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MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
General Description
Benefits and Features
The MAX16956 is a small, synchronous buck converter
with integrated high-side and low-side switches. The device is designed to deliver up to 300mA with input voltages
from 3.5V to 36V, while using only 1.1µA quiescent current
at no load (fixed-output versions). Voltage quality can be
monitored by observing the RESET signal. The device can
operate near dropout by running at 97% duty cycle, making it ideal for automotive applications under cold-crank.
● Integration and High-Switching Frequency Saves
Space
• DC-DC Converter Up to 300mA Capability
• Fixed 5V/3.3V or Programmable Output-Voltage
Options (1V to 15V)
• Current-Mode-Control Architecture
• 2.1MHz Operating Frequency
• Fixed 5.4ms Internal Soft-Start
The device offers fixed-output voltages of 5V and 3.3V, as
well as an adjustable version. The adjustable version allows the user to program the output voltage between 1V
and 15V by using a resistor-divider. Frequency is fixed at
2.1MHz, which allows for small external components, reduced output ripple, and minimized AM radio interference.
The device offers both forced-PWM and skip modes of operation, with ultra-low quiescent current of 1.1µA in skip
mode. The device can be ordered with spread- spectrum
frequency modulation designed to minimize EMI-radiated
emissions due to the switching frequency.
● Spread-Spectrum Frequency Modulation Reduces
EMI Emissions
● Low IQ Enables Designers to Meet Stringent OEM
Module Power-Consumption Requirements
The MAX16956 is available in a small (3mm x 3mm)
10-pin µMAX® package and operates across the full automotive temperature range of -40°C to +125°C. The device
is AEC-Q100 qualified.
● Robust Performance Supports Wide Range of
Automotive Applications
• Short-Circuit, Thermal Protections
• -40°C to +125°C Automotive Temperature Range
• AEC-Q100 Qualified
Applications
● Automotive Body ECUs
● Point-of-Load Applications
● Distributed DC Power Systems
• 1.1μA Quiescent Current in Standby Mode (FixedOutput-Voltage Versions Only)
● Wide Input Voltage Range Supports Automotive
Applications
• Operating VIN Range: 3.5V to 36V (42V Tolerant)
• 97% (Max) Duty-Cycle Operation with Low Dropout
Simplified Block Diagram
VBAT
SUP
BST
CIN
0.1µF
MAX16956
L1
LX
VOUT
COUT
MODE
OUT/FB
EN
BIAS
1µF
RESET
AGND
PGND
μMAX is a registered trademark of Maxim Integrated Products, Inc.
Ordering Information appears at end of data sheet.
19-6737; Rev 6; 2/21
© 2021 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
One Analog Way, Wilmington, MA 01887 U.S.A. | Tel: 781.329.4700 | © 2021 Analog Devices, Inc. All rights reserved.
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Absolute Maximum Ratings
(Voltages Referenced to PGND) ..................................................
SUP ........................................................................ -0.3V to +42V
EN............................................................... -0.3V to VSUP + 0.3V
BST to LX ............................................................................... +6V
BST......................................................................... -0.3V to +47V
MODE, OUT/FB, RESET............................-0.3V to VBIAS + 0.3V
AGND .................................................................... -0.3V to +0.3V
BIAS ...................................................................... -0.3V to +6.0V
OUT/FB Short-Circuit Duration ...................................Continuous
Continuous Power Dissipation (TA = +70°C)
(derate 12.9mW/ºC above +70°C)...............................1031mW
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
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 Information
10 μMAX
Package Code
U10E+3
Outline Number
21-0109
Land Pattern Number
90-0148
THERMAL RESISTANCE, SINGLE-LAYER BOARD
Junction to Ambient (θJA)
77.6°C/W
Junction to Case (θJC)
5°C/W
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.
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.
