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MAX20098
Versatile Automotive 36V 2.2MHz Buck
Controller with 3.5μA IQ
General Description
Benefits and Features
The MAX20098 is an automotive 2.2MHz synchronous
step-down controller IC with 3.5µA IQ. This IC operates
with an input-voltage supply from 3.5V to 42V and can operate in dropout condition by running at 99% (typ) duty cycle. It is intended for applications with mid- to high- power requirements that operate at a wide input voltage range
such as during automotive cold-crank or engine stop-start
conditions.
● Meets Stringent Automotive OEM Module Power
Consumption and Performance Specifications
• 3.5µA Quiescent Current in Skip Mode at VOUT =
3.3V
• Fixed 5.0V/3.3V or Adjustable 1V to 10V Output
• ±1.1% Output-Voltage Accuracy for 5V Fixed
Setting
The step-down controller operates at up to 2.2MHz frequency to allow small external components, reduced output ripple, and to guarantee no AM band interference.
The switching frequency is resistor adjustable (220kHz
to 2.2MHz). FSYNC input programmability enables three
frequency modes for optimized performance: forced fixedfrequency operation, skip mode with ultra-low quiescent
current, and synchronization to an external clock. The IC
also provides a SYNC output to enable two controllers to
operate in parallel. The IC has a factory-programmable
spread-spectrum option for frequency modulation to minimize EMI interference.
The PGOOD output indicates when the voltage is within
regulation range. Protection features include cycle-by- cycle current limit and thermal shutdown. The MAX20098 is
specified for operation over the -40°C to +125°C auto- motive temperature range.
Applications
● Infotainment Systems
● USB Hub
● General-Purpose Point-of-Load (POL)
● Enables Crank-Ready Designs
• Wide Input Supply Range from 3.5V to 42V
● EMI Reduction Features Reduce Interference with
Sensitive Radio Bands without Sacrificing Wide Input
Voltage Range
• 50ns (typ) Minimum On-Time Allows
• Skip-Free Operation for 3.3V Output from Car
Battery at 2.2MHz
• Spread-Spectrum Option
• Frequency-Synchronization Input
• Resistor-Programmable Frequency Between
220kHz and 2.2MHz
● Integration and Thermally Enhanced Packages Save
Board Space and Cost
• 2MHz Step-Down Controller
• Current-Mode Controller with Forced-Continuous
and Skip Modes
• 16-Pin Side-Wettable (SW) TQFN-EP Package
• 20A Reference Design Available
● Protection Features Improve System Reliability
• Supply Undervoltage Lockout
• Overtemperature and Short-Circuit Protection
• Output Overvoltage and Undervoltage Monitoring
• -40°C to +125°C Grade 1 Automotive Temperature
Range
Ordering Information appears at end of data sheet.
19-100089; Rev 15; 12/20
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Simplified Block Diagram
VOUT
L
RCS
VBAT
COUT
CBST
BST
DH
LX
DL
PGND
SUP
CIN
PGOOD
EN
MAX20098
CS
FSYNC/SYNCOUT
FOSC
OUT
RFOSC
AGND
CBIAS
BIAS
FB
COMP
CF
RC
CC
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Maxim Integrated | 2
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
TABLE OF CONTENTS
General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Benefits and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Simplified Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Absolute Maximum Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
SW TQFN-EP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical Operating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Fixed 5V Linear Regulator (BIAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Switchover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Undervoltage Lockout (UVLO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Buck Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Soft-Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Switching Frequency/External Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Light-Load-Efficiency Skip Mode (VFSYNC = 0V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Forced-PWM Mode (VFSYNC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Maximum Duty-Cycle Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Spread Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
MOSFET Gate Drivers (DH and DL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
