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
operate 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 frequency 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
●Wide +3.5V to +28V Input Voltage Range
●Tolerates Input Voltage Transients to +42V
●600mA Minimum Output Current with Overcurrent
Protection
●Fixed Output Voltages (See the Selector Guide and
Contact Factory for All Available Trimmed Output
Voltage Options)
● 2.1MHz Switching Frequency with Three Modes
of Operation
• 25μA Ultra-Low Quiescent Current SKIP Mode
• Forced Fixed-Frequency Operation
• External Frequency Synchronization
● Optional Spread-Spectrum Frequency Modulation
●Power-Good Output
● Enable-Pin Compatible from +3.3V Logic Level
to +42V
●Thermal Shutdown Protection
●-40°C to +125°C Automotive Temperature Range
●10-Pin TDFN-EP or 16-Pin TSSOP-EP Packages
● AEC-Q100 Qualified
Selector Guide appears at end of data sheet.
19-5481; Rev 12; 11/15
Note: Insert the desired suffix letters (from Selector Guide)
into the blanks to indicate the output voltage.
Alternative output voltages available upon request.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*EP = Exposed pad.
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Ordering Information
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*
EVALUATION KIT AVAILABLE
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
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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Typical Operating Circuits
(Voltages referenced to GND.)
SUP, EN..................................................................-0.3V to +42V
BST to LX (Note 1)....................................................-0.3V to +6V
LX (Note 1)................................................-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
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
(Note 2)
(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
Supply Voltage Range VSUP (Note 3) 3.5 28 V
t < 1s 42
Supply Current ISUP
EN = low 4 8 µA
EN = high, no load, 3V < VOUT < 5.5V 25 35
EN = high, continuous, no switching 1 mA
UV Lockout VUVLO Bias rising 2.8 3 3.2 V
VUVLO,HYS Hysteresis 0.4
Bias Voltage VBIAS +5.5V ≤ VSUP ≤ +42V 5 V
Bias Current Limit IBIAS 10 mA
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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Note 1: Self protected against transient voltages exceeding these limits for ≤ 50ns under normal operation and loads up to the maxi-
mum rated output current.
Note 2: 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.maximintegrated.com/thermal-tutorial.
Absolute Maximum Ratings
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.
Package Thermal Characteristics
Electrical Characteristics
(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
BUCK CONVERTER
Voltage Accuracy
VOUT
VOUT = 5V, xed frequency
6V ≤ VSUP ≤ 18V,
ILOAD = 0 to
600mA, TA =
-40°C to +125°C
-2.0% +2.5%
V
VOUT = 5V, SKIP mode (Note 4) -2.0% +4.0%
VOUT,3.3V
VOUT = 3.3V, xed frequency -2.0% 3.3 +2.5%
VOUT = 3.3V, SKIP mode (Note 4) -2.0% 3.3 +4.0%
VOUT,5V
VOUT = 5V, xed frequency -2.0% 5 +2.5%
VOUT = 5V, SKIP mode (Note 4) -2.0% 5 +4.0%
VOUT,5.1V
VOUT = 5.1V, xed frequency -2.0% 5.1 +2.5%
VOUT = 5.1V, SKIP mode (Note 4) -2.0% 5.1 +4.0%
VOUT,5.5V
VOUT = 5.5V, xed frequency -2.0% 5.5 +2.5%
VOUT = 5.5V, SKIP mode (Note 4) -2.0% 5.5 +4.0%
VOUT,6.0V
VOUT = 6.0V, xed frequency -2.0% 6.0 +2.5%
VOUT = 6.0V, SKIP mode (Note 4) -2.0% 6.0 +4.0%
VOUT,8.0V
VOUT = 8.0V, xed frequency -2.0% 8.0 +2.5%
VOUT = 8.0V, SKIP mode (Note 4) -2.0% 8.0 +4.0%
SKIP-Mode Peak Current ISKIP 350 mA
High-Side DMOS RDSON RON,HS VBIAS = 5V 400 800 mΩ
Low-Side DMOS RDSON RON,LS 250 450 mΩ
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 %
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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Electrical Characteristics (continued)
Note 3: When the typical minimum on-time of 80ns is violated, the device skips pulses.