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.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VSUP = VEN = 14V, VMODE = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless
otherwise noted.) (Note 2)
PARAMETER
Supply Voltage
Supply Current
UV Lockout
www.analog.com
SYMBOL
VSUP
ISUP
CONDITIONS
MIN
TYP
3.5
MAX
36
T < 500ms (Note 3)
42
VEN = 0V
0.75
3.0
No load, fixed 3.3V VOUT
1.1
3.0
No load, fixed 5V VOUT
1.8
5.0
No load, adjustable VOUT
32
70
VMODE = VBIAS , no load, FPWM, no
switching
0.5
1
1.5
VBIAS rising
3.0
3.2
3.4
Hysteresis
0.4
UNITS
V
µA
mA
V
Analog Devices | 2
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Electrical Characteristics (continued)
(VSUP = VEN = 14V, VMODE = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
BIAS Regulator Voltage
VBIAS
VSUP = 5.5V to 36V (MAX16956C/F only)
BIAS Current Limit
MIN
TYP
MAX
5
UNITS
V
10
mA
BUCK CONVERTER
VOUT,5V
VOUT = 5V
6V ≤ VSUP ≤ 36V,
ILOAD = 0 to
300mA
4.9
VOUT = 3.3V
6V ≤ VSUP ≤ 36V,
ILOAD = 0 to
300mA
3.2
3.3
3.4
0.98
1.0
1.03
Voltage Accuracy
VOUT,3.3V
FB Voltage Accuracy
VFB
Adjustable output versions, 6V ≤ VSUP ≤
36V
FB Input Current
IFB
VFB = 1V
5.0
5.2
V
0.02
V
µA
FB Load Regulation
ΔVLOAD
ILOAD = 0.3mA to 300mA
1
%
FB Line Regulation
ΔVLINE
6V ≤ VSUP ≤ 36V
0.02
%/V
High-Side DMOS
RDSON
RON,HS
VBIAS = 5V, ILX = 200mA
1000
2200
mΩ
Low-Side DMOS
RDSON
RON,LS
VBIAS = 5V, ILX = 200mA
500
1200
mΩ
DMOS High-Side
Current-Limit Threshold
IMAX
0.425
0.5
0.575
A
DMOS High-Side SkipMode Peak-Current
Threshold
ISKIP
70
100
130
mA
DMOS Low-Side ZeroCrossing Threshold
IZX
DMOS Low-Side
Negative Current-Limit
Threshold
INEG
Soft-Start Ramp Time
FPWM mode
tSS
mA
-0.320
A
5.4
ms
6
ns
LX Rise Time
tRISE,LX
Minimum On-Time
tON_MIN
60
ns
Maximum Duty Cycle
DCMAX
97
%
PWM Switching
Frequency
fSW
Spread-Spectrum
Range
SS
(Note 3)
40
1.95
2.1
2.25
Spread-spectrum option only
±6
VTHR_RES
VOUT rising
90
92
94
VTHF_RES
VOUT falling
88
90
92
MHz
%
RESET OUTPUT (RESET)
RESET Threshold
RESET Debounce
tDEB
12
%VOUT
µs
RESET High Leakage
Current
ILEAK,RES
TA = +25°C
1
µA
RESET Low Level
VOUT,RES
Sinking 1mA
0.4
V
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Analog Devices | 3
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Electrical Characteristics (continued)
(VSUP = VEN = 14V, VMODE = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
LOGIC LEVELS
EN Input High Threshold
VIH,EN
EN Input Low Threshold
VIL,EN
EN Input Current
IIN,EN
MODE Input High
Threshold
VIH,MODE
MODE Input Low
Threshold
VIL,MODE
MODE Internal Pulldown
RPD,MODE
2.4
V
0.4
0.1
V
µA
1.4
V
0.4
V
1000
kΩ
THERMAL PROTECTION
Thermal Shutdown
TSHDN
(Note 3)
+175
°C
Thermal-Shutdown
Hysteresis
TSHDN,HYS
(Note 3)
+15
°C
Note 2: Limits are 100% tested at TA = +25°C (and/or TA = +125°C). Limits over the operating temperature range and relevant supply
voltage range are guaranteed by design and characterization.
Note 3: Guaranteed by design; not production tested.
Note 4: When the typical minimum on-time of 80ns is violated, the device skips pulses.