High-Side Gate-Driver Supply (BST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Current Limiting and Current-Sense Inputs (OUT and CS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Voltage Monitoring (PGOOD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Thermal-Overload, Overcurrent, Overvoltage, and Undervoltage Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Thermal-Overload Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Overvoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Design Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Effective Input Voltage Range in the Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Setting the Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Inductance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Peak Inductor Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
MOSFET Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Threshold Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
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Maxim Integrated | 3
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
TABLE OF CONTENTS (CONTINUED)
Maximum Drain-to-Source Voltage (VDS(MAX)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Current Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Current-Sense Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Input Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Output Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
ESR Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Compensation-Components Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
PCB Layout Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Layout Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Typical Application Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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Maxim Integrated | 4
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
LIST OF FIGURES
Figure 1. Current-Sense Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 2. Compensation Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 3. Layout Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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Maxim Integrated | 5
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Absolute Maximum Ratings
SUP, EN, LX to PGND ........................................... -0.3V to +42V
OUT to AGND......................................................... -0.3V to +12V
CS to OUT ............................................................. -0.3V to +0.3V
BST to LX ................................................................. -0.3V to +6V
FSYNC, FSYNCOUT, FOSC, COMP, FB to AGND.....-0.3V to to
VBIAS + 0.3V
BIAS to AGND .......................................................... -0.3V to +6V
PGOOD to AGND..................................................... -0.3V to +6V
DL to PGND ........................................... -0.3V to to VBIAS + 0.3V
DH to LX ................................................. -0.3V to to VBST + 0.3V
Continuous Power Dissipation (TA = +70°C) ......-40ºC to +125ºC
16 SW TQFN (derate 23.09mW/°C above +70°C) .........1847mW
Operating Temperature Range (Note 5) .............-40ºC to +125ºC
Junction Temperature ....................................................... +150ºC
Storage Temperature Range .............................. -40ºC to +150ºC
Note 1: Switching nodes (LX to PGND, BST to LX, DH to LX, DL to PGND) are self-protected for transient voltages (
(1/FSYNC - 1/FOSC)
1.8
2.6
MHz
FOSC = 400kHz, minimum sync pulse >
(1/ FSYNC - 1/FOSC)
320
480
kHz
Minimum sync-in pulse
100
High threshold
1.4
32
µs
ms
FSYNC INPUT
FSYNC Frequency
Range
FSYNC Switching
Thresholds
ns
Low threshold
0.4
V
INTERNAL LDO BIAS
Internal BIAS Voltage
BIAS UVLO Threshold
VIN > 6V
5
VBIAS rising
VBIAS falling
Switchover Operating
Range
3.1
2.6
V
3.5
2.8
3.2
5.5
V
V
THERMAL OVERLOAD
Thermal Shutdown
Temperature
(Note 4)
165
°C
Thermal Shutdown
Hysteresis
(Note 4)
20
°C
ENABLE LOGIC INPUT
High Threshold
EN
Low Threshold
EN
EN_ Input Bias Current
EN input only, TA = +25ºC
1.8
V
0.01
0.8
V
1
µA
SYNCOUT OUTPUT
SYNCOUT Low Voltage
ISINK = 5mA
0.4
V
SYNCOUT Leakage
Current
TA = +25ºC
1
µA
SPREAD-SPECTRUM INPUT
Spread Spectrum
±6
% of
FOSC
Note 2: 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.
Note 3: During initial startup, VSUP rising must cross 4.5V. The normal operating range is then valid.
Note 4: Guaranteed by design; not production tested
Note 5: The device is designed for continuous operation up to TJ = +125°C for 95,000 hours and TJ = +150°C for 5,000 hours.
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Maxim Integrated | 8
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
QUIESCENT SUPPLY CURRENT
vs. INPUT VOLTAGE
EFFICIENCY vs. LOAD CURRENT
toc01
100
16
90
12
70
FPWM MODE
IQ (μA)
60
50
40
1.4
1.2
10
IIN (μA)
EFFICIENCY(%)
SKIP MODE
8
1
0.8
6
0.6
4
0.4
10
2
0.2
0
0
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
30
20
0.01
0.1
1
10
0
5
10
15
LOAD CURRENT (A)
5
20
toc04
LINE REGULATION
