MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
General Description
The MAX16930/MAX16931 offer two high-voltage,
synchronous step-down controllers and a step-up
preboost controller. They operate with an input voltage
supply from 2V to 42V with preboost active and can
“operate in drop-out condition by running at 95% duty
cycle. The devices are intended for applications with
mid- to high-power requirements that operate at a wide
input voltage range such as during automotive coldcrank or engine stop-start conditions.
The MAX16930/MAX16931 step-down controllers
operate 180° out-of-phase at frequencies up to 2.2MHz
to allow small external components, reduced output
ripple, and to guarantee no AM band interference. The
switching frequency is resistor adjustable. The FSYNC
input programmability enables three frequency modes
for optimized performance: forced fixed-frequency
operation, skip mode with ultra-low quiescent
current (20µA), and synchronization to an external clock.
The devices also provide a spread-spectrum option to
minimize EMI interference.
The MAX16930/MAX16931 are offered with an
asynchronous step-up controller. This preboost circuitry turns on during low input voltage conditions. It is
designed to provide power to step-down controller channels with input voltages as low as 2V.
The devices also feature a power-OK monitor and
overvoltage and undervoltage lockout. Protection
features include cycle-by-cycle current limit and thermal
shutdown.
The devices are available in 40-pin TQFN-EP and
side-wettable QFND-EP packages and are specified
for operation over the -40°C to +125°C automotive
temperature range.
Benefits and Features
●● Meets Stringent OEM Module Power Consumption
and Performance Specifications
• 20µA Quiescent Current in Skip Mode
• ±1% Output-Voltage Accuracy: 5.0V/3.3V Fixed or
Adjustable Between 1V and 10V
●● Enables Crank-Ready Designs
• Integrated Preboost for Operation Down to 2V in
Bootstrap Mode
• Wide Input Supply Range from 3.5V to 36V
(without Preboost)
●● EMI Reduction Features Reduce Interference with
Sensitive Radio Bands without Sacrificing Wide Input
Voltage Range
• 50ns (typ) Minimum On-Time Guarantees SkipFree Operation for 3.3V Output from Car Battery
at 2.2MHz
• Frequency-Synchronization Input
• Resistor-Programmable Frequency Between
200kHz and 2.2MHz
●● Integration and Thermally Enhanced Packages Save
Board Space and Cost
• Dual, 2MHz Step-Down Controllers
• 180° Out-of-Phase Operation
• Current-Mode Controllers with Forced-Continuous
and Skip Modes
• Thermally Enhanced 40-Pin TQFN-EP and
Side-Wettable QFND-EP Packages
●● Protection Features Improve System Reliability
• Supply Overvoltage and Undervoltage Lockout
• Overtemperature and Short-Circuit Protection
Applications
POL Applications for Automotive Power
Distributed DC Power Systems
Navigation and Radio Head Units
Selector Guide and Ordering Information appear at end of
data sheet.
19-6631; Rev 13; 7/16
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Absolute Maximum Ratings
IN, INS, CS3P, CS3N, FB3, EN1, EN2,
EN3, TERM to PGND_........................................-0.3V to +42V
CS1, CS2, OUT1, OUT2 to AGND.........................-0.3V to +11V
CS1 to OUT1.........................................................-0.2V to +0.2V
CS2 to OUT2.........................................................-0.2V to +0.2V
CS3P to CS3N.......................................................-0.2V to +0.2V
BIAS, FSYNC, FOSC to AGND..............................-0.3V to +6.0V
COMP1, COMP2, BSTON to AGND......................-0.3V to +6.0V
FB1, FB2, FSELBST, EXTVCC to AGND...............-0.3V to +6.0V
DL_ to PGND_ (Note 1).........................................-0.3V to +6.0V
BST_ to LX_ (Note 1)............................................-0.3V to + 6.0V
DH_ to LX_ (Note 1).............................................-0.3V to + 6.0V
LX_ to PGND_ (Note 1)..........................................-0.3V to +42V
PGND_ to AGND...................................................-0.3V to +0.3V
PGOOD1, PGOOD2 to AGND..............................-0.3V to +6.0V
Continuous Power Dissipation (TA = +70NC)
TQFN (derate 37mW/NC above +70NC).....................2963mW
QFND (derate 29.4mW/NC above +70NC)..................2350mW
Operating Temperature Range......................... -40NC to +125NC
Junction Temperature Range...........................................+150NC
Storage Temperature Range............................. -65NC to +150NC
Lead Temperature (soldering, 10s).................................+300NC
Soldering Temperature (reflow).......................................+260NC
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 (Note 2)
TQFN
Junction-to-Ambient Thermal Resistance (qJA)...........27°C/W
Junction-to-Case Thermal Resistance (qJC)..................1°C/W
QFND
Junction-to-Ambient Thermal Resistance (qJA)...........34°C/W
Junction-to-Case Thermal Resistance (qJC)...............3.9°C/W
Note 1: Self-protected against transient voltages exceeding these limits for ≤ 50ns under normal operation and loads up to the
maximum 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.
Electrical Characteristics
(VIN = 14V, VBIAS = 5V, CBIAS = 6.8µF, TA = TJ = -40NC to +125NC, unless otherwise noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNIT
SYNCHRONOUS STEP-DOWN DC-DC CONVERTERS
Normal operation
Supply Voltage Range
Supply Current
VIN
IIN
Buck 1 Fixed Output Voltage
VOUT1
Buck 2 Fixed Output Voltage
VOUT2
Output Voltage Adjustable
Range
www.maximintegrated.com
3.5
36
t < 1s
With preboost after initial startup condition
is satisfied
42
2.0
VEN1 = VEN2 = VEN3 = 0V
8
20
VEN1 = 5V, VOUT1 = 5V, VEN2 = VEN3 =
0V, VEXTVCC = 5V, no switching
30
40
VEN2 = 5V, VOUT2 = 3.3V, VEN1 = VEN3 =
0V, VEXTVCC = 3.3V, no switching
20
30
VEN1 = VEN2 = 5V, VOUT1 = 5V, VOUT2 =
3.3V, VEN3 = 0V, VEXTVCC = 3.3V,