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Analog Devices | 4
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Typical Operating Characteristics
(VCC = +3.5V, RSEN = 6.8Ω, TA = +25°C unless otherwise noted.)
80
EFFICIENCY (%)
70
90
60
50
40
60
50
40
70
50
40
30
20
20
20
10
10
10
0
0.000001
0.0001
0.01
0.00001
0.001
IOUT1 (A)
0
0.0001
0.00005
0.0002
0.00015
IOUT1 (A)
0
0.0003
0.00005
0.00025
5V EFFICIENCY v s . L OA D CURRENT
SKIP
90
80
0.0002
0.00015
IOUT1 (A)
0.00025
MAX16956 toc06
VSUP
10V/div
VSUP
10V/div
VOUT
2V/div
60
50
1
0.1
5V FIXED-OUTPUT STA RTUP
WA VEFORMS (SK IP, 300m A L OA D)
MAX16956 toc05
PWM
70
0.0003
3.3V FIXED-OUTPUT STA RTUP
WA VEFORM (PWM, 300m A L OA D)
MAX16956 toc04
100
0.0001
PWM
60
30
0
SKIP
80
30
0
EFFICIENCY (%)
70
90
EFFICIENCY (%)
80
3.3V EFFICIENCY v s . L OA D CURRENT
100
MAX16956 toc02
90
EFFICIENCY (%)
100
MAX16956 toc01
100
5V EFFICIENCY v s . L OA D
CURRENT—SK IP MODE (1μ A t o 300μ A )
MAX16956 toc03
3.3V EFFICIENCY v s . L OA D
CURRENT—SK IP MODE (1μ A t o 300μ A )
VOUT
5V/div
40
30
20
VRESET
5V/div
VRESET
5V/div
VLX
10V/div
VLX
10V/div
10
2ms/div
NO-L OA D SUPPL Y CURRENT
v s . TEMPERA TURE (SK IP MODE)
L OA D REGUL A TION (3.3V OUTPUT)
2.0
1.5
1.0
0.5
L OA D REGUL A TION (5V OUTPUT)
2
PWM
1
0
SKIP
-1
-2
-3
0
-40 -20
0
20
40
60
80 100 120 140
TEMPERATURE (°C)
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3
MAX16956 toc09
VOUT = 3.3V
2.5
OUTPUT-VOLTAGE CHANGE (%)
3
MAX16956 toc07
NO-LOAD SUPPLY CURRENT (μA)
3.0
2ms/div
OUTPUT-VOLTAGE CHANGE (%)
0.1
1
MAX16956 toc08
0
0.000001
0.0001
0.01
0.00001
0.001
IOUT1 (A)
2
PWM
1
0
SKIP
-1
-2
-3
0
0.05
0.10
0.15
0.20
LOAD CURRENT (A)
0.25
0.30
0
0.05
0.10
0.15
0.20
0.25
0.30
LOAD CURRENT (A)
Analog Devices | 5
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Typical Operating Characteristics (continued)
(VCC = +3.5V, RSEN = 6.8Ω, TA = +25°C unless otherwise noted.)