0.20%
toc05
20
LOAD REGULATION
0.70%
toc06
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
0.60%
0.15%
SKIP MODE
0.50%
1.5
1
VIN =14V
VOUT =5V
fsw= 2.2MHz
SKIPMODE
0.5
0.10%
0.00%
0
2
4
6
ILOAD (A)
1.00%
FPWM MODE
6
IOUT= 3A
VOUT= 5V
fsw = 2.2MHz
16
26
0.20%
36
0.10%
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
4
6
STARTUP WAVEFORM
(6A LOAD)
toc09
5V/div
5V/div
VEN
3A/div
3A/div
0.00%
2V/div
FPWM MODE
ILX
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
VOUT
VOUT
5V/div
VPGOOD
20 35 50 65 80 95 110 125
2
toc08
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
VEN
ILX
-0.50%
0
ILOAD(A)
STARTUP WAVEFORM
(NO LOAD)
toc07
-1.00%
-40 -25 -10 5
FPWM MODE
VIN (V)
FREQUENCY vs. TEMPERATURE
0.50%
0.40%
0.30%
SKIP MODE
0.05%
0
VOUT(%)
VOUT(%)
2
IIN (A)
15
VIN (V)
2.5
FREQUENCY (%)
10
VIN (V)
SUPPLYCURR
ENT
vs. LOADCURR
ENT
3
toc03
1.6
VOUT= 5V
fsw = 2.2MHz
SKIP MODE
14
80
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
toc02
2V/div
5V/div
VPGOOD
1ms/div
1ms/div
AMBIENT TEMPERATURE
(°C)
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Maxim Integrated | 9
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
STEADY
-STATE
SITCHING WAVEFORMS
SHUTDOWN WAVEFORM
(6A LOAD)
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
VEN
ILX
VLX
3A/div
VIN
5V/div
VOUT
2V/div
VPGOOD
5V/div
3V/div
ILX
VPGOOD
toc12
VOUT= 5V
fsw = 2.2MHz
FPWM Mode
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
5V/div
VOUT
SLOW VIN RAMP
(NO LOAD)
toc11
toc10
800mA/div
2V/div
5V/div
20µs/div
5s/div
100ns/div
UNDERVOLTAGE PULSE
(NO LOAD)
SHORT
-CIRCUIT RESPONSE
(NO LOAD)
VIN
LOAD-DUMP TEST
(NO LOAD)
toc14
toc13
VIN
5V/div
VOUT
2V/div
toc15
5V/div
VIN = 14V
VOUT= 5V
fsw = 2.2MHz
ILX
3A/div
VPGOOD
2V/div
VOUT
VPGOOD
VOUT= 5V
fsw = 2.2MHz
FPWM Mode
47uF Cin
VIN
10V/div
VOUT
2V/div
VOUT= 5V
fsw = 2.2MHz
FPWM MODE
5V/div
VPGOOD
5V/div
5V/div
10µs/div
toc18
toc17
1.00%
200mV/div
VOUT
SKIP to EXTERNAL CLOCK TRANSITION
OUTPUT VOLTAGE vs. TEMPERATURE
toc16
OUTPUT VOLTAGE (%)
LOAD-STEP TEST
(5VOUT, 2.2MHz, FPWM)
20ms/div
10ms/div
VOUT= 5V
fsw = 2.2MHz
FPWM MODE
0.50%
5V/div
VFSYNC
VLX
10V/div
VOUT
5V
2V/div
0.00%
-0.50%
IOUT
2A/div
100µs/div
-1.00%
-40 -25 -10 5
20 35 50 65 80 95 110 125
1µs/div
AMBIENT TEMPERATURE(
°C)
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Maxim Integrated | 10
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
DL
PGND
BIAS
PGOOD
Pin Configuration
12
11
10
9
TOP VIEW
14
BST
15
EN
16
MAX20098
+
SUP
1
2
3
4
AGND
DH
FSYNC/
SYNCOUT
13
FOSC
LX
8
CS
7
OUT
6
FB
5
COMP
SW TQFN
(3mm x 3mm)
Pin Description
PIN
NAME
1
SUP
2
FOSC
FUNCTION
Supply Input. Bypass SUP with enough capacitors to minimize input ripple.
Frequency-Setting Input. Connect a resistor to FOSC to set the switching frequency of the DC-DC
controller.
External Clock-Synchronization Input. Synchronization to the controller operating-frequency ratio is
1. See the Electrical Characteristics table for frequency range and the Switching Frequency/
External Synchronization section for additional information. Connect FSYNC to AGND to
enable skip mode of operation. Connect to BIAS or an external clock to enable forced-PWM
mode of operation. Factory option allows synchronous output to allow controllers to operate in
parallel.
3
FSYNC/
SYNCOUT
4
AGND
Signal Ground for the IC
5
COMP
Buck Controller Error-Amplifier Output. Connect an RC network to COMP to compensate the buck
controller.
6
FB
7
OUT
Output Sense and Negative Current-Sense Input for Buck Controller. When using the internal
preset feedback-divider (FB = BIAS), the controller uses OUT to sense the output voltage. Connect
OUT to the negative terminal of the current-sense element. See the Current Limiting and CurrentSense Inputs (OUT and CS) and Current-Sense Measurement sections.
8
CS
Positive Current-Sense Input for Buck Controller. Connect CS to the positive terminal of the current
sense element. See the Current Limiting and Current-Sense Inputs (OUT and CS) and CurrentSense Measurement sections.
PGOOD
Open-Drain Power-Good Output for Buck Controller. PGOOD is low if OUT is more than 7% (typ)
below the normal regulation point. PGOOD asserts low during soft-start and in shutdown. PGOOD
becomes high impedance when OUT is in regulation. To obtain a logic signal, pull up PGOOD with
an external resistor connected to a positive voltage lower than 5.5V.
9
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Feedback Input for Buck Controller. Connect FB to BIAS for the fixed output, or to a resistive
divider between OUT and AGND to adjust the output voltage between 1V and 10V. In adjustable
mode, FB regulates to 1V (typ). See the Setting the Output Voltage section.