no switching
25
40
VFB1 = VBIAS, PWM mode
4.95
5
5.05
VFB1 = VBIAS, skip mode
4.95
5
5.075
VFB2 = VBIAS, PWM mode
3.234
3.3
3.366
VFB2 = VBIAS, skip mode
3.234
3.3
3.4
Buck 1, buck 2
1
V
36
10
FA
V
V
V
Maxim Integrated │ 2
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Electrical Characteristics (continued)
(VIN = 14V, VBIAS = 5V, CBIAS = 6.8µF, TA = TJ = -40NC to +125NC, unless otherwise noted.) (Note 3)
PARAMETER
Regulated Feedback Voltage
SYMBOL
Output Overvoltage Threshold
Feedback Leakage Current
IFB1,2
Feedback Line Regulation Error
Transconductance
(from FB_ to COMP_)
gm
Dead Time
Maximum Duty-Cycle
Minimum On-Time
MIN
TYP
MAX
UNIT
0.99
1.0
1.01
V
FB rising
+10
+15
+20
FB falling (Note 4)
+5
+10
+15
TA = +25NC
0.01
1
VIN = 3.5V to 36V, VFB = 1V
0.00
VFB = 1V, VBIAS = 5V (Note 5)
1200
MAX16930, DL_ low to DH_ high
35
MAX16930, DH_ low to DL_ high
60
MAX16931, DL_ low to DH_ high
60
MAX16931, DH_ low to DL_ high
100
Buck 1, buck 2
tON(MIN)
PWM Switching Frequency
Range
fSW
Spread-Spectrum Range
%
FA
%/V
2400
FS
ns
95
Buck 1, buck 2
50
%
ns
Programmable, high frequency,
MAX16930
1
2.2
Programmable, low frequency,
MAX16931
0.2
1
MHz
MAX16930ATLT/V+,
MAX16930BATLU/V+ only
Buck 2 Switching Frequency
Switching Frequency Accuracy
CONDITIONS
VFB1,2
1/2fSW
MHz
MAX16930, RFOSC = 13.7kI,
VBIAS = 5V
1.98
2.2
2.42
MHz
MAX16931, RFOSC = 80.6kI,
VBIAS = 5V
360
400
440
kHz
Spread spectrum enabled
±6
%
FSYNC INPUT
FSYNC Frequency Range
FSYNC Switching Thresholds
CS Current-Limit Voltage
Threshold
Minimum sync pulse of 100ns, MAX16930
1.2
2.4
MHz
Minimum sync pulse of 100ns, MAX16931
240
1200
kHz
High threshold
1.5
Low threshold
VLIMIT1,2
VCS - VOUT, VBIAS = 5V, VOUT R 2.5V
Skip Mode Threshold
Current sense = 80mV
Soft-Start Ramp Time
Buck 1 and buck 2, fixed soft-start time
regardless of frequency
Phase Shift Between Buck1 and
Buck 2
64
80
96
15
2
6
VIN = 6V, VLX_ = VIN, TA = +25NC
DH1, DH2 Pullup Resistance
DH1, DH2 Pulldown Resistance
V
mV
mV
10
180
LX1, LX2 Leakage Current
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0.6
ms
°
0.01
1
FA
VBIAS = 5V, IDH_ = -100mA
10
20
I
VBIAS = 5V, IDH_ = +100mA
2
4
I
Maxim Integrated │ 3
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Electrical Characteristics (continued)
(VIN = 14V, VBIAS = 5V, CBIAS = 6.8µF, TA = TJ = -40NC to +125NC, unless otherwise noted.) (Note 3)
TYP
MAX
UNIT
DL1, DL2 Pullup Resistance
PARAMETER
VBIAS = 5V, IDL_ = -100mA
4
8
I
DL1, DL2 Pulldown Resistance
VBIAS = 5V, IDL_ = +100mA
1.5
3
I
PGOOD1, PGOOD2 Threshold
SYMBOL
CONDITIONS
MIN
PGOOD_H
% of VOUT_, rising
85
90
95
PGOOD_F
% of VOUT_, falling
80
85
90
0.01
1
PGOOD1, PGOOD2 Leakage
Current
VPGOOD1,2 = 5V, TA = +25NC
PGOOD1, PGOOD2 Startup
Delay Time
Buck 1 and buck 2 after soft-start
is complete
PGOOD1, PGOOD2 Debounce
Time
Fault detection
64
8
%
FA
Cycles
20
40
Fs
5
5.25
V
3.1
3.4
INTERNAL LDO: BIAS
Internal BIAS Voltage
VIN > 6V
4.75
VBIAS rising
BIAS UVLO Threshold
VBIAS falling
2.7
Hysteresis
External VCC Threshold
2.9
0.2
VTH,EXTVCC
EXTVCC rising, HYST = 110mV
3
V
V
3.2
V
THERMAL OVERLOAD
Thermal Shutdown Temperature
(Note 5)
170
NC
Thermal Shutdown Hysteresis
(Note 5)
20
NC
EN LOGIC INPUT
High Threshold
1.8
V
Low Threshold
Input Current
0.01
EN1, EN2 logic inputs only, TA = +25NC
0.8
V
1
FA
PREBOOST
Minimum On Time
TONBST
60
ns
Minimum Off Time
TOFFBST
60
ns
VFSELBST = 0V, RFOSC = 13.7kI
1.98
2.2
2.42
VFSELBST = VBIAS, RFOSC = 13.7kI
0.4
0.44
0.48
ILIMBST
CS3P - CS3N
108
120
132
mV
VINS,UV
One-time latch during startup; preboost
is disabled until the VINS rises above
this threshold (MAX16930ATLV/V+,
MAX16930BATLW/V+ (Note 6))
1
1.05
1.1
V
Switching Frequency
fBOOST
Current Limit
INS Unlock Threshold
www.maximintegrated.com
MHz
Maxim Integrated │ 4
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Electrical Characteristics (continued)
(VIN = 14V, VBIAS = 5V, CBIAS = 6.8µF, TA = TJ = -40NC to +125NC, unless otherwise noted.) (Note 3)
PARAMETER
INS Off Threshold
INS On Threshold
INS Threshold
Undervoltage Lockout
SYMBOL
VINS,OFF
VINS,ON,SW
CONDITIONS
MIN
TYP
MAX
Battery rising and EN3 high, preboost
turns off if VINS is above this threshold
(MAX16930ATLV/V+, MAX16930BATLW/
V+ (Note 6))
1.2
1.25
1.3
Battery falling and EN3 high, preboost
turns back on when VINS falls below
this threshold (MAX16930ATLV/V+,
MAX16930BATLW/V+ (Note 6))
1.1
1.15
1.2
0.325
0.35
0.375
Battery rising and EN3 high
(MAX16930ATLV/V+, MAX16930BATLW/
V+ (Note 6))
VINS,UV
Battery falling and EN3 high, preboost
turns off when VINS falls below this
threshold (MAX16930ATLV/V+,
MAX16930BATLW/V+ (Note 6))
UNIT
V
V
0.275
0.3
0.325
0.01
1
BSTON Leakage Current
VBSTON = 5V, TA = +25NC
BSTON Debounce Time
Fault detection
10
DL3 Pullup Resistance
VBIAS = 5V, IDL3 = -100mA
4
8
I
DL3 Pulldown resistance
VBIAS = 5V, IDL3 = +100mA
1
2
I
1.25
1.3125
V
Feedback Voltage
Boost Load Regulation Error
EN3 Threshold
VFB3
No load on boost output
1.1875
0mV < VCS3P - VCS3N < 120mV,
error proportional to input current
High threshold
Fs
0.7
%/A
3.5
Low threshold
FA
2
V
EN3 Input Current
VEN3 = 5.5V
7
14
FA
TERM Resistance
ITERM = 10mA
70
150
I
TERM Leakage Current
VTERM = 14V, VEN3 = 0V, TA = +25NC
0.01
1
FA
INS and FB3 Leakage Current
TA = +25NC
0.01
1
FA
Note 3: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range and relevant supply voltage are guaranteed by design and characterization. Typical values are at TA = +25°C.
Note 4: Overvoltage protection is detected at the FB1/FB2 pins. If the feedback voltage reaches overvoltage threshold of FB1/FB2
+ 15% (typ), the corresponding controllers stop switching. The controllers resume switching once the output drops below
FB1/FB2 + 10% (typ).
Note 5: Guaranteed by design; not production tested.
Note 6: INS pin functionality is disabled for the MAX16930ATLV/V+, MAX16930BATLW/V+. EN3 directly controls the turn-on and
turn-off of the boost controller.