L INE REGUL A TION (3.3V OUTPUT)
L INE REGUL A TION (5V OUTPUT)
2
1
0
-1
-2
ILOAD = 300mA
-3
L OA D-TRA NSIENT RESPONSE
(3.3V, SK IP MODE)
MAX16956 toc11
OUTPUT-VOLTAGE CHANGE (%)
ILOAD = 300mA
3
OUTPUT-VOLTAGE CHANGE (%)
MAX16956 toc10
3
2
MAX16956 toc12
ILOAD
200mA/div
1
0
3.3V
VOUT
100mV/div
AC-COUPLED
3.3V
VPGOOD
5V/div
-1
-2
-3
6
11
16
21
26
31
36
6
INPUT VOLTAGE (V)
11
16
L OA D-TRA NSIENT RESPONSE
(3.3V, PWM MODE)
5V
36
200µs/div
L OA D-TRA NSIENT RESPONSE
(5V, PWM MODE)
MAX16956 toc15
ILOAD
200mA/div
VOUT
5V
50mV/div
AC-COUPLED
VOUT
5V
100mV/div
AC-COUPLED
VOUT
50mV/div
AC-COUPLED
VPGOOD
5V/div
VPGOOD
5V/div
VPGOOD
5V/div
200µs/div
5V
200µs/div
ILOAD
200mA/div
5V
200µs/div
5V FIXED-OUTPUT COL D-CRA NK
RESPONSE (SK IP, NO L OA D)
MAX16956 toc16
3.3V FIXED-OUTPUT DIPS A ND DROPS
RESPONSE (PWM, 300m A L OA D)
MAX16956 toc17
MAX16956 toc18
VSUP
10V/div
VSUP
10V/div
VOUT
2V/div
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31
ILOAD
200mA/div
3.3V FIXED-OUTPUT COL D-CRA NK
RESPONSE (PWM, 300m A L OA D)
400ms/div
26
MAX16956 toc14
MAX16956 toc13
3.3V
21
INPUT VOLTAGE (V)
L OA D-TRA NSIENT RESPONSE
(5V, SK IP MODE)
VSUP
10V/div
VOUT
5V/div
VBIAS
5V/div
VBIAS
5V/div
VLX
10V/div
VLX
10V/div
400ms/div
VOUT
2V/div
VBIAS
5V/div
VLX
10V/div
40ms/div
Analog Devices | 6
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Typical Operating Characteristics (continued)
(VCC = +3.5V, RSEN = 6.8Ω, TA = +25°C unless otherwise noted.)
5V FIXED DIPS A ND DROPS
RESPONSE (SK IP, NO L OA D)
3.3V FIXED-OUTPUT SL OW VSUP
RESPONSE (PWM, NO L OA D)
MAX16956 toc19
MAX16956 toc20
VSUP
10V/div
VSUP
10V/div
VOUT
5V/div
VOUT
2V/div
VOUT
5V/div
VBIAS
5V/div
VBIAS
5V/div
VBIAS
5V/div
VLX
10V/div
VLX
10V/div
VLX
10V/div
10s/div
SHORT-CIRCUIT RESPONSE
(PWM MODE)
MAX16956 toc22
2.10
VLX
10V/div
2.05
3.3V
2.00
VOUT
2V/div
VPGOOD
5V/div
5V
1.95
-40 -20
0
20
40
60
80 100 120 140
1.6
ILX
500mA/div
0A
2.15
2.0
MAX16956 toc23
SHUTDOWN CURRENT (μA)
SWITCHING FREQUENCY (MHz)
2.20
10s/div
SHUTDOWN CURRENT
v s . T E MP E R A T U R E
MAX16956 toc24
40ms/div
VOUT = 3.3V
MAX16956 toc21
VSUP
10V/div
SWITCHING FREQUENCY
v s . TEMPERA TURE
2.25
5V FIXED-OUTPUT SL OW VSUP
RESPONSE (SK IP, NO L OA D)
1.2
0.8
0.4
0
-40 -20
4ms/div
TEMPERATURE (°C)
0
20
40
60
80 100 120 140
TEMPERATURE (°C)
5V FIXED-OUTPUT L OA D-DUMP RESPONSE
(SK IP, VSUP = 13.5V TO 42V, NO L OA D)
MAX16956 toc25
VSUP
10V/div
VOUT
5V/div
VBIAS
5V/div
100ms/div
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Analog Devices | 7
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Pin Configuration
MAX16956
+
BST
1
10
EN
SUP
2
9
OUT/FB
LX
3
8
BIAS
PGND
4
7
MODE
AGND
5
6
RESET
*EXPOSED PAD
MAX16956
*
µMAX
Pin Description
PIN
NAME
1
BST
High-Side Driver Supply. Connect a 0.1μF bootstrap capacitor between LX and BST.
FUNCTION
2
SUP
IC Supply Input. Connect a minimum of 4.7μF ceramic capacitor from SUP to PGND.