Note 4: Guaranteed by design; not production tested.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
PGOOD
PGOOD Threshold VTHR,PGD VOUT rising 88 93 98 %
VTHF,PGD VOUT falling 88 91 94
PGOOD Debounce tDEB 10 µs
PGOOD High Leakage
Current ILEAK,PGD TA = +25°C, VPGD ≤ VOUT 1 µA
PGOOD Output Low Level VOUT,PGD Sinking 1mA 0.4 V
LOGIC LEVELS
EN Level VIH,EN 2.4 V
VIL,EN 0.6
EN Input Current IIN,EN VEN = VSUP = +42V, TA = +25°C 1 µA
SYNC Switching Threshold VIH,SYNC 1.4 V
VIL,SYNC 0.4
SYNC Internal Pulldown RPD,SYNC 200 kΩ
THERMAL PROTECTION
Thermal Shutdown TSHDN 175 °C
Thermal Shutdown
Hysteresis TSHDN,HYS 15 °C
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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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.)
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
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
6 28
5V PART
3.3V PART
LINE REGULATION
(ILOAD = 600mA)
MAX16904 toc03
INPUT VOLTAGE (V)
OUTPUT VOLTAGE CHANGE (%)
26248 10 12 16 18 2014 22
-3
-2
-1
0
1
2
3
4
-4
6 28
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
0 0.6
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
6 28
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
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
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MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Typical Operating Characteristics
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
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
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MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Typical Operating Characteristics (continued)
PIN NAME FUNCTION
TDFN-EP TSSOP-EP
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.
611 PGOOD Open-Drain Power-Good Output.
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.
611PGND PGOOD
314SUP GND
215SUP EN
116BST N.C.
512LX SYNC
4
TSSOP
13LX BIAS
EP
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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Pin Description
Pin Congurations
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
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Functional Diagram
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 output
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 compat-
ible 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 programmable 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 internal
undervoltage lockout level VUVLO = 3V (typ).
Soft-Start
The device features an internal soft-start timer. The output
voltage soft-start ramp time is 8ms (typ). If a short circuit
or undervoltage is encountered, after the softstart 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 Efciency
(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 switching 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 (val-
ley) drops below the 1.2V (typ) feedback voltage.
Achieving High Efciency 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 current 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
standby mode. In this mode, the majority of the internal
circuitry (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 frequency
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 inductor, 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
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If the input voltage is reduced and the device approaches
dropout, it tries to turn on the high-side FET continu-
ously. 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 frequency
varies by +6% relative to the internally generated operat-
ing frequency of 2.1MHz (typ). Spread spectrum is offered
to improve EMI performance of the device. By varying the
frequency 6% only in the positive 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 generated
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 immedi-
ately 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
The nominal inductor value can be calculated using Table
based on the nominal output voltage of the device. Select
the nearest standard inductance value to the calculated
nominal value. The nominal standard value selected
should be within ±25% of LNOM for best performance.
Input Capacitor
A low-ESR ceramic input capacitor of 1μF or larger is
needed for proper device operation. This value may need
to be larger based on application input ripple requirements.
The discontinuous input current of the buck converter
causes large input ripple current. The switching frequency,
peak inductor current, and the allowable peak-to-peak
input-voltage ripple dictate the input capacitance require-
ment. 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 ΔVQ (caused by the
capacitor discharge) and ΔVESR (caused by the ESR of
the input capacitor). The total voltage ripple is the sum of
ΔVQ and ΔVESR. Assume the input-voltage ripple from
the ESR and the capacitor discharge is equal to 50%
each. The following equations show the ESR and capaci-
tor requirement for a target voltage ripple at the input:
Table 1. Inductor Selection
Table 2. Examples for Standard
Output Voltages
VOUT (V) LNOM (µH)
1.8 to 3.1 VOUT/0.55
3.2 to 6.5 VOUT/0.96
6.6 to 8.1 VOUT/1.40
8.2 to 10 VOUT/1.75
VOUT
(V)
CALCULATED
LNOM (µH)
STANDARD
VALUE (µH)
1.8 3.3 3.3
3.3 3.4 3.3
5.0 5.2 4.7
8.0 5.7 5.6
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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ESR
PP
OUT
OUT
IN Q SW
V
ESR I
I2
I D ( 1 D )
CV f
−
∆
=∆

+


×−
=∆×
where:
IN OUT OUT
PP
IN SW
( V V ) V
IV f L
−
−×
∆= ××
and:
OUT
IN
V
DV
=
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 possible
undershoot below the UVLO threshold during transient
loading.
Output Capacitor
To maintain acceptable phase margin, a minimum ceram-
ic output capacitor value of 10μF is needed with a volt-
age rating of 2 times the VOUT voltage. Additional output
capacitance may be needed based on application-specific
output voltage ripple requirements.