www.maximintegrated.com
Maxim Integrated │ 5
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
NO-LOAD STARTUP SEQUENCE
(VFSYNC = 0V)
MAX16930 toc01
FULL-LOAD STARTUP SEQUENCE
(VFSYNC = 0V)
MAX16930 toc02
VBAT
5V/div
VOUT1
2V/div
IOUT1
2A/div
VPGOOD1
5V/div
VOUT2
2V/div
IOUT2
2A/div
VPGOOD2
5V/div
VOUT1
2V/div
VOUT2
2V/div
VPGOOD1
5V/div
VPGOOD2
5V/div
4ms/div
VEN1 = 0V
VEN2 = VBAT
EXTVCC = VOUT2
10
70
60
50
40
30
MAX16930 toc04
BUCK 1
EXTVCC = VOUT2
40
30
20
0
20 40 60 80 100 120 140
80
5
10
15
70
60
EXTVCC =
GND
SKIP MODE
50
30
PWM MODE
10
20
25
30
35
EXTVCC =
GND
EXTVCC =
VOUT1
40
20
BUCK 2
EXTVCC = VOUT2
0
fSW = 2.2MHz EXTVCC = VOUT1
L = 2.2µH
VBAT = 14V
VOUT1 = 5V
90
0
1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01
40
SUPPLY VOLTAGE (V)
IOUT1 (A)
BUCK 2 EFFICIENCY
SWITCHING FREQUENCY
vs. LOAD CURRENT
SWITCHING FREQUENCY
vs. RFOSC (MAX16930)
fSW = 2.2MHz EXTVCC = VOUT2
L = 2.2µH
VBAT = 14V
VOUT2 = 3.3V
SKIP MODE
EXTVCC =
GND
EXTVCC =
VOUT2
20
EXTVCC =
GND
PWM MODE
10
0
1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01
IOUT1 (A)
www.maximintegrated.com
2.30
2.28
BUCK 2
2.26
2.24
2.22
BUCK 1
2.20
2.18
2.16
2.14
2.12
2.10
0
1
2
3
4
LOAD CURRENT (A)
5
6
MAX16930 toc08
TEMPERATURE (°C)
2.4
SWITCHING FREQUENCY (MHz)
80
50
MAX16930 toc07
90
0
60
10
SWITCHING FREQUENCY (MHz)
100
-60 -40 -20
70
BUCK 1 EFFICIENCY
100
EFFICIENCY (%)
20
80
QUIESCENT CURRENT (µA)
30
MAX16930 toc06
QUIESCENT CURRENT (µA)
40
0
EFFICIENCY (%)
VEN1 = VBAT
VEN2 = 0V
EXTVCC = VOUT1
50
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
MAX16930 toc03
QUIESCENT CURRENT
vs. TEMPERATURE
MAX16930 toc05
2ms/div
60
VBAT
5V/div
2.2
2.0
VBIAS = 5V
1.8
1.6
VBIAS = 3.3V
1.4
1.2
1.0
10
15
20
25
30
RFOSC (kΩ)
Maxim Integrated │ 6
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
2.40
1.0
0.9
SWITCHING FREQUENCY (MHz)
MAX16930 toc09
SWITCHING FREQUENCY (MHz)
1.1
0.8
0.7
VBIAS = 5V
0.6
0.5
0.4
0.3
0.2
2.35
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX16930 toc10
SWITCHING FREQUENCY
vs. RFOSC (MAX16931)
RFOSC = 13.7kΩ
2.30
2.25
2.20
2.15
2.10
2.05
VBIAS = 3.3V
2.00
30 40 50 60 70 80 90 100 110 120 130 140 150 160 170
-60 -40 -20 0
RFOSC (kΩ)
LOAD TRANSIENT RESPONSE
DIPS AND DROPS
EXTERNAL FSYNC TRANSITION
MAX16930 toc12
MAX16930 toc11
20 40 60 80 100 120 140
TEMPERATURE (ºC)
MAX16930 toc13
VBAT
10V/div
VLX1
10V/div
VOUT1
100mV/div
VLX2
10V/div
IOUT1
1A/div
400µs/div
LOAD DUMP
SLOW VIN RAMP
VOUT2
1V/div
SHORT-CIRCUIT RESPONSE
MAX16930 toc15
MAX16930 toc16
IOUT1
2A/div
VOUT1
2V/div
VPGOOD1
5V/div
VOUT2
2V/div
VPGOOD2
5V/div
VPGOOD2
5V/div
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40ms/div
VBAT
5V/div
VBAT
10V/div
LOAD DUMP, PWM
100ms/div
VOUT1
5V/div
VFSYNC
2V/div
400ns/div
MAX16930 toc14
VPGOOD1
5V/div
10s/div
200µs/div
VOUT1
1V/div
VPGOOD1
2V/div
Maxim Integrated │ 7
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX16930 toc17
BUCK 1 LOAD REGULATION
4.998
VFSYNC = VBIAS
4.997
VOUT1
1V/div
VPGOOD1
2V/div
MAX16930 toc18
OUTPUT OVERVOLTAGE RESPONSE
4.996
VOUT_ (V)
4.995
4.994
4.993
4.992
4.991
4.990
4.989
1s/div
0
1
2
3
4
5
6
IOUT_ (A)
3.294
3.293
3.292
99.90
99.85
99.80
3.290
99.75
0
1
2
3
4
99.70
6
5
1.005
1.000
-60 -40 -20 0
20 40 60 80 100 120 140
0.990
0
10
15
20
25
30
35
40
VSUP (V)
MINIMUM ON-TIME (BUCK 1)
FB2 LINE REGULATION
MAX16930 toc22
MAX16930 toc23
VOUT1 = 1.8V
IOUT1 = 300mA
VBAT
5V/div
1.000
0.995
0.990
5
TEMPERATURE (ºC)
1.005
VOUT_ (V)
VOUT1 =1.8V
0.995
IOUT_ (A)
1.010
VOUT2
VOUT1
99.95
3.291
3.289
EXTVCC = VGND
VFSYNC = VBIAS
IOUT_ =0A
FB1 LINE REGULATION
1.010
MAX16930 toc21
100.00
VOUT_ (%nominal)
VOUT_ (V)
3.295
100.05
VOUT_ vs. TEMPERATURE
VOUT_ (V)
MAX16930 toc19
VFSYNC = VBIAS
3.296
100.10
MAX16930 toc20
BUCK 2 LOAD REGULATION
3.297
VOUT1
1V/div
0
5
10
15
20
25
30
35
40
200ns/div
VSUP (V)
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Maxim Integrated │ 8
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MINIMUM ON-TIME (BUCK 2)
COLD CRANK (PREBOOST ON)
MAX16930 toc24
BOOST ENABLE
MAX16930 toc25
MAX16930 toc26
IOUT2 = 300mA
VBAT
10V/div
VIN
5V/div
VBSTON
5V/div
VOUT1
5V/div
VPGOOD1
5V/div
VOUT2
5V/div
VPGOOD2
5V/div
VBAT
5V/div
VOUT1
1V/div
VIN
5V/div
VSNS
1V/div
VBSTON
5V/div
400ms/div
LX WAVEFORMS
MAX16930 toc27
2s/div
IOUT1 = IOUT2 = 1A
9.95
VLX1
5V/div
9.90
PREBOOST LOAD REGULATION
MAX16930 toc28
200ns/div
VBAT
5V/div
VBAT = 7V
9.85
VOUT_ (V)
9.80
VLX2
5V/div
9.75
9.70
9.65
9.60
VLXBST
5V/div
9.55
9.50
200ns/div
0
1
2
3
4
5
6
IOUT_ (A)
20
10
0
-10
25
20
15
10
5
0
-5
300 320 340 360 380 400 320 440 460 480 500
FREQUENCY (kHz)
www.maximintegrated.com
-10
SPECTRAL ENERGY DENSITY
vs. FREQUENCY
35
MEASURED ON THE MAX16930BATLS/V+
30
25
MAX16930 toc31
30
MEASURED AT VOUT2 ON
THE MAX16930BATLU/V+
OUTPUT SPECTRUM (dBµV)
30
35
SPECTRAL ENERGY DENSITY
vs. FREQUENCY
MAX16930 toc30
40
40
OUTPUT SPECTRUM (dBµV)
MEASURED ON THE MAX16931BATLS/V+
MAX16930 toc29
OUTPUT SPECTRUM (dBµV)
50
SPECTRAL ENERGY DENSITY
vs. FREQUENCY
20
15
10
5
0
-5
800k
960k
1.0M
FREQUENCY (Hz)
1.1M
1.2M
-10
1.8
2.0
2.2
2.4
2.6
FREQUENCY (MHz)
Maxim Integrated │ 9
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
N.C.
FSYNC
FOSC
COMP2
FB2
CS2
OUT2
PGND2
LX2
TOP VIEW
DL2
Pin Configuration
30 29 28 27 26 25 24 23 22 21
DH2 31
20 PGOOD2
BST2 32
19 PGND3
18 DL3
FSELBST 33
17 TERM
BSTON 34
MAX16930
MAX16931
EN2 35
EN1 36
16 CS3N
15 CS3P
EN3 37
14 INS
N.C. 38
13 FB3
BST1 39
12 PGOOD1
+
4
5
6
7
PGND1
CS1
OUT1
FB1
COMP1
8
9
10
EXTVCC
3
AGND
2
BIAS
1
LX1
11 IN
DL1
DH1 40
TQFN/SIDE-WETTABLE QFND
Pin Description
PIN
NAME
FUNCTION
1
LX1
Inductor Connection for Buck 1. Connect LX1 to the switched side of the inductor. LX1 serves as the
lower supply rail for the DH1 high-side gate drive.