3
LX
4
PGND
Power Ground. Connect to AGND under the device in a star configuration.
5
AGND
Analog Ground. Connect to PGND under the device in a star configuration.
6
RESET
Open-Drain Reset Output. An external pullup resistor is required.
7
MODE
Mode Switch-Control Input. Connect to ground or leave open to enable skip-mode operation under
light loads. Connect to BIAS to enable forced-PWM mode. MODE has a 1MΩ internal pulldown.
8
BIAS
Buck Switching Node. LX is high impedance when the device is off.
5V Internal Logic Supply. Connect a 1μF ceramic capacitor to AGND.
MAX16956A/B/D/E (Fixed Output): Buck Regulator Voltage-Sense Input. Bypass OUT to PGND
with a minimum 22μF X7R ceramic capacitor.
9
OUT/FB
MAX16956C/F (Adjustable Output): Feedback Input. Connect FB to a resistive divider between the
buck output and AGND to set the output voltage.
10
EN
SUP Voltage-Compatible Enable Input. Drive EN low to disable the device. Drive EN high to
enable the device.
—
EP
Exposed Pad. Connect EP to a large copper ground plane for effective power dissipation. Do not
use EP as the only IC ground connection. EP must be connected to PGND.
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Analog Devices | 8
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Block Diagram
MODE
HVLDO
EN
BANDGAP
REF
OSC
BIAS
BST
SOFTSTART
MAX16956
LOGIC
CONTROL
OUT/
FB
SUP
CLK
CURRENT SENSE
+
SLOPE COMP
OUT
or FB
OUT
PWM
LX
BIAS
EAMP
FB
SW1
VGOOD
COMP
SW2
PGND
RESET
AGND
Note1: For Internal feedback version SW1 is open and SW2 closed. External pin is called OUT
Note2: For external feedback version SW1 is closed and SW2 is open. External pin is called FB
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Analog Devices | 9
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Detailed Description
The MAX16956 is a small, current-mode buck converter that features synchronous rectification and requires no external
compensation network. The device operates from a 3.5V to 36V supply voltage and can deliver up to 300mA output
current. Frequency is fixed at 2.1MHz, which allows for small external components, reduced output ripple, and
guarantees no AM-band interference.
The device offers fixed output voltages of 5V and 3.3V. The device also offers adjustable output-voltage versions that
can be set by using an external resistive divider. Voltage quality can be monitored by observing the RESET signal. The
device offers both forced-PWM and skip mode, with ultra-low-quiescent cur- rent of 1.1µA in skip mode.
DC-DC Converter Control Architecture
The device step-down converter uses a PWM peak current- mode control scheme, with a load-line architecture. Peak
current-mode control provides several advantages over voltage-mode control, including precise control of the induc- tor
current on a cycle-by-cycle basis, simpler compensa- tion, and inherent compensation for line voltage variation.
An internal transconductance amplifier establishes an integrated error voltage. The heart of the PWM control- ler is an
open-loop comparator: one input is the inte- grated voltage-feedback signal; the other consists of the amplified currentsense signal plus slope-compensation ramp. Integrated high-side current sensing is used, which reduces component
count and layout risk by eliminating the need to carefully route sensitive external signals. Error-amplifier compensation is
also integrated, once again simplifying the power-supply designer’s task while eliminating external components.
At each rising edge of the internal clock, the high-side MOSFET turns on until the PWM comparator trips, the maximum
duty cycle is reached, or the peak current limit is reached (see the Current Limit /Short-Circuit Protection section). During
this on-time, current ramps up through the inductor, storing energy in a magnetic field and sourcing current to the output.
The current-mode feed- back system regulates the peak inductor current as a function of the output-voltage error signal.
During the second-half of the cycle, the high-side MOSFET turns off and the low-side MOSFET turns on. The inductor
releases the stored energy as the current ramps down, providing current to the output. The output capacitor stores
charge when the inductor current exceeds the required load current and discharges when the inductor current is lower,
smoothing the voltage across the load.