Maxim Integrated | 11
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Pin Description (continued)
PIN
NAME
FUNCTION
10
BIAS
5V Internal Linear Regulator Output. Bypass BIAS to GND with a low-ESR ceramic capacitor of
2.2μF minimum value. BIAS provides the power to the internal circuitry and external loads. See the
Fixed 5V Linear Regulator (BIAS) section.
11
PGND
12
DL
Low-Side Gate-Driver Output. DL output voltage swings from VPGND to VBIAS.
13
LX
Inductor Connection. Connect LX to the switched side of the inductor. LX serves as the lower
supply rail for the DH high-side gate driver.
14
DH
High-Side Gate-Driver Output. DH output voltage swings from VLX to VBST.
15
BST
Boost Flying-Capacitor Connection. Connect a ceramic capacitor between BST and LX. See the
High-Side Gate-Driver Supply (BST) section. When the switching frequency is greater than 1MHz,
connect a high-voltage Schottky diode between BIAS and BST.
16
EN
High-Voltage Tolerant, Active-High Digital-Enable Input for the Controller
EP
-
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Power Ground for the Controller
Exposed Pad. Connect the exposed pad to ground. Connecting the exposed pad to ground does
not remove the requirement for proper ground connections to PGND 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
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Block Diagram
PGOOD HIGH LEVEL
COMP
PGOOD
PGOOD LOW LEVEL
SUP
COMP
FB
FEEDBACKSELECT LOGIC
–
EAMP
BIAS
+
SOFT-START
OUT
EN
VREF = 1V
BST
–
80mV (typ)
+
CSA
PWM
PWM
+
–
CS
CLK
–
DH
STEP-DOWN DC-DC1
GATE-DRIVE
LOGIC
LX
CL
SLOPE COMP
+
EN
CURRENT-LIMIT
THRESHOLD
FOSC
ZEROCROSSING
COMP
LX
ZX
DL
LX
PGND
VSUP
CLK
OSCILLATOR
SPREAD SPECTRUM
ON or OFF
BIAS
EXTERNAL
CLOCK INPUT
INTERNAL LINEAR
REGULATOR
BIAS
FSYNC/SYNCOUT
FSYNC-SELECT
LOGIC
CONNECTED HIGH (PWM MODE)
CONNECTED LOW (SKIP MODE)
OUT
SWITCHOVER
AGND
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CLK
180º OUT-OF-PHASE
CLK
IF 3.2V < VOUT < 5.5V
Maxim Integrated | 13
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Detailed Description
The MAX20098 is an automotive 2.2MHz synchronous step-down controller IC with 3.5μA IQ, and a fixed output voltage,
or an adjustable 1V to 10V output voltage. In skip mode, with no load, the total supply current is reduced to 3.5μA (typ).
When the controller is disabled, the total current drawn is further reduced to 1μA (typ). Connect EN directly to VBAT, or
to a power-supply sequencing logic.
Fixed 5V Linear Regulator (BIAS)
The internal circuitry of the IC requires a 5V bias supply. An internal 5V linear regulator (BIAS) generates this supply.
Bypass BIAS with a 2.2μF or greater ceramic capacitor to guarantee stability under the full-load condition.
The BIAS linear regulator can source up to 100mA for internal logic, DH, and DL drivers. The estimation of the internal
current requirements for the ICs:
IBIAS = ICC + fSW x (QGDH + QGDL) = 20mA to 50mA (typ) for 400kHz
where ICC is the internal supply current (5mA, typ), fSW is the switching frequency. QGDH is the gate charge of the upper
MOSFET, and QGDL is the gate charge of the lower MOSFET. QG (QG = QGDH + QGDL) is the MOSFET’s total gate
charge (specification limits at VGS = 5V). The BIAS linear regulator is not intended for powering external loads.
Switchover
Switchover typically occurs during skip mode to reduce operating current, but this skip mode switchover can be disabled
by using the ATEG version of the MAX20098. This IC also offers an option to force switchover at all times, when possible.
When switchover occurs, BIAS internally switches to OUT and the internal linear regulator turns off. This configuration
has several advantages:
● Reduces the internal power dissipation of the IC
● Improves low-load efficiency as the internal supply current is scaled down proportionally to the duty cycle
● Switchover occurs when the output voltage is between 3.2V and 5.5V; when voltage is outside this range, the internal
BIAS LDO is used
Undervoltage Lockout (UVLO)
The BIAS input undervoltage-lockout (UVLO) circuitry inhibits switching if the 5V bias supply (BIAS) is below its 2.8V
(typ) UVLO falling threshold. Once the 5V bias supply (BIAS) rises above its UVLO rising threshold and EN enables the
buck controller, the controller start switching and the output voltages begin to ramp up using soft-start.
Buck Controller
The IC provides a buck controller with synchronous rectification. The step-down controller uses a PWM, current-mode
control scheme. External MOSFETs allow for optimized load-current design. Output-current sensing provides an accurate
current limit with a sense resistor, or power dissipation can be reduced by using lossless current sensing across the
inductor.