2
DL1
Low-Side Gate Drive Output for Buck 1. DL1 output voltage swings from VPGND1 to VBIAS.
3
PGND1
4
CS1
Positive Current-Sense Input for Buck 1. Connect CS1 to the positive terminal of the current-sense
resistor. See the Current Limiting and Current-Sense Inputs and Current-Sense Measurement
sections.
5
OUT1
Output Sense and Negative Current-Sense Input for Buck 1. When using the internal preset 5V
feedback divider (FB1 = BIAS), the buck uses OUT1 to sense the output voltage. Connect OUT1
to the negative terminal of the current-sense resistor. See the Current Limiting and Current-Sense
Inputs and Current-Sense Measurement sections.
6
FB1
7
COMP1
8
BIAS
9
AGND
10
EXTVCC
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Power Ground for Buck 1
Feedback Input for Buck 1. Connect FB1 to BIAS for the 5V fixed output or to a resistive divider
between OUT1 and GND to adjust the output voltage between 1V and 10V. In adjustable mode,
FB1 regulates to 1V (typ). See the Setting the Output Voltage in Buck Converters section.
Buck 1 Error-Amplifier Output. Connect an RC network to COMP1 to compensate buck 1.
5V Internal Linear Regulator Output. Bypass BIAS to GND with a low-ESR ceramic capacitor of 6.8FF
minimum value. BIAS provides the power to the internal circuitry and external loads. See the Fixed
5V Linear Regulator (BIAS) section.
Signal Ground for IC
3.1V to 5.2V Input to the Switchover Comparator
Maxim Integrated │ 10
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Pin Description (continued)
PIN
11
12
NAME
IN
PGOOD1
FUNCTION
Supply Input. Connect IN to the output of the preboost. Bypass IN with sufficient capacitance to
supply the two out-of-phase buck converters.
Open-Drain Power-Good Output for Buck 1. PGOOD1 is low if OUT1 is more than 15% (typ) below
the normal regulation point. PGOOD1 asserts low during soft-start and in shutdown. PGOOD1
becomes high impedance when OUT1 is in regulation. To obtain a logic signal, pullup PGOOD1
with an external resistor connected to a positive voltage lower than 5.5V. Place a minimum of 100W
(RPGOOD1) in series with PGOOD1. See the Voltage Monitoring (PGOOD_) section for details.
FB3
Preboost Feedback Input. Connect FB3 to the center tap of a resistive-divider between the boost
regulator output and TERM to adjust the output voltage. FB3 regulates to 1.25V (typ). Ensure that the
parallel combination of the resistor-divider network is > 500W. See the Setting the Output Voltage in
Boost Converter section.
14
INS
Input Voltage Sense for Preboost. The voltage at INS is compared to internal comparator reference.
Program the preboost threshold by using resistor-divider from BAT to INS to TERM pin. Ensure
that the parallel combination of the resistor-divider network is > 500W. For the MAX16930ATLV/V+
and MAX16930BATLW/V+, the INS functionality is disabled; however, the INS pin should still be
connected using the resistor-divider between VBAT and the TERM pin.
15
CS3P
Positive Current-Sense Input for Preboost. Connect CS3P to the positive terminal of the currentsense resistor. See the Current Limit in Boost Controller and Shunt Resistor Selection in Boost
Converter sections.
16
CS3N
Negative Current-Sense Input for Preboost. Connect CS3N to the negative terminal of the currentsense resistor. See the Current Limit in Boost Controller and Shunt Resistor Selection in Boost
Converter sections.
17
TERM
Ground Switch. TERM opens when the voltage at EN3 is logic-low. Use TERM to terminate the
preboost feedback and INS resistive divider.
18
DL3
19
PGND3
13
Preboost n-Channel MOSFET Gate-Drive Output
Power Ground for Preboost. All the high-current paths for the preboost should terminate to this
ground.
Open-Drain Power-Good Output for Buck 2. PGOOD2 is low if OUT2 is more than 90% (typ) below
the normal regulation point. PGOOD2 asserts low during soft-start and in shutdown. PGOOD2
becomes high impedance when OUT2 is in regulation. To obtain a logic signal, pullup PGOOD2 with
an external resistor connected to a positive voltage lower than 5.5V.
20
PGOOD2
21, 38
N.C.
22
FSYNC
External Clock Synchronization Input. Synchronization to the controller operating frequency ratio is
1. Keep fSYNC a minimum of 10% greater than the maximum internal switching frequency for stable
operation. See the Switching Frequency/External Synchronization section.
23
FOSC
Frequency Setting Input. Connect a resistor from FOSC to AGND to set the switching frequency of
the DC-DC converters.
24
COMP2
25
FB2
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No Connection
Buck 2 Error Amplifier Output. Connect an RC network to COMP2 to compensate buck 2.
Feedback Input for Buck 2. Connect FB2 to BIAS for the 3.3V fixed output or to a resistive divider
between OUT2 and GND to adjust the output voltage between 1V and 10V. In adjustable mode, FB2
regulates to 1V (typ). See the Setting the Output Voltage in Buck Converters section.
Maxim Integrated │ 11
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Pin Description (continued)
PIN
NAME
FUNCTION
26
OUT2
Output Sense and Negative Current-Sense Input for Buck 2. When using the internal preset 3.3V
feedback-divider (FB2 = BIAS), the buck uses OUT2 to sense the output voltage. Connect OUT2
to the negative terminal of the current-sense resistor. See the Current Limiting and Current-Sense
Inputs and Current-Sense Measurement sections.
27
CS2
Positive Current-Sense Input for Buck 2. Connect CS2 to the positive terminal of the current-sense
resistor. See the Current Limiting and Current-Sense Inputs and Current-Sense Measurement
sections.
28
PGND2
29
DL2
Low-Side Gate Drive Output for Buck 2. DL2 output voltage swings from VPGND2 to VBIAS.
30
LX2
Inductor Connection for Buck 2. Connect LX2 to the switched side of the inductor. LX2 serves as the
lower supply rail for the DH2 high-side gate drive.
31
DH2
High-Side Gate Drive Output for Buck 2. DH2 output voltage swings from VLX2 to VBST2.
32
BST2
Boost Capacitor Connection for High-Side Gate Voltage of Buck 2. Connect a high-voltage diode
between BIAS and BST2. Connect a ceramic capacitor between BST2 and LX2. See the High-Side
Gate-Driver Supply (BST_) section.
33
FSELBST
Frequency Select Pin for the Preboost. When pulled low, the preboost will have the same switching
frequency as buck 1. When pulled high, the preboost will have a switching frequency that is 1/5th
that of buck 1. FSELBST is only active for the MAX16930. FSELBST should be connected to ground
for the MAX16931.
34
BSTON
35
EN2
High-Voltage Tolerant, Active-High Digital Enable Input for Buck 2. Driving EN2 high enables
buck 2.
36
EN1
High-Voltage Tolerant, Active-High Digital Enable Input for Buck 1. Driving EN1 high enables
buck 1.
37
EN3
High-Voltage Tolerant, Active-High Digital Enable Input for Preboost. When EN3 is high, the external
preboost is enabled and begins switching if VINS drops below VINS,OLV and required conditions are
met (see the Preboost section).
39
BST1
Boost Capacitor Connection for High-Side Gate Voltage of Buck 1. Connect a high-voltage diode
between BIAS and BST1. Connect a ceramic capacitor between BST1 and LX1. See the High-Side
Gate-Driver Supply (BST_) section.
40
DH1
High-Side Gate-Drive Output for Buck 1. DH1 output voltage swings from VLX1 to VBST1.