The device features load-line architecture to reduce the output capacitance needed, potentially saving system cost and
size. The output voltage is positioned slightly positive at no load, still within the tolerance window, to take advantage of
the fact that any load disturbance is a load step only. This increases the amount of margin available to the undershoot
that occurs on a load step, allowing a reduction in the required output capacitance. As the load increases, a small but
controlled amount
of load regulation (“load-line”) error occurs, so that at heavier loads the voltage is positioned slightly
below nominal. This takes advantage of the fact that any load disturbance is load released, increasing the amount of
margin available to the overshoot that occurs.
The device can operate in either forced-PWM or skip mode. In forced-PWM mode, the converter maintains a constant
switching frequency, regardless of load, to allow for easier filtering of the switching noise. The device includes proprietary
circuitry that dramatically reduces quiescent current consumption in skip mode, improving light-load efficiency. See the
Forced PWM/Skip Modes section for further details.
System Enable (EN)
An enable control input (EN) activates the device from its low-power shutdown mode. EN is compatible with inputs from
automotive battery level down to 3.5V. The high-voltage compatibility allows EN to be connected to SUP, KEY/KL30, or
the inhibit pin (INH) of a CAN transceiver.
Linear Regulator Output (BIAS)
The device includes a 5V linear regulator output (BIAS) that provides power to the internal circuit blocks. Connect a 1µF
ceramic capacitor from BIAS to AGND. Do not load this pin externally.
Undervoltage Lockout
When VBIAS drops below the undervoltage-lockout (UVLO) level of VUVLO = 2.8V (typ), the device assumes that the
supply voltage is too low for proper operation, so the UVLO circuitry inhibits switching. When VBIAS rises above the
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Analog Devices | 10
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
UVLO rising threshold, the controller enters the startup sequence and then resumes normal operation.
Startup and Soft-Start
The device features an internal soft-start timer. The output-voltage soft-start ramp time is 5.4ms (typ). If a short circuit
or undervoltage is encountered after the soft- start timer has expired, the device is disabled for 13.4ms (typ) and then
reattempts soft-start again. This pattern repeats until the short circuit has been removed.
RESET Output
The device features an open-drain RESET output to monitor the output voltage. The RESET output requires an external
pullup resistor. RESET goes high (high impedance) after the regulator output increases above 92% of the nominal
regulated voltage. RESET goes low when the regulator output drops to below 90% of the nominal regulated voltage.
Forced PWM/Skip Modes
The device features a logic-level input (MODE) to switch between forced-PWM and skip modes. Connecting MODE to
BIAS enables the forced-PWM operation. Connecting MODE to ground, or leaving unconnected, enables skip-mode
operation with ultra-low-quiescent current of 1.1µA. In skip-mode operation, the converter’s switching frequency is load
dependent until the output load reaches the skip threshold. At higher load current, the switching frequency does not
change and the operating mode is similar to the forced-PWM mode. Skip mode helps improve efficiency in light-load
applications by allowing the converter to turn on the high-side switch only when the output voltage falls below a set
threshold. As such, the converter does not switch the MOSFETs on and off as often as is the case in the forced-PWM
mode. Consequently, the gate charge and switching losses are much lower in skip mode.
Current Limit /Short-Circuit Protection
The device has fault protection designed to protect itself from abnormal conditions. If the output is soft shorted (meaning
the output is overloaded but over 50% of regulation), cycle-by-cycle current limit limits how high the inductor current goes
for any cycle. If the output is hard shorted to ground and the output falls to less than 50% of regulation, the part goes into
a mode where it switches until 15 cycles are ended by current limit, then waits for 13.4ms before trying to soft-start again.
This mode of operation limits the amount of power dissipated by the device under these conditions. The device also has
overtemperature protection. If the die temperature exceeds approximately 175°C, the device stops switching until the die
temperature drops by approximately 15°C and then resumes operation, including going through soft-start again.
