
215SUP EN
116BST N.C.
512LX SYNC
4
TSSOP
13LX BIAS
EP
Pin Configurations
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
8
Functional Diagram
MAX16904
LSD
PWM
EAMP
COMP
HSD
BIAS
LX
PGND
BST
SUP
LOGIC
CONTROL
CURRENT-SENSE
AND
SLOPE COMPENSATION
SOFT-START
OSCBANDGAP
GND
VGOOD
PGOOD
OUTS
BIAS
HVLDO
SYNC
REF
EN
CLK
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
9
Detailed Description
The MAX16904 is a small, current-mode buck converter
that features synchronous rectification and requires no
external compensation network. The device is designed
for 600mA output current, and can stay in dropout by
running at 97% duty cycle. It provides an accurate out-
put voltage within the +6.5V to +18V input range.
Voltage quality can be monitored by observing the
PGOOD signal. The device operates at 2.1MHz (typ)
frequency, which allows for small external components,
reduced output ripple, and guarantees no AM band
interference.
The device features an ultra-low 25µA (typ) quiescent
supply current in standby mode. Standby mode is
entered when load currents are below 5mA and when
SYNC is low. The device operates from a +3.5V to
+28V supply voltage and tolerates transients up to
+42V, making it ideal for automotive applications. The
device is available in factory-trimmed output voltages
from 1.8V to 10.7V in 100mV steps. Contact the factory
for availability of voltage options.
Enable (EN)
The device is activated by driving EN high. EN is com-
patible from a +3.3V logic level to automotive battery
levels. EN can be controlled by microcontrollers and
automotive KEY or CAN inhibit signals. The EN input
has no internal pullup/pulldown current to minimize
overall quiescent supply current. To realize a program-
mable undervoltage lockout level, use a resistor-
divider from SUP to EN to GND.
BIAS/UVLO
The device features undervoltage lockout. When the
device is enabled, an internal bias generator turns on.
LX begins switching after VBIAS has exceeded the inter-
nal undervoltage lockout level VUVLO = 3V (typ).
Soft-Start
The device features an internal soft-start timer. The out-
put voltage soft-start ramp time is 8ms (typ). If a short
circuit or undervoltage is encountered, after the soft-
start timer has expired, the device is disabled for 30ms
(typ) and it reattempts soft-start again. This pattern
repeats until the short circuit has been removed.
Oscillator/Synchronization and
Efficiency (SYNC)
The device has an on-chip oscillator that provides a
switching frequency of 2.1MHz (typ). Depending on the
condition of SYNC, two operation modes exist. If SYNC
is unconnected or at GND, the device must operate in
highly efficient pulse-skipping mode if the load current
is below the SKIP mode current threshold. If SYNC is at
BIAS or has a frequency applied to it, the device is in
forced PWM mode. The device offers the best of both
worlds. The device can be switched during operation
between forced PWM mode and SKIP mode by switch-
ing SYNC.
SKIP Mode Operation
SKIP mode is entered when the SYNC pin is connected
to ground or is unconnected and the peak load current
is < 350mA (typ). In this mode, the high-side FET is
turned on until the current in the inductor is ramped up
to 350mA (typ) peak value and the internal feedback
voltage is above the regulation voltage (1.2V typ). At
this point, both the high-side and low-side FETs are
turned off. Depending on the choice of the output
capacitor and the load current the high-side FET turns
on when OUTS (valley) drops below the 1.2V (typ) feed-
back voltage.
Achieving High Efficiency at Light Loads
The device operates with very low quiescent current at
light loads to enhance efficiency and conserve battery
life. When the device enters SKIP mode the output cur-
rent is monitored to adjust the quiescent current.
When the output current is < 5mA, the device operates in
the lowest quiescent current mode also called the stand-
by mode. In this mode, the majority of the internal circuit-
ry (excluding that necessary to maintain regulation) in the
device, including the internal high-voltage LDO, is turned
off to save current. Under no load and with SKIP mode
enabled, the device draws only 25µA (typ) current. For
load currents > 5mA, the device enters normal SKIP
mode while still maintaining very high efficiency.