—
EP
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Power Ground for Buck 2
Preboost On-Indicator Output. To obtain a logic signal, pull up BSTON with an external resistor
connected to a positive voltage lower than 5.5V. BSTON goes high to indicate that the preboost
is on.
Exposed Pad. Connect the exposed pad to ground. Connecting the exposed pad to ground does
not remove the requirement for proper ground connections to PGND1, PGND2, PGND3, and AGND.
The exposed pad is attached with epoxy to the substrate of the die, making it an excellent path to
remove heat from the IC.
Maxim Integrated │ 12
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Detailed Description
EXTVCC Switchover
The MAX16930/MAX16931 are automotive-rated tripleoutput switching power supplies. These devices integrate two synchronous step-down controllers and an
asynchronous step-up controller and can provide up to
three independently controlled power rails as follows:
The internal linear regulator can be bypassed by connecting an external supply (3V to 5.2V) or the output
of one of the buck converters to EXTVCC. BIAS internally switches to EXTVCC and the internal linear regulator
turns off. This configuration has several advantages:
• A preboost with adjustable output voltage.
• It reduces the internal power dissipation of the
MAX16930/MAX16931.
• A buck controller with a fixed 5V output voltage or an
adjustable 1V to 10V output voltage.
• A buck controller with a fixed 3.3V output voltage or
an adjustable 1V to 10V output voltage.
• The low-load efficiency improves as the internal supply current gets scaled down proportionally to the
duty cycle.
The buck controllers and the preboost can each provide
up to 10A output current and are independently controllable.
If VEXTVCC drops below VTH,EXTVCC = 3.0V (min), the
internal regulator enables and switches back to BIAS.
Buck 1, buck 2, and the preboost are enabled and
disabled by the EN1, EN2, and EN3 control inputs,
respectively. These are active-high inputs and can be
connected directly to car battery.
Undervoltage Lockout (UVLO)
• EN1 and EN2 enable the respective buck controllers.
Connect EN1 and EN2 directly to VBAT or to powersupply sequencing logic.
The BIAS input undervoltage-lockout (UVLO) circuitry
inhibits switching if the 5V bias supply (BIAS) is below
its 2.9V (typ) UVLO falling threshold. Once the 5V bias
supply (BIAS) rises above its UVLO rising threshold and
EN1 and EN2 enable the buck controllers, the controllers
start switching and the output voltages begin to ramp up
using soft-start.
• EN3 controls the boost controller
Buck Controllers
In standby mode (only buck 2 is active), the total supply
current is reduced to 30µA (typ). When all three controllers are disabled, the total current drawn is further
reduced to 6.8µA.
The MAX16930/MAX16931 provide two buck
controllers with synchronous rectification. The step-down
controllers use a PWM, current-mode control scheme.
External logic-level MOSFETs allow for optimized loadcurrent design. Fixed-frequency operation with optimal
interleaving minimizes input ripple current from the
minimum to the maximum input voltages. Output-current
sensing provides an accurate current limit with a sense
resistor or power dissipation can be reduced using lossless current sensing across the inductor.
Fixed 5V Linear Regulator (BIAS)
The internal circuitry of the MAX16930/MAX16931 requires
a 5V bias supply. An internal 5V linear regulator (BIAS)
generates this bias supply. Bypass BIAS with a 6.8µF or
greater ceramic capacitor to guarantee stability under the
full-load condition.
The internal linear regulator can source up to 100mA
(150mA under EXTVCC switchover, see the EXTVCC
Switchover section). Use the following equation to estimate the internal current requirements for the MAX16930/
MAX16931:
IBIAS = ICC + fSW(QG_DL3 + QG_DH1 + QG_DL1 +
QG_DH2 + QG_DL2) = 10mA to 50mA (typ)
where ICC is the internal supply current, 5mA (typ), fSW
is the switching frequency, and QG_ is the MOSFET’s
total gate charge (specification limits at VGS = 5V). To
minimize the internal power dissipation, bypass BIAS to
an external 5V rail.
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Soft-Start
Once a buck converter is enabled by driving the corresponding EN_ high, the soft-start circuitry gradually
ramps up the reference voltage during soft-start time
(tSSTART = 6ms (typ)) to reduce the input surge currents
during startup. Before the device can begin the soft-start,
the following conditions must be met:
1) VBIAS exceeds the 3.4V (max) undervoltage lockout
threshold.
2) VEN_ is logic-high.
Maxim Integrated │ 13
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Switching Frequency/External Synchronization
Maximum Duty-Cycle Operation
The MAX16930 provides an internal oscillator adjustable from 1MHz to 2.2MHz. The MAX16931 provides
an internal oscillator adjustable from 200kHz to 1MHz.
High-frequency operation optimizes the application for
the smallest component size, trading off efficiency to
higher switching losses. Low-frequency operation offers
the best overall efficiency at the expense of component
size and board space. To set the switching frequency,
connect a resistor RFOSC from FOSC to AGND. See
TOCs 8 and 9 in the Typical Operating Characteristics
section to determine the relationship between switching
frequency and RFOSC.
The devices have a maximum duty cycle of 95%. The
internal logic of the IC looks for approximately 8 to 10
consecutive high-side FET ON pulses and decides to
turn ON the low-side FET for 150ns (typ) every 12μs. The
input voltage at which the devices enter dropout changes
depending on the input voltage, output voltage, switching
frequency, load current, and the efficiency of the design.
The input voltage at which the devices enter dropout can
be approximated as:
Buck 1 and the boost converter are synchronized with
the internal clock-signal rising edge, while buck 2 is
synchronized with the clock-signal falling edge. The
preboost enables the low-side switch (DL3) with the
rising edge of the cycle while buck 1 turns on its highside n-channel MOSFET (DH1).
The devices can be synchronized to an external clock by
connecting the external clock signal to FSYNC. A rising
edge on FSYNC resets the internal clock. Keep the FSYNC
frequency between 110% and 125% of the internal
frequency. The FSYNC signal should have a 50% duty cycle.
Light-Load Efficiency Skip Mode (VFSYNC = 0V)
Drive FSYNC low to enable skip mode. In skip mode, the
devices stop switching until the FB voltage drops below
the reference voltage. Once the FB voltage has dropped
below the reference voltage, the devices begin switching
until the inductor current reaches 30% (skip threshold)
of the maximum current defined by the inductor DCR or
output shunt resistor.
Forced-PWM Mode (VFSYNC)
Driving FSYNC high prevents the devices from entering skip mode by disabling the zero-crossing detection
of the inductor current. This forces the low-side gatedriver waveform to constantly be the complement of
the high-side gate-drive waveform, so the inductor current reverses at light loads and discharges the output
capacitor. The benefit of forced PWM mode is to keep the
switching frequency constant under all load conditions.
However, forced-frequency operation diverts a considerable amount of the output current to PGND, reducing the
efficiency under light-load conditions.
Forced-PWM mode is useful for improving load-transient
response and eliminating unknown frequency harmonics
that can interfere with AM radio bands.
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VOUT = [VOUT + (IOUT x RON_H)]/0.95
Note: The above equation does not take into account the
efficiency and switching frequency, but is a good firstorder approximation. Use the RON_H max number from
the data sheet of the high-side MOSFET used.
Spread Spectrum
The MAX16930AGLS/MAX16930BAGLU/MAX16931BAGLS
feature enhanced EMI performance. They perform Q6%
dithering of the switching frequency to reduce peak
emission noise at the clock frequency and its harmonics, making it easier to meet stringent emission limits.
When using an external clock source (i.e., driving the
FSYNC input with an external clock), spread spectrum
is disabled.
Buck 2 Switching Frequency
For the MAX16930ATLT and MAX16930BATLU, the switching frequency of buck 2 is set to 1/2 of fSW (buck 1 switching
frequency). When using these devices, the external components of buck 2 should be sized to account for the reduced
switching frequencies (see the Design Procedure section).