Soft-Start
Once the buck controller is enabled by driving EN high, the soft-start circuitry gradually ramps up the reference voltage
during soft-start time (tSSTART = 5.4ms (typ)) to reduce the input surge currents during startup. Before the device can
begin the soft-start, the following conditions must be met:
VBIAS exceeds the 3.5V (max) undervoltage lockout threshold VEN goes logic-high
Switching Frequency/External Synchronization
The IC provides an internal oscillator, adjustable from 220kHz to 2.2MHz. 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,
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Maxim Integrated | 14
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
connect a resistor (RFOSC) from FOSC to AGND .
RFOSC =
400kHz × 66kΩ
FOSC
where FOSC is in Hz and RFOSC is in Ω.
The IC 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 ±20% of the internal frequency. The ICs can be used in
parallel for multiphase operation when high power is required. Multiphase operation includes one master and one or more
slave ICs. Synchronization is achieved by connecting the master IC’s clock output SYNCOUT to the slave IC’s clock input
FSYNC. Contact the factory for SYNCOUT options.
Light-Load-Efficiency Skip Mode (VFSYNC = 0V)
Drive FSYNC low to enable skip mode. In skip mode, the IC stops switching until the FB voltage drops below the
reference voltage. Once the FB voltage has dropped below the reference voltage, the IC begins switching until the
inductor current reaches 30% of the maximum current defined by the inductor DCR or output shunt resistor.
Forced-PWM Mode (VFSYNC)
Driving FSYNC high prevents the IC from entering skip mode by disabling the zero-crossing detection of the inductor
current. This forces the low-side gate-driver waveform to constantly be the complement of the high-side gate-driver
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.
Maximum Duty-Cycle Operation
The IC has a maximum duty cycle of 97% (min). The internal logic of the IC looks for approximately 10 consecutive highside FET ON pulses and decides to turn on the low-side FET for 150ns (typ) every 12μs. The input voltage at which the
IC enters 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 IC enters dropout can be approximated as:
VIN = [VOUT + (IOUT × RON_H)] / 0.97
Note: The above equation does not take into account the efficiency and switching frequency, but is a good first-order
approximation. Use the RON_H max number from the data sheet of the respective high-side MOSFET used.
Spread Spectrum
The IC features enhanced EMI performance. It performs ±6% 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. All of this is
controlled by a pin on the IC. When using an external clock source (e.g., driving the FSYNC
input with an external clock), spread spectrum is disabled.
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). During BIAS switchover, the gate drive may be as low as 3.2V. VGS should
be considered when low BIAS voltage is expected. Choose VGS(TH) carefully. 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. 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, use 1nF to 5nF gate capacitors from DL to PGND.
For the high-side drivers, connect a small 1Ω to 5Ω resistor between BST and the bootstrap capacitor.
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Maxim Integrated | 15
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
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. When the switching
frequency range is greater than 1MHz, connect a high-voltage diode between BIAS and BST.
The selected n-channel high-side MOSFET determines the appropriate boost capacitance values (CBST in the Typical
Application Circuit) according to:
CBST = QG/ΔVBST
where QG is the total gate charge of the high-side MOSFET and ΔVBST is the voltage variation allowed on the highside MOSFET driver after turn-on. Choose ΔVBST such that the available gate-drive voltage is not significantly degraded
(e.g., ΔVBST = 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 (VLIMIT = 80mV (typ)), the PWM controller
turns off the high-side MOSFET. The actual maximum load current is less than the peak current-limit threshold by an
amount equal to half 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 (RCS) between the inductor and the output capacitor. Connect CS to the inductor side of
RCS and OUT to the capacitor side. Dimension RCS such that the maximum inductor current (IL (max) = ILOAD (max)
+ 1/2 IRIPPLE (peak-to-peak) induces a voltage of VLIMIT across RCS, 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 current-sense circuit. See the Current-Sense Measurement
section.
Voltage Monitoring (PGOOD)
The IC includes a power monitoring signal (PGOOD) to facilitate power-supply sequencing and supervision. PGOOD
can be used to enable circuits that are supplied by the IC's output voltage rail, or to turn on subsequent supplies. The
PGOOD signal features hysteresis, it stays low until output voltage rises to 95% of the nominal value and is pulled low
only when output voltage falls to 93% of the nominal value. PGOOD also asserts low during soft-start and soft-discharge.
PGOOD goes high impedance when the output voltage is at its nominal value (range). Connect a 10kΩ pullup resistor
from PGOOD to a relevant logic rail to level shift the signal.