Spread-Spectrum Option
The device has an internal spread-spectrum option to optimize EMI performance. This is factory set on the D, E, and
F variants of the device. For spread-spectrum-enabled variants of the device, the operating frequency is varied ±6%
centered on 2.1MHz. The modulation signal is a triangular wave with a period of 230µs at 2.1MHz. Therefore, fSW ramps
down 6% and back to 2.1MHz in 115µs and also ramps up 6% and back to 2.1MHz in 115µs. The cycle repeats.
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Analog Devices | 11
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Applications Information
Setting the Output Voltage
The device’s adjustable output-voltage version (see the Selector Guide for more details) allows the user to set the output
to any voltage between 1V and 15V. Connect a resistive divider from output (VOUT) to FB to AGND to set the output
voltage (Figure 1). Select R2 (FB to AGND resistor) less than or equal to 100kΩ. Calculate R1 (VOUT to FB resistor) with
the following equation
VOUT
R1 = R2 × [( V
) − 1]
FB
where VFB = 1V (see the Electrical Characteristics).
VOUT
MAX16956
R1
FB
R2
Figure 1. Adjustable Output-Voltage Setting
Inductor Selection
Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor saturation
current (ISAT), and DC resistance (RDCR). To select inductance value, the ratio of inductor peak-to-peak AC current to
DC average current (LIR) must be selected first. A good compromise between size and loss is a 30% peak-to-peak ripple
current to average current ratio (LIR = 0.3). The switching frequency, input voltage, output voltage, and selected LIR then
determines the inductor value as follows:
VOUT × (VSUP − VOUT)
L= V
SUP × fSW × IOUT × LIR
where VSUP, VOUT, and IOUT are typical values (so that efficiency is optimum for typical conditions). The switching
frequency is 2.1MHz. Table 1 lists some of the inductor values for 300mA output current and several output voltages.
Input Capacitor
The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the
input caused by the circuit’s switching. The input capacitor RMS current requirement (IRMS) is defined by the following
equation:
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Analog Devices | 12
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
IRMS = ILOAD(MAX) √
VOUT × (VSUP − VOUT)
VSUP
IRMS has a maximum value when the input voltage equals twice the output voltage (VSUP = 2VOUT), so IRMS(MAX) =
ILOAD(MAX)/2. Choose an input capacitor that exhibits less than +10°C self-heating temperature rise at the RMS input
current for optimal long-term reliability.
Table 1. Inductor Values for 300mA Output Current
VSUP/VOUT (V)
14V/5V
14V/3.3V
INDUCTOR (µH) ILOAD = 300mA
10µH (typ) 22µH (max)
10µH (typ) 22µH (max)
The input voltage ripple is composed of ΔVQ (caused by the capacitor discharge) and ΔVESR (caused by the ESR of the
capacitor). Use low-ESR ceramic capacitors with high ripple current capability at the input. Assume the contribution from
the ESR and capacitor discharge equal to 50%. Calculate the input capacitance and ESR required for a specified input
voltage ripple using the following equations:
△ VESR
ESRIN =
IOUT +
∆ IL
2
where:
∆ IL =
(VSUP − VOUT) × VOUT
VSUP × fSW × L
and:
CIN =
IOUT × D(1 − D)
∆ VQ × fSW
VOUT
and D = V
SUP
where IOUT is the maximum output current and D is the duty cycle.
Output Capacitor
The output filter capacitor must have low enough ESR to meet output ripple and load transient requirements. The
output capacitance must be high enough to absorb the inductor energy while transitioning from full-load to noload
conditions. When using high-capacitance, low-ESR capacitors, the filter capacitor’s ESR dominates the output voltage
ripple. Therefore, the size of the output capacitor depends on the maximum ESR required to meet the output voltage
ripple (VRIPPLE(P-P)) specifications:
VRIPPLE(P−P) = ESR×ILOAD(MAX)×LIR
The actual capacitance value required relates to the physical size needed to achieve low ESR, as well as to the chemistry
of the capacitor technology. Therefore, the capacitor is usually selected by ESR and voltage rating rather than by
capacitance value. When using low-capacity filter capacitors, such as ceramic capacitors, size is usually determined by
the capacity needed to prevent voltage droop and voltage rise from causing problems during load transients. Generally,
once enough capacitance is added to meet the overshoot requirement, undershoot at the rising-load edge is no longer a
problem.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low-switching power losses and clean, stable operation. Use a multi- layer board
whenever possible for better noise immunity and power dissipation. Follow these guidelines for good PCB layout:
1. The input capacitor (4.7μF, see Figures 3 and 4) should be placed immediately next to the SUP pin of the device.
Since the device operates at 2.1MHz switching frequency, this placement is critical for effective decoupling of highfrequency noise from the SUP pin.