The allowable output-voltage ripple and the maximum devi-
ation of the output voltage during step load currents deter-
mine the output capacitance and its ESR. The output ripple
comprises of ΔVQ (caused by the capacitor discharge) and
ΔVESR (caused by the ESR of the output capacitor). Use
low-ESR ceramic or aluminum electrolytic capacitors at
the output. For aluminum electrolytic capacitors, the entire
output ripple is contributed by ΔVESR. Use the ESROUT
equation to calculate 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 require-
ment for a specified output-voltage ripple.
ESR
PP
PP
OUT
Q SW
V
ESR I
I
C8V f
−
−
∆
=∆
∆
=×∆ ×
where:
IN OUT OUT
PP IN SW
OUT_RIPPLE ESR Q
(V V ) V
IV f L
V VV
−
−×
∆= ××
≅∆ +∆
ΔIP-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 capacitance 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 converter. The device’s high switching
frequency allows for a higher closed-loop bandwidth, thus
reducing tRESPONSE and the output capacitance require-
ment. 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 tantalum and
ceramic capacitors for better transient load and ripple/noise
performance. Keep the maximum output-voltage devia-
tions 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 follow-
ing equations to calculate the required ESR and capaci-
tance value:
ESR
OUT STEP
STEP RESPONSE
OUT
Q
V
ESR I
I t
CV
∆
=
×
=∆
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 sche-
matic 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.
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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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 ambient,
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 out-
put 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 con-
nect 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 Figure 2. Machine Model 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
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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PART OUTPUT VOLTAGE
(V) PIN-PACKAGE SPREAD-SPECTRUM
SWITCHING FREQUENCY
TOP
MARK
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
MAX16904RATB33+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) — AZR
MAX16904RATB50+ 5.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm) —AYG
MAX16904RATB55/V+** 5.5 10 TDFN-EP*
(3mm x 3mm x 0.75mm) —AYL
MAX16904RAUE33+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16904RAUE50+ 5.0 16 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16904SATB33+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AZS
MAX16904SATB41/V+** 4.1 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes BAC
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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│
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Selector Guide
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.
PART OUTPUT VOLTAGE
(V) PIN-PACKAGE SPREAD-SPECTRUM
SWITCHING FREQUENCY
TOP
MARK
MAX16904SATB50+ 5.0 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AZT
MAX16904SATB55/V+ 5.5 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes BAG
MAX16904SAUE33+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) Yes —
MAX16904SAUE50+ 5.0 16 TSSOP-EP*
(5mm x 4.4mm) Yes —
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
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
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│
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Selector Guide (continued)
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.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.
Chip Information
PROCESS: BiCMOS
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/10 Initial release —
1 11/10 Added new output voltage trim to Selector Guide 12
23/11 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
37/11 Added the MAX16904RATB50+ part number to the Selector Guide 13
43/12 Added new future part numbers to the Selector Guide 13
56/12 Updated Selector Guide to include MAX16904SATB51/V+ and the MAX16904SATB52/V+ 13
64/13 Updated Pin Description, Inductor Selection, Input Capacitor, Output Capacitor, and
Selector Guide sections
1, 7, 10,
11, 13
78/13 Added limits for 5.1V, 6V, and 8V options in Electrical Characteristics and update Selector
Guide 3, 13, 14
812/13 Added condition for Supply Current and Voltage Accuracy in Electrical Characteristics and
removed future product indicator from MAX16904SATB52/V+ 2, 13
99/14 Updated Typical Operating Circuit and PGOOD high leakage current conditions in
Electrical Characteristics 2, 4
10 3/15 Added new Note 1 in Absolute Maximum Ratings section and renumbered remaining notes
in Package Thermal Characteristics and Electrical Characteristics sections 3, 4
11 9/15 Added VOUT 5.5V parts to Electrical Characteristics and Selector Guide tables; updated
PGOOD Threshold min/max values in Electrical Characteristics table 3, 4, 13, 14
12 11/15 Removed future product reference to MAX16904SATB55/V+ in Selector Guide 15
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications 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.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2015 Maxim Integrated Products, Inc.
│
16
MAX16904 2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Revision History
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MAX16904RATB50+T MAX16904SATB51/V+T MAX16904SATB60/V+T MAX16904SATB80/V+T
MAX16904RAUE18/V+ MAX16904RAUE18/V+T MAX16904SATB41/V+T MAX16904SATB52/V+T
MAX16904RATB33/V+ MAX16904SAUE33+ MAX16904RAUE50+ MAX16904RAUE33+