Thermal-Overload, Overcurrent, Overvoltage, and Undervoltage Behavior
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the IC. When the junction temperature exceeds +165°C, an
internal thermal sensor shuts down the IC, allowing it to cool. The thermal sensor turns on the IC again after the junction
temperature cools by 20°C.
Overcurrent Protection
If the inductor current on the IC exceeds the maximum current limit programmed at CS and OUT, the respective driver
turns off. In an overcurrent mode, this results in shorter and shorter high-side pulses. A hard short results in a minimum
on-time pulse every clock cycle. Choose the components so they can withstand the short-circuit current if required.
Overvoltage Protection
The IC limits the output voltage of the buck converters by turning off the high-side gate driver at approximately 108% of
the regulated output voltage. The output voltage needs to come back in regulation before the high-side gate driver starts
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Maxim Integrated | 16
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
switching again.
Design Procedure
Effective Input Voltage Range in the Buck Converter
Although the IC 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 typical voltage conversion ratio following Equation:
VOUT
VIN
> 50ns × fSW
where fSW is the switching frequency in hertz. If the desired voltage conversion does not meet the above condition, pulse
skipping occurs to decrease the effective duty cycle. Decrease the switching frequency if constant switching frequency is
required. The same is true for the maximum voltage-conversion ratio.
The maximum voltage-conversion ratio is limited by the maximum duty cycle of 97% and the maximum allowed output
voltage of 10V.
VOUT
< 0.97
VIN − VDROP
where VDROP = IOUT (RON,HS + RDCR) is the sum of the parasitic voltage drops in the high-side path. During low-drop
operation, the IC reduces fSW to ~80kHz. In practice, the above condition should be met with adequate margin for good
load-transient response.
Setting the Output Voltage
Connect FB to BIAS to enable the fixed buck-controller output voltages (5V and 3.3V) set by a preset internal resistive
voltage-divider connected between the feedback (FB) and AGND. To externally adjust the output voltage between 1V
and 10V, connect a resistive divider from the output (OUT) to FB to AGND (see the Typical Application Circuit. Calculate
VOUT
RFB with: RFB2 = RFB1 × [( V
) − 1]
FB
where VFB = 1V (typ) (see the Electrical Characteristics table), RFB2, RFB1 are top and bottom resistors in the feedback
divider.
DC output-accuracy specifications in the Electrical Characteristics table refer to the error comparator’s threshold, VFB =
1V (typ). When the inductor conducts continuously (continuous conduction mode), the IC regulates 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 IC regulates the valley of the
output ripple, so the output voltage has a DC regulation level higher than the error-comparator threshold.
Inductance
The exact inductor value is not critical and can be adjusted to make trade-offs among size, cost, efficiency, and transientresponse requirements:
● Lower inductor values increase LIR, which minimizes size and cost and improves transient response at the cost of
reduced efficiency due to higher peak currents.
● Higher inductance values decrease LIR, which increases efficiency by reducing the RMS current at the cost of
requiring larger output capacitors to meet load-transient specifications.
The ratio of the inductor peak-to-peak AC current to DC average current (LIR) must be selected first. A good initial value
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 determine the inductor value, as shown in the following Equation:
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Maxim Integrated | 17
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
(VIN − VOUT) × D
LMIN1 = f
SW × IOUT × LIR
where VIN, VOUT, and IOUT are typical values (so that efficiency is optimum for typical conditions).
To avoid instability for >50% duty cycle cases, the inductance must satisfy the slope compensation criterion:
VOUT
VSLOPEfSW > 2 × L
AVCSRCS
MIN2
where AVCS is the current sense amplifier gain (typical 13V/V). VSLOPE is VOUT dependent and is given by the equation
below:
VSLOPE
= 105mV for 0V < VOUT ≤ 3V
= 210mV for 3V < VOUT ≤ 5.5V
= 420mV for 5.5V < VOUT
Select the larger of LMIN1 and LMIN2 as LMIN.
Peak Inductor Current
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) +
∆ lINDUCTOR
2
For the selected inductance value, the actual peak-to-peak inductor ripple current (ΔIINDUCTOR) is calculated as follows:
∆ lINDUCTOR =
VOUT(VIN − VOUT)
VIN × fSW × L
where ΔIINDUCTOR 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
The 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 n-channel MOSFETs must be a logic-level type with guaranteed on-resistance specifications at VGS = 4.5V. If the
internal regulator is bypassed (e.g., buck output = 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 = 3.3V when the internal linear regulator is
bypassed. For load currents below ~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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Maxim Integrated | 18
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Current-Sense Measurement
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 1. 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 2) with an equivalent time constant.