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 sides. 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 path from the sensitive analog circuitry. Doing so is essential to
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Analog Devices | 13
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
prevent any noise coupling into the analog signals.
4. Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free
operation.
5. Connect PGND and AGND together 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.
7. Place the BIAS capacitor ground next to the AGND pin and connect with a short and wide trace.
Table 2. SELECTOR GUIDE
PART
MAX16956AUBA+
MAX16956AUBA/ V+
VOUT
RESET TIME
(µs)
SPREAD SPECTRUM
PIN-PACKAGE
TOP MARK
Fixed 5V
10
Off
10 µMAX-EP
+AABX
Fixed 5V
10
Off
10 µMAX-EP
+AABH
MAX16956AUBB+
Fixed 3.3V
10
Off
10 µMAX-EP
+AABY
MAX16956AUBB/ V+
Fixed 3.3V
10
Off
10 µMAX-EP
+AABI
MAX16956AUBC +
Adjustable
10
Off
10 µMAX-EP
+AABZ
MAX16956AUBC / V+
Adjustable
10
Off
10 µMAX-EP
+AABJ
MAX16956AUBD / V+
Fixed 5V
10
On
10 µMAX-EP
+AABK
MAX16956AUBE/ V+
Fixed 3.3V
10
On
10 µMAX-EP
+AABL
MAX16956AUBF/ V+
Adjustable
10
On
10 µMAX-EP
+AABM
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Analog Devices | 14
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Typical Application Circuits
MAX16956AUBA/V+ (5.0V Fixed) and MAX16956AUBB/V+ (3.3V Fixed), 10-Pin μMAX
VBAT
CIN1
4.7µF
MAX16956
SUP
BST
CBST
0.1µF
CIN2
0.1µF
L
10µH
LX
NH
VOUT
3.3V/5V
MODE
OUT
EN
COUT
22µF
NL
BIAS
RESET
AGND
PGND
CBIAS
1µF
MAX16956AUBC/V+, Variable Output Voltage, 10-Pin μMAX
VBAT
CIN1
4.7µF
MAX16956
SUP
BST
CBST
0.1µF
CIN2
0.1µF
L
10µH
VOUT
1V-15V
LX
NH
RTOP
VARIES
MODE
COUT
22µF
FB
EN
BIAS
RESET
AGND
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RBOT
50kΩ
NL
PGND
CBIAS
1µF
Analog Devices | 15
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX16956AUB_ +
PART
-40°C to +125°C
10 µMAX-EP*
MAX16956AUB_ / V+
-40°C to +125°C
10 µMAX-EP*
Note: Insert the desired suffix letter (from the Selector Guide) into the blank to indicate the output voltage and spread-spectrum
option.
/ V denotes an automotive qualified part.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
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Analog Devices | 16
MAX16956
36V, 300mA, Mini Buck Converter with 1.1μA IQ
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/13
Initial release
1
2/14
Changed PGND to AGND for pin 8 in the Pin Description section, removed C1 from
Figure 1, and added nonautomotive OPNs for MAX16956A, MAX16956B, and
MAX16956C versions
2
3/14
Removed future product references
15
3
2/15
Updated the Benefits and Features section
1
4
8/15
Updated Block Diagram
9
5
10/15
Added top marks to Selector Guide
15
6
2/21
Increasing the output voltage range to 15V.
DESCRIPTION
PAGES
CHANGED
—
8, 11, 15
1,2,10,11,14
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is
assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may
result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of
their respective owners.
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Analog Devices | 17
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