MOSFET Gate Drivers (DH_ and DL_)
The DH_ high-side n-channel MOSFET drivers are powered from capacitors at BST_ while the low-side drivers
(DL_) are powered by the 5V linear regulator (BIAS). On
each channel, a shoot-through protection circuit monitors
the gate-to-source voltage of the external MOSFETs to
prevent a MOSFET from turning on until the complementary switch is fully off. There must be a low-resistance,
low-inductance path from the DL_ and DH_ drivers to the
MOSFET gates for the protection circuits to work properly.
Follow the instructions listed to provide the necessary lowresistance and low-inductance path:
• Use very short, wide traces (50 mils to 100 mils wide
if the MOSFET is 1in from the driver).
It may be necessary to decrease the slew rate for the
gate drivers to reduce switching noise or to compensate
for low-gate charge capacitors. For the low-side drivers,
Maxim Integrated │ 14
MAX16930/MAX16931
use gate capacitors in the range of 1nF to 5nF from DL_
to GND. For the high-side drivers, connect a small 5I to
10I resistor between BST_ and the bootstrap capacitor.
Note: Gate drivers must be protected during shutdown,
at the absence of the supply voltage (VBIAS = 0V) when
the gate is pulled high either capacitively or by the leakage path on the PCB. Therefore, external gate pulldown
resistors are needed, especially at DL3 to prevent making a direct path from VBAT to GND.
High-Side Gate-Driver Supply (BST_)
The high-side MOSFET is turned on by closing an internal switch between BST_ and DH_ and transferring the
bootstrap capacitor’s (at BST_) charge to the gate of
the high-side MOSFET. This charge refreshes when the
high-side MOSFET turns off and the LX_ voltage drops
down to ground potential, taking the negative terminal
of the capacitor to the same potential. At this time the
bootstrap diode recharges the positive terminal of the
bootstrap capacitor.
The selected n-channel high-side MOSFET determines the
appropriate boost capacitance values (CBST_ in the Typical
Operating Circuit) according to the following equation:
C BST_ =
QG
∆VBST_
where QG is the total gate charge of the high-side
MOSFET and DVBST_ is the voltage variation allowed on
the high-side MOSFET driver after turn-on. Choose
DVBST_ such that the available gate-drive voltage is not
significantly degraded (e.g., DVBST_ = 100mV to 300mV)
when determining CBST_. The boost capacitor should be
a low-ESR ceramic capacitor. A minimum value of 100nF
works in most cases.
Current Limiting and Current-Sense Inputs
(OUT_ and CS_)
The current-limit circuit uses differential current-sense
inputs (OUT_ and CS_) to limit the peak inductor current.
If the magnitude of the current-sense signal exceeds the
current-limit threshold (VLIMIT1,2 = 80mV (typ)), the PWM
controller turns off the high-side MOSFET. The actual
maximum load current is less than the peak currentlimit threshold by an amount equal to half of the inductor
ripple current. Therefore, the maximum load capability is
a function of the current-sense resistance, inductor value,
switching frequency, and duty cycle (VOUT_/VIN).
For the most accurate current sensing, use a current-sense
shunt resistor (RSH) between the inductor and the output
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2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
capacitor. Connect CS_ to the inductor side of RSH and
OUT_ to the capacitor side. Dimension RSH such that
the maximum inductor current (IL,MAX = ILOAD,MAX+1/2
IRIPPLE,PP) induces a voltage of VLIMIT1,2 across RSH
including all tolerances. For higher efficiency, the current
can also be measured directly across the inductor. This
method could cause up to 30% error over the entire temperature range and requires a filter network in the currentsense circuit. See the Current-Sense Measurement section.
Voltage Monitoring (PGOOD_)
The MAX16930/MAX16931 include several power
monitoring signals to facilitate power-supply sequencing
and supervision. PGOOD_ can be used to enable circuits
that are supplied by the corresponding voltage rail, or to
turn on subsequent supplies.
Each PGOOD_ goes high (high impedance) when the
corresponding regulator output voltage is in regulation.
Each PGOOD_ goes low when the corresponding regulator output voltage drops below 15% (typ) or rises above
15% (typ) of its nominal regulated voltage. Connect a
10kI (typ) pullup resistor from PGOOD_ to the relevant
logic rail to level-shift the signal. PGOOD_ asserts low
during soft-start, soft-discharge, and when either buck
converter is disabled (either EN1 or EN2 is low). To
ensure latchup immunity on the PGOOD1 pin in compliance with the AEC-Q100 guidelines, a minimum resistance of 100I should be placed between the PGOOD1
pin and any other external components.
Supply Monitoring (INS)
The supply voltage in automotive systems can vary significantly and indicate potentially dangerous situations
for the application. Undervoltage transients can indicate
impending loss of power (for example during engine-start
with a weak battery), while overvoltage conditions can
quickly exceed the thermal budget of the application.
The devices include a dedicated battery voltage sensor
at INS to quickly detect overvoltage and undervoltage for
the boost converter.
SIGNAL
VBAT(MIN)
(V)
VBAT(TYP)
(V)
VBAT(MAX)
(V)
VINS,OFF
10.38
10.81
11.25
VINS,ON,SW
9.515
9.95
10.38
VINS,UV
Rising
2.81
3.0275
3.24
VINS,UV
Falling
2.38
2.6
2.81
Maxim Integrated │ 15
MAX16930/MAX16931
Connect INS to the center tap of a resistive divider from
the input voltage (battery) to TERM to set the threshold
voltage for VINS,OFF, VINS,ON,SW, and VINS,UV. For
example, with a 153kI ±1% resistor between INS and
VBAT and a 20kI ±1% resistor between INS and TERM,
the following typical automotive VBAT levels can be
sensed, allowing for proper turn-on/turn-off of the preboost. If this setting is not sufficient, optimize the divider
for the most critical level. For the MAX16930ATLV/V+
and MAX16930BATLW/V+, the INS pin functionality is
disabled; however, the INS pin should still be connected
using the resistor-divider between VBAT and the TERM
pin, as explained above.
Preboost
The MAX16930/MAX16931 include an asynchronous
current-mode preboost with adjustable output. This preboost can be used independently, but is ideally suited
for applications that need to stay fully functional during
input voltage dropouts typical for automotive cold-crank
or start-stop.
The preboost is turned on by bringing EN3 high.
EN3 can be used for power-supply sequencing and
implementing a boost timeout to prevent overheating the
components used for the boost converter.
While the boost circuit is essential to maintain functionality
during undervoltage events, it reduces system efficiency.
During normal operation, the boost diode dissipates
power and the resistive dividers at INS and FB3 sink
significant amounts of quiescent current. To ensure
latchup immunity on the INS and FB3 pins in compliance with the AEC-Q100 guidelines, ensure that the
parallel combination of this resistor-divider network used
on these pins is > 500ω.
Increasing the Efficiency of the Boost Circuit
(TERM)
The MAX16930/MAX16931 provide a feature to improve
the efficiency of the boost circuit when it is not active:
• TERM provides a switch to GND for the INS and FB3
voltage-dividers. This switch opens during standby
mode and shutdown mode to reduce the quiescent
current by 240µA, assuming that resistors used in the
voltage-divider network are in the range of 100kI.
Preboost n-Channel MOSFET Driver (DL3)
DL3 drives the gate of an external n-channel MOSFET.
The driver is powered by the 5V (typ) internal regulator
(BIAS) or the external bypass supply (EVTVCC). DL3
asserts low during standby mode.
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2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Switching Frequency in Boost Controller
The preboost switching frequency (fBOOST) is derived
from the buck controllers switching frequency (fSW) by
setting FOSC. See the Electrical Characteristics table.
On the MAX16930, fBOOST can be set equal to fSW by
connecting FBSTSEL to ground or to 1/5fSW by connecting FBSTSEL to BIAS. The gate driver of the preboost
turns on simultaneously with the high-side driver of buck
1. FSELBST should be connected to ground on the
MAX16931.
Current Limit in Boost Controller
A current-sense resistor (RCS), connected CS3P and
CS3N, sets the current limit of the boost converter. The
CS input has a voltage trip level (VCS) of 120mV (typ).