INPUT (VIN)
CIN
MAX20098
DH
RCS
L
LX
COUT
DL
PGND
CS
OUT
(A) OUTPUT SERIES RESISTOR SENSING
INPUT (VIN)
CIN
MAX20098
DH
INDUCTOR
L
DCR
R1
R2
LX
DL
PGND
CS
CEQ
COUT
( )
[ ]
R2
RCSHL = R1 + R2 RDCR
1 1
L
RDCR = CEQ R1 + R2
OUT
(B) LOSSLESS INDUCTOR SENSING
Figure 1. Current-Sense Configurations
R2
RCSHL = ( R1 + R2 )RDCR
and
L
1
1
RDCR = C ( R1 + R2 )
EQ
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. If DCR sense is the preferred current-sense method, then the
recommended resistor value for R1 (Figure 2) is ≤ 1kΩ.
Carefully follow the PCB Layout Recommendations to ensure the noise and DC errors do not corrupt the differential
current-sense signals seen by CS and OUT. Place the sense resistor close to the IC with short, direct traces, making a
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Maxim Integrated | 19
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Kelvin-sense connection to the current-sense resistor.
Input Capacitor
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 the input-voltage ripple kept within design
requirements. When using two MAX20098 in parallel, 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 worstcase input-capacitor ripple current is when the converter with the highest output current is on.
The input-voltage ripple is composed of ΔVQ (caused by capacitor discharge) and ΔVESR (caused by the ESR of the
input capacitor). The total voltage ripple is the sum of ΔVQ and ΔVESR that peaks at the end of an on-cycle. Calculate
the input capacitance and ESR required for a specific ripple.
ESR[Ω] =
∆ VESR
(ILOAD(MAX) +
CIN[μF] =
ILOAD(MAX) × (
∆ IP − P
2
VOUT
VIN
)
)
( ∆ VQ × fSW)
× (1 − D)
where:
∆ IP − P =
(VIN − VOUT) × VOUT
VIN × fSW × L
ILOAD(MAX) is the maximum output current in amps, ΔIP-P is the peak-to-peak inductor current in amps, 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.
Output Capacitor
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. 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 shown:
L( ∆ ILOAD(MAX))2
VSAG = 2C
OUT((VIN × DMAX) − (VOUT)
The amount of overshoot (VSOAR) during a full-load to no-load transient due to stored inductor energy can be calculated
as shown in the following equation:
VSOAR =
( ∆ ILOAD(MAX))2L
2COUTVOUT
ESR Considerations
The output-filter capacitor must have low enough equivalent series resistance (ESR) to meet output-ripple and loadtransient requirrements, yet have high enough ESR to satisfy stability requirements. When using high Capacitance low-
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Maxim Integrated | 20
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
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 × ILOAD(MAX) × LIR
In standby mode, the inductor current becomes discontinuous, with peak currents set by the idle-mode current-sense
threshold (VCS,SKIP = 15mV (typ)).
gmc = 1/(AVCS x RCS)
CS
CURRENT-MODE
POWER
MODULATION
OUT
RFB2
ESRCOUT
gm,EA = 500µS
FB
COUT
COMP
ERROR
AMP
RFB1
VREF
30MΩ
RC
CF
CC
Figure 2. Compensation Network
Compensation-Components Calculation
The IC uses a current-mode-control scheme for boost controller. 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 outputcapacitor 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
GAINMOD(dc) = gmc × RLOAD
where RLOAD = VOUT/ILOUT(MAX) in ohms and gmc =1/(AVCS x RDC) in Siemens. AVCS is the voltage gain of the
current-sense amplifier and is typically 13V/V. RDC is the DC resistance of the inductor or the current-sense resistor
in ohms. In a current-mode step-down converter, the output capacitor and the load resistance introduce a pole at the
frequency, as shown below:
1
fpMOD = 2π × C
OUT × RLOAD
The output capacitor and its ESR also introduce a zero:
1
fzMOD = 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 similar 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 500μS (typ), and ROUT,EA is the output resistance of the error amplifier, which is 30MΩ
(typ) (see the Electrical Characteristics table.) 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
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Maxim Integrated | 21
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
near the crossover frequency (fC), where the loop gain equals 1 (0dB).
1
fdpEA = 2π × C × (ROUT, EA + R )
C
C
1
fzEA = 2π × C × R
C
C
1
fpEA = 2π × C × R
F
C
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 shown:
fSW
fpMOD < < fC ≤ 5
At the crossover frequency, the total loop gain must be equal to 1.