Controlled EMI with Forced-Fixed Frequency
In forced PWM mode, the device attempts to operate at
a constant switching frequency for all load currents. For
tightest frequency control, apply the operating frequen-
cy to SYNC. The advantage of this mode is a constant
switching frequency, which improves EMI performance;
the disadvantage is that considerable current can be
thrown away. If the load current during a switching
cycle is less than the current flowing through the induc-
tor, the excess current is diverted to GND. With no
external load present, the operating current is in the
10mA range.
Extended Input Voltage Range
In some cases, the device is forced to deviate from its
operating frequency independent of the state of SYNC.
For input voltages above 18V, the required duty cycle
to regulate its output may be smaller than the minimum
on-time (80ns, typ). In this event, the device is forced to
lower its switching frequency by skipping pulses.
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
10
If the input voltage is reduced and the device
approaches dropout, it tries to turn on the high-side
FET continuously. To maintain gate charge on the high-
side FET, the BST capacitor must be periodically
recharged. To ensure proper charge on the BST
capacitor when in dropout, the high-side FET is turned
off every 6.5µs and the low-side FET is turned on for
about 150ns. This gives an effective duty cycle
of > 97% and a switching frequency of 150kHz when in
dropout.
Spread-Spectrum Option
The device has an optional spread-spectrum version. If
this option is selected, then the internal operating fre-
quency varies by +6% relative to the internally generat-
ed operating frequency of 2.1MHz (typ). Spread
spectrum is offered to improve EMI performance of the
device. By varying the frequency 6% only in the posi-
tive direction, the device still guarantees that the
2.1MHz frequency does not drop into the AM band limit
of 1.8MHz. Additionally, with the low minimum on-time
of 80ns (typ) no pulse skipping is observed for a 5V
output with 18V input maximum battery voltage in
steady state.
The internal spread spectrum does not interfere with
the external clock applied on the SYNC pin. It is active
only when the device is running with internally generat-
ed switching frequency.
Power-Good (PGOOD)
The device features an open-drain power-good output.
PGOOD is an active-high output that pulls low when the
output voltage is below 91% of its nominal value.
PGOOD is high impedance when the output voltage is
above 93% of its nominal value. Connect a 20kΩ(typ)
pullup resistor to an external supply or the on-chip BIAS
output.
Overcurrent Protection
The device limits the peak output current to 1.05A (typ).
To protect against short-circuit events, the device shuts
off when OUTS is below 1.5V (typ) and one overcurrent
event is detected. The device attempts a soft-start
restart every 30ms and stays off if the short circuit has
not been removed. When the current limit is no longer
present, it reaches the output voltage by following the
normal soft-start sequence. If the device die reaches
the thermal limit of +175°C (typ) during the current-limit
event, it immediately shuts off.
Thermal-Overload Protection
The device features thermal-overload protection. The
device turns off when the junction temperature exceeds
+175°C (typ). Once the device cools by 15°C (typ), it
turns back on with a soft-start sequence.
Applications Information
Inductor Selection
Three key inductor parameters must be specified for
operation with the device: inductance value (L), peak
inductor current (IPEAK), and inductor saturation current
(ISAT). The minimum required inductance is a function
of operating frequency, input-to-output voltage differen-
tial, and the peak-to-peak inductor current
(∆IP-P). Higher ∆IP-P allows for a lower inductor value,
while a lower ∆IP-P requires a higher inductor value. A
lower inductor value minimizes size and cost, improves
large-signal and transient response, but reduces effi-
ciency due to higher peak currents and higher peak-to-
peak output-voltage ripple for the same output
capacitor. On the other hand, higher inductance
increases efficiency by reducing the ripple current.
Resistive losses due to extra wire turns can exceed the
benefit gained from lower ripple current levels especial-
ly when the inductance is increased without also allow-
ing for larger inductor dimensions. A good compromise
is to choose ∆IP-P equal to 30% of the full load current.