The low 120mV current-limit threshold reduces the power
dissipation in the current-sense resistor. Use a currentsense filter to reduce capacitive coupling during turn
on. See the Shunt Resistor Selection in Boost Converter
section.
Thermal-Overload, Overcurrent, and
Overvoltage and Undervoltage Behavior
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation
in the devices. When the junction temperature exceeds
+170NC, an internal thermal sensor shuts down the
devices, allowing them to cool. The thermal sensor turns
on the devices again after the junction temperature cools
by 20NC.
Overcurrent Protection
If the inductor current on the MAX16930 and MAX16931
exceed the maximum current limit programmed at
CS_ and OUT_, the respective driver turns off. In an
overcurrent mode, this results in shorter and shorter highside pulses.
A hard short results in a minimum on-time pulse every
clock cycle.
Choose the components so they can withstand the shortcircuit current if required.
Overvoltage Protection
The devices limit the output voltage of the buck converters by turning off the high-side gate driver at approximately 115% of the regulated output voltage. The output
voltage needs to come back in regulation before the
high-side gate driver starts switching again.
Maxim Integrated │ 16
MAX16930/MAX16931
Design Procedure
Buck Converter Design Procedure
Effective Input Voltage Range in Buck Converters
Although the MAX16930/MAX16931 can operate from
input supplies up to 36V (42V transients) and regulate
down to 1V, the minimum voltage conversion ratio (VOUT/
VIN) might be limited by the minimum controllable on-time.
For proper fixed-frequency PWM operation and optimal
efficiency, buck 1 and buck 2 should operate in continuous conduction during normal operating conditions. For
continuous conduction, set the voltage conversion ratio
as follows:
VOUT
VIN
> t ON(MIN) × fSW
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
DC output accuracy specifications in the Electrical
Characteristics table refer to the error comparator’s
threshold, VFB_ = 1V (typ). When the inductor conducts
continuously, the devices regulate the peak of the output
ripple, so the actual DC output voltage is lower than the
slope-compensated trip level by 50% of the output ripple
voltage.
In discontinuous conduction mode (skip or STDBY active
and IOUT < ILOAD(SKIP)), the devices regulate the valley of
the output ripple, so the output voltage has a DC regulation
level higher than the error-comparator threshold.
Inductor Selection in Buck Converters
Three key inductor parameters must be specified for
operation with the MAX16930/MAX16931: inductance
value (L), inductor saturation current (ISAT), and DC
resistance (RDCR). To determine the optimum inductance, knowing the typical duty cycle (D) is important.
where tON(MIN) is 50ns (typ) and fSW is the switching
frequency in Hz. If the desired voltage conversion does
not meet the above condition, pulse skipping occurs to
VOUT
VOUT
decrease the effective duty cycle. Decrease the switching=
D =
OR D
V
V
I
(R
−
IN
IN OUT DS(ON) + R DCR )
frequency if constant switching frequency is required. The
same is true for the maximum voltage conversion ratio.
if the RDCR of the inductor and RDS(ON) of the MOSFET
The maximum voltage conversion ratio is limited by the
are available with VIN = (VBAT - VDIODE). All values
maximum duty cycle (95%).
should be typical to optimize the design for normal
operation.
VOUT
< 0.95
VIN − VDROP
Inductance
The exact inductor value is not critical and can be
where VDROP = IOUT (RON,HS + RDCR) is the sum of the
adjusted in order to make trade-offs among size, cost,
parasitic voltage drops in the high-side path and fSW is
efficiency, and transient response requirements.
the programmed switching frequency. During low drop
• Lower inductor values increase LIR, which minimizes
operation, the devices reduce fSW to 25% (max) of the
size and cost and improves transient response at the
programmed frequency. In practice, the above condition
cost of reduced efficiency due to higher peak currents.
should be met with adequate margin for good load-transient response.
• Higher inductance values decrease LIR, which
increases efficiency by reducing the RMS current at
Setting the Output Voltage in Buck Converters
the cost of requiring larger output capacitors to meet
Connect FB1 and FB2 to BIAS to enable the fixed buck
load-transient specifications.
controller output voltages (5V and 3.3V) set by a preset
The
ratio of the inductor peak-to-peak AC current to DC
internal resistive voltage-divider connected between the
average
current (LIR) must be selected first. A good inifeedback (FB_) and AGND. To externally adjust the output
tial value is a 30% peak-to-peak ripple current to averagevoltage between 1V and 10V, connect a resistive divider
current ratio (LIR = 0.3). The switching frequency, input
from the output (OUT_) to FB_ to AGND (see the Typical
voltage, output voltage, and selected LIR then determine
Operating Circuit. Calculate RFB_1 and RFB_2 with the
the inductor value as follows:
following equation:
VOUT_
(VIN − VOUT )x D
R FB_1 R FB_2
=
− 1
L[µH] =
VFB_
fSW [MHz]x IOUT x LIR
where VFB_ = 1V (typ) (see the Electrical Characteristics
table).
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where VIN, VOUT, and IOUT are typical values (so that
efficiency is optimum for typical conditions).
Maxim Integrated │ 17
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Peak Inductor Current
Current-Sense Measurement
Inductors are rated for maximum saturation current. The
maximum inductor current equals the maximum load
current in addition to half of the peak-to-peak ripple
current:
=
IPEAK ILOAD(MAX) +
∆IINDUCTOR
2
For the selected inductance value, the actual peak-to-peak
inductor ripple current (DIINDUCTOR) is calculated as:
VOUT (VIN − VOUT )
∆IINDUCTOR =
VIN x fSW x L
For the best current-sense accuracy and overcurrent protection, use a ±1% tolerance current-sense
resistor between the inductor and output as shown in
Figure 1A. This configuration constantly monitors the
inductor current, allowing accurate current-limit protection. Use low-inductance current-sense resistors
for accurate measurement.
Alternatively, high-power applications that do not require
highly accurate current-limit protection can reduce the
overall power dissipation by connecting a series RC
circuit across the inductor (Figure 1B) with an equivalent
time constant:
R2
R CSHL =
R DCR
R1 + R2
where DIINDUCTOR is in mA, L is in µH, and fSW is in kHz.
Once the peak current and the inductance are known, the
inductor can be selected. The saturation current should
be larger than IPEAK or at least in a range where the
inductance does not degrade significantly. The MOSFETs
are required to handle the same range of current without
dissipating too much power.
MOSFET Selection in Buck Converters
Each step-down controller drives two external logic-level
n-channel MOSFETs as the circuit switch elements. The
key selection parameters to choose these MOSFETs
include the items in the following sections.
Threshold Voltage
All four n-channel MOSFETs must be a logic-level type
with guaranteed on-resistance specifications at VGS =
4.5V. If the internal regulator is bypassed (for example:
VEXTVCC = 3.3V), then the n-channel MOSFETs should
be chosen to have guaranteed on-resistance at that
gate-to-source voltage.
Maximum Drain-to-Source Voltage (VDS(MAX))
All MOSFETs must be chosen with an appropriate VDS
rating to handle all VIN voltage conditions.
Current Capability
The n-channel MOSFETs must deliver the average current
to the load and the peak current during switching. Choose
MOSFETs with the appropriate average current at VGS =
4.5V or VGS = VEXTVCC when the internal linear regulator
is bypassed. For load currents below approximately 3A,
dual MOSFETs in a single package can be an economical
solution. To reduce switching noise for smaller MOSFETs,
use a series resistor in the BST_ path and additional gate
capacitance. Contact the factory for guidance using gate
resistors.
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and:
R DCR
=
L
C EQ
1
1
R1 + R2
where RCSHL is the required current-sense resistor and
RDCR is the inductor’s series DC resistor. Use the inductance and RDCR values provided by the inductor
manufacturer.
Carefully observe the PCB layout guidelines to ensure
the noise and DC errors do no corrupt the differential
current-sense signals seen by CS_ and OUT_. Place
the sense resistor close to the devices with short, direct
traces, making a Kelvin-sense connection to the currentsense resistor.