Use the following equation to calculate the inductance:
VIN and VOUT are typical values so that efficiency is
optimum for typical conditions. The switching frequency
is ~2.1MHz. The peak-to-peak inductor current, which
reflects the peak-to-peak output ripple, is worse at the
maximum input voltage. See the
Output Capacitor
sec-
tion to verify that the worst-case output ripple is accept-
able. The inductor saturation current is also important to
avoid runaway current during continuous output short
circuit. The output current may reach 1.22A since this is
the maximum current limit. Choose an inductor with a
saturation current of greater than 1.22A to ensure prop-
er operation and avoid runaway.
Input Capacitor
The discontinuous input current of the buck converter
causes large input ripple current. The switching frequen-
cy, peak inductor current, and the allowable peak-to-
peak input-voltage ripple dictate the input capacitance
requirement. Increasing the switching frequency or the
inductor value lowers the peak-to-average current ratio
yielding a lower input capacitance requirement.
The input ripple comprises mainly of ∆VQ(caused by
the capacitor discharge) and ∆VESR (caused by the
LVVV
Vf I
OUT IN OUT
IN SW P P
=−
××
−
()
∆
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
11
ESR of the input capacitor). The total voltage ripple is
the sum of ∆VQand ∆VESR. Assume the input-voltage
ripple from the ESR and the capacitor discharge is
equal to 50% each. The following equations show the
ESR and capacitor requirement for a target voltage rip-
ple at the input:
where:
and:
where IOUT is the output current, D is the duty cycle,
and fSW is the switching frequency. Use additional
input capacitance at lower input voltages to avoid pos-
sible undershoot below the UVLO threshold during tran-
sient loading.
Output Capacitor
The allowable output-voltage ripple and the maximum
deviation of the output voltage during step load cur-
rents determine the output capacitance and its ESR.
The output ripple comprises of ∆VQ(caused by the
capacitor discharge) and ∆VESR (caused by the ESR of
the output capacitor). Use low-ESR ceramic or alu-
minum electrolytic capacitors at the output. For alu-
minum electrolytic capacitors, the entire output ripple is
contributed by ∆VESR. Use the ESROUT equation to cal-
culate the ESR requirement and choose the capacitor
accordingly. If using ceramic capacitors, assume the
contribution to the output ripple voltage from the ESR
and the capacitor discharge to be equal. The following
equations show the output capacitance and ESR
requirement for a specified output-voltage ripple.
where:
∆IP-P is the peak-to-peak inductor current as calculated
above and fSW is the converter’s switching frequency.
The allowable deviation of the output voltage during
fast transient loads also determines the output capaci-
tance and its ESR. The output capacitor supplies the
step load current until the converter responds with a
greater duty cycle. The response time (tRESPONSE)
depends on the closed-loop bandwidth of the convert-
er. The device’s high switching frequency allows for a
higher closed-loop bandwidth, thus reducing
tRESPONSE and the output capacitance requirement.
The resistive drop across the output capacitor’s ESR
and the capacitor discharge causes a voltage droop
during a step load. Use a combination of low-ESR tan-
talum and ceramic capacitors for better transient load
and ripple/noise performance. Keep the maximum out-
put-voltage deviations below the tolerable limits of the
electronics being powered. When using a ceramic
capacitor, assume an 80% and 20% contribution from
the output capacitance discharge and the ESR drop,
respectively. Use the following equations to calculate
the required ESR and capacitance value:
where ISTEP is the load step and tRESPONSE is the
response time of the converter. The converter response
time depends on the control-loop bandwidth.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
power losses and clean stable operation. Use a multilayer
board wherever possible for better noise immunity. Refer
to the MAX16904 Evaluation Kit for recommended PCB
layout. Follow these guidelines for a good PCB layout:
1) The input capacitor (4.7µF, see the applications
schematic in the
Typical Operating Circuits
) should be
placed right next to the SUP pins (pins 2 and 3 on the
TSSOP-EP package). Because the device operates at
2.1MHz switching frequency, this placement is critical
for effective decoupling of high-frequency noise from
the SUP pins.
ESR V
I
CIt
V
OUT ESR
STEP
OUT STEP RESPONSE
Q
=
=×
∆
∆
∆IVV V
Vf L
V
PP IN OUT OUT
IN SW
OUT RIPPLE
−=−×
××
()
_≅≅+∆∆VV
ESR Q
ESR V
I
CI
Vf
ESR
PP
OUT PP
QSW
=
=××
−
−
∆
∆
∆
∆8
DV
V
OUT
IN
=
∆IVV V
Vf L
PP IN OUT OUT
IN SW
−=−×
××
()
ESR V
II
CIDD
ESR
OUT PP
IN OUT
=
+
⎛
⎝
⎜⎞
⎠
⎟
=×−
−
∆
∆
2
1( ))
∆Vf
QSW
×
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
12
2) Solder the exposed pad to a large copper plane
area under the device. To effectively use this copper
area as heat exchanger between the PCB and ambi-
ent, expose the copper area on the top and bottom
side. Add a few small vias or one large via on the
copper pad for efficient heat transfer. Connect the
exposed pad to PGND ideally at the return terminal
of the output capacitor.
3) Isolate the power components and high current
paths from sensitive analog circuitry.
4) Keep the high current paths short, especially at the
ground terminals. The practice is essential for stable
jitter-free operation.
5) Connect the PGND and GND together preferably at
the return terminal of the output capacitor. Do not
connect them anywhere else.
6) Keep the power traces and load connections short.
This practice is essential for high efficiency. Use
thick copper PCB to enhance full load efficiency and
power dissipation capability.
7) Route high-speed switching nodes away from sensi-
tive analog areas. Use internal PCB layers as PGND
to act as EMI shields to keep radiated noise away
from the device and analog bypass capacitor.
ESD Protection
The device’s ESD tolerance is rated for Human Body
Model and Machine Model. The Human Body Model
discharge components are CS= 100pF and RD= 1.5kΩ
(Figure 1). The Machine Model discharge components
are CS= 200pF and RD= 0Ω(Figure 2).
Figure 1. Human Body ESD Test Circuit
STORAGE
CAPACITOR
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
1MΩ
RD
1.5kΩ
CS
100pF
STORAGE
CAPACITOR
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
RD
0Ω
CS
200pF
Figure 2. Machine Model ESD Test Circuit
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
13
Chip Information
PROCESS: BiCMOS
Selector Guide
PART OUTPUT VOLTAGE
(V) PIN-PACKAGE SPREAD-SPECTRUM
SWITCHING FREQUENCY
TOP
MARK
MAX16904RATB50+ 5.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
⎯AYG
MAX16904RATB50/V+ 5.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
⎯AVY
MAX16904RAUE50/V+ 5.0 16 TSSOP-EP*
(5mm x 4.4mm) ⎯⎯
MAX16904SATB50/V+ 5.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AWA
MAX16904SATB51/V+†5.1 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AYX
MAX16904SATB52/V+†5.2 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AYY
MAX16904SAUE50/V+ 5.0 16 TSSOP-EP*
(5mm x 4.4mm) Yes ⎯
MAX16904RATB33/V+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
⎯AVX
MAX16904RAUE33/V+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) ⎯⎯
MAX16904SATB33/V+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AVZ
MAX16904SAUE33/V+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) Yes ⎯
MAX16904RAUE18/V+†1.8 16 TSSOP-EP*
(5mm x 4.4mm) ⎯⎯
MAX16904SATB60/V+†6.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AYO
MAX16904SATB80/V+†8.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes AYN
Note: All devices operate over the -40°C to +125°C automotive temperature range.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*
EP = Exposed pad.
†
Future product–contact factory for availability.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP T1033+1 21-0137 90-0003
16 TSSOP-EP U16E+3 21-0108 90-0120
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in
the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
14
_______________Maxim Integrated Products, Inc. 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/10 Initial release —
1 11/10 Added new output voltage trim to Selector Guide 12
2 3/11 Updated the Voltage Accuracy and the DMOS Peak Current-Limit Threshold parameters
in the Electrical Characteristics, updated TOCs 1, 6, and 8–13 3, 4, 5, 6
3 7/11 Added the MAX16904RATB50+ part number to the Selector Guide 13
4 3/12 Added new future part numbers to the Selector Guide 13
5 6/12 Updated Selector Guide to include MAX16904SATB51/V+ and the MAX16904SATB52/V+ 13