Input Capacitor in Buck Converters
The discontinuous input current of the buck converter
causes large input ripple currents and therefore the
input capacitor must be carefully chosen to withstand
the input ripple current and keep the input voltage
ripple within design requirements. The 180° ripple phase
operation increases the frequency of the input capacitor
ripple current to twice the individual converter switching
frequency. When using ripple phasing, the worst-case
input capacitor ripple current is when the converter with
the highest output current is on.
The input voltage ripple is composed of DVQ (caused by
the capacitor discharge) and DVESR (caused by the ESR
of the input capacitor). The total voltage ripple is the sum
of DVQ and DVESR that peaks at the end of an on-cycle.
Maxim Integrated │ 18
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
Calculate the input capacitance and ESR required for a
specific ripple using the following equation:
∆VESR
ESR[ W ] =
∆IP − P
ILOAD(MAX) +
2
V
ILOAD(MAX) x OUT
VIN
CIN [µF] =
(∆VQ x fSW )
where:
(VIN − VOUT ) x VOUT
∆IP −P =
VIN x fSW x L
ILOAD(MAX) is the maximum output current in A, DIP-P is
the peak-to-peak inductor current in A, fSW is the switching frequency in MHz, and L is the inductor value in µH.
The internal 5V linear regulator (BIAS) includes an output
UVLO with hysteresis to avoid unintentional chattering
during turn-on. Use additional bulk capacitance if the
input source impedance is high. At lower input voltage,
additional input capacitance helps avoid possible undershoot below the undervoltage lockout threshold during
transient loading.
INPUT (VIN)
CIN
MAX16930/
MAX16931
DH_
NH
RSENSE
L
LX_
DL_
COUT
NL
GND
CS_
OUT_
A) OUTPUT SERIES RESISTOR SENSING
INPUT (VIN)
CIN
MAX16930/
MAX16931
DH_
NH
INDUCTOR
L
DCR
R1
R2
LX_
DL_
NL
GND
CS_
OUT_
CEQ
COUT
RCSHL =
RDCR =
( )
[ ]
R2
R
R1 + R2 DCR
L
1 + 1
CEQ R1 R2
B) LOSSLESS INDUCTOR SENSING
Figure 1. Current-Sense Configurartions
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Maxim Integrated │ 19
MAX16930/MAX16931
Output Capacitor in Buck Converters
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. The capacitor
is usually selected by ESR and the 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 VSAG and VSOAR 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 (see the Transient Considerations
section). However, low-capacity filter capacitors typically
have high-ESR zeros that can affect the overall stability.
The total voltage sag (VSAG) can be calculated as follows:
VSAG =
L( ∆ILOAD(MAX) ) 2
2C OUT ((VIN × D MAX ) − VOUT )
+
∆ILOAD(MAX) (t − ∆t)
C OUT
The amount of overshoot (VSOAR) during a full-load to
no-load transient due to stored inductor energy can be
calculated as:
( ∆ILOAD(MAX) ) 2 L
VSOAR ≈
2C OUT VOUT
ESR Considerations
The output filter capacitor must have low enough
equivalent series resistance (ESR) to meet output
ripple and load-transient requirements, yet have high
enough ESR to satisfy stability requirements. When using
high-capacitance, low-ESR capacitors, the filter
capacitor’s ESR dominates the output-voltage ripple. So
the output capacitor’s size depends on the maximum ESR
required to meet the output-voltage ripple (VRIPPLE(P-P))
specifications:
VRIPPLE(P −P) = ESR x ILOAD(MAX) x LIR
In standby mode, the inductor current becomes discontinuous, with peak currents set by the idle-mode currentsense threshold (VCS,SKIP = 26mV (typ)).
Transient Considerations
The output capacitor must be large enough to absorb
the inductor energy while transitioning from no-load to
full-load condition without tripping the overvoltage fault
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2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
protection. The total output-voltage sag is the sum of
the voltage sag while the inductor is ramping up and the
voltage sag before the next pulse can occur. Therefore:
(
)
2
L ∆ILOAD(MAX)
C OUT =
2VSAG (VIN x D MAX − VOUT )
+
∆ILOAD(MAX) (t − ∆t)
VSAG
where DMAX is the maximum duty factor (approximately
95%), L is the inductor value in µH, COUT is the output
capacitor value in µF, t is the switching period (1/fSW) in
µs, and Dt equals (VOUT/VIN) x t.
The MAX16930/MAX16931 use a current-mode control
scheme that regulates the output voltage by forcing
the required current through the external inductor, so
the controller uses the voltage drop across the DC
resistance of the inductor or the alternate series currentsense resistor to measure the inductor current. Currentmode control eliminates the double pole in the feedback
loop caused by the inductor and output capacitor resulting in a smaller phase shift and requiring less elaborate
error-amplifier compensation than voltage-mode control.
A single series resistor (RC) and capacitor (CC) is all
that is required to have a stable, high-bandwidth loop in
applications where ceramic capacitors are used for output filtering (see Figure 2). For other types of capacitors,
due to the higher capacitance and ESR, the frequency
of the zero created by the capacitance and ESR is
lower than the desired closed-loop crossover frequency.
To stabilize a nonceramic output capacitor loop, add
another compensation capacitor (CF) from COMP to
AGND to cancel this ESR zero.
The basic regulator loop is modeled as a power
modulator, output feedback divider, and an error
amplifier as shown in Figure 2. The power modulator has
a DC gain set by gmc x RLOAD, with a pole and zero pair
set by RLOAD, the output capacitor (COUT), and its ESR.
The loop response is set by the following equations:
GAINMOD(dc)
= g mc × R LOAD
where RLOAD = VOUT/ILOUT(MAX) in I and gmc =
1/(AV_CS x RDC) in S. AV_CS is the voltage gain of the
current-sense amplifier and is typically 11V/V. RDC is the
DC resistance of the inductor or the current-sense
resistor in I.
Maxim Integrated │ 20
MAX16930/MAX16931
2MHz, 36V, Dual Buck with Preboost and
20µA Quiescent Current
A dominant pole (fdpEA) is set by the compensation
capacitor (CC) and the amplifier output resistance
(ROUT,EA). A zero (fZEA) is set by the compensation
resistor (RC) and the compensation capacitor (CC). There
is an optional pole (fPEA) set by CF and RC to cancel the
output capacitor ESR zero if it occurs near the crossover
frequency (fC), where the loop gain equals 1 (0dB)). Thus:
gmc = 1/(AVCS x RDC)
CS_
CURRENT-MODE
POWER
MODULATION
OUT_
R1
RESR
COUT
gmea = 1200µS
fdpEA =
FB_
COMP_
ERROR
AMP
R2
VREF
30MI
RC
CF
1
2π × C C × (R OUT,EA + R C )
fzEA =
1
2π × C C × R C
fpEA =
1
2π × C F × R C
CC
Figure 2. Compensation Network
In a current-mode step-down converter, the output capacitor and the load resistance introduce a pole at the following frequency:
fpMOD =
1
2π × C OUT × R LOAD
The unity gain frequency of the power stage is set by
COUT and gmc:
g mc
fUGAINpMOD =
2π × C OUT
The output capacitor and its ESR also introduce a zero at:
fzMOD =
1
2π × ESR × C OUT
When COUT is composed of “n” identical capacitors in
parallel, the resulting COUT = n x COUT(EACH), and ESR =
ESR(EACH) /n. Note that the capacitor zero for a parallel
combination of alike capacitors is the same as for an individual capacitor.
The feedback voltage-divider has a gain of GAINFB =
VFB /VOUT, where VFB is 1V (typ).
The transconductance error amplifier has a DC gain of
GAINEA(DC) = gm,EA x ROUT,EA, where gm,EA is the error
amplifier transconductance, which is 1200µS (typ), and
ROUT,EA is the output resistance of the error amplifier,
which is 30MI (typ) (see the Electrical Characteristics
table.)
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The loop-gain crossover frequency (fC) should be set
below 1/5th of the switching frequency and much higher
than the power-modulator pole (fpMOD). Select a value
for fC in the range:
f
fpMOD
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