VFB
GAINMOD(f ) × V
× GAINEA(f ) = 1
C
c
OUT
GAINEA(fC) = gm, EA × RC
GAINMOD(f ) = GAINMOD(dc) ×
C
fpMOD
fC
Therefore:
VFB
GAINMOD(f ) × V
× gm, EA × RC = 1
C
OUT
Solving for RC:
VOUT
RC = g
m, EA × VFB × GAINMOD(fC)
Set the error-amplifier compensation zero formed by RC and CC at the fpMOD. Calculate the value of CC as shown:
1
CC = 2π × f
pMOD × RC
If fzMOD is less than 5 x fC, add a second capacitor (CF) from COMP to AGND. The value of CF is shown:
1
CF = 2π × f
zMOD × RC
As the load current decreases, the modulator pole also decreases; however, the modulator gain increases accordingly
and the crossover frequency remains the same.
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Maxim Integrated | 22
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Applications Information
PCB Layout Recommendations
Careful PCB layout is critical to achieve low switching losses and clean, stable operation. The switching power stage
requires particular attention (see Figure 3). If possible, mount all power components on the top side of the board, with
their ground terminals flush against one another. Follow these guidelines for good PCB layout:
● BST diode footprint can be added if future use of a Schottky is expected.
● Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free
operation.
● Keep the power traces and load connections short. This practice is essential for high efficiency. Using thick copper
PCBs (2oz vs. 1oz) can enhance full-load efficiency by 1% or more. 2oz is recommended for higher currents such as
20A.
● Minimize current-sensing errors by connecting CS and OUT. Use kelvin sensing directly across the current-sense
resistor (RCS).
● Route high-speed switching nodes (BST, LX, DH, and DL) away from sensitive analog areas (FB, CS, and OUT).
Layout Procedure
1. Place the power components first, with ground terminals adjacent (low-side FET, CIN, COUT). If possible, make all
these connections on the top layer with wide, copper-filled areas. Mount the controller IC adjacent to the low-side
MOSFET, preferably on the back side opposite DL and DH to keep LX, PGND, DH, and the DL gate-drive lines short
and wide. To keep the driver impedance low and for proper adaptive dead-time sensing, the DL and DH gate traces
must be short and wide (50 mils to 100 mils wide if the MOSFET is 1in from the controller IC).
2. Group the gate-drive components (BST diode and capacitor and LDO bypass capacitor, BIAS) together as close as
possible to the controller IC. Be aware that gate currents of up to 1A flow from the bootstrap capacitor to BST, from
DH to the gate of the external HS switch, and from the LX pin to the inductor. Up to 100mA of current flows from the
BIAS capacitor through the bootstrap diode to the bootstrap capacitor. Dimension those traces accordingly.
3. Make the DC-DC controller ground connections as shown in Figure 3. This diagram can be viewed as having two
separate ground planes: power ground (where all the high-power components go), and an analog ground plane for
sensitive analog components. The analog ground plane and power ground plane must meet only at a single point
directly under the IC.
4. Connect the output power planes directly to the output filter capacitor’s positive and negative terminals with multiple
vias. Place the entire DC-DC converter circuit as close as possible to the load.
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Maxim Integrated | 23
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
SMALL
INPUT
LOOP
LOW SIDE
HIGH SIDE
MOSFET (QH) MOSFET (QL)
INDUCTOR
VIN
CIN CIN
AGND-PGND
CONNECTION
UNDER THE IC
GND
CBIAS
COUT
MAX20098
OUT/CS
DIFFERENTIAL
ROUTING
COUT
KELVIN-SENSE
VIAS UNDER THE
SENSE RESISTOR
(RCS)
VOUT
Figure 3. Layout Example
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Maxim Integrated | 24
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Typical Application Circuits
VOUT
L
RCS
VBAT
COUT
CBST
BST
DH
LX
DL
PGND
SUP
CIN
PGOOD
EN
MAX20098
CS
FSYNC/SYNCOUT
FOSC
OUT
RFOSC
AGND
CBIAS
BIAS
FB
COMP
CF
RC
CC
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Maxim Integrated | 25
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Ordering Information
PART
PINPACKAGE
VOUT
ADJUSTABLE
FIXED
SPREAD
SPECTRUM
SWITCHOVER IN
FPWM
SWITCHOVER IN
SKIP
SYNC/
SYNCOUT
MAX20098ATEA/
VY+
16 SW TQFNEP*
1V to 10V
5V
Off
On
On
SYNC
MAX20098ATEB/
VY+
16 SW TQFNEP*
1V to 10V
3.3V
Off
On
On
SYNC
MAX20098ATEC/
VY+
16 SW TQFNEP*
1V to 10V
5V
On
On
On
SYNC
MAX20098ATED/
VY+
16 SW TQFNEP*
1V to 10V
3.3V
On
On
On
SYNC
MAX20098ATEE/
VY+
16 SW TQFNEP*
1V to 10V
3.3V
Off
Off
On
SYNC
MAX20098ATEF/
VY+
16 SW TQFNEP*
1V to 10V
3.3V
On
Off
On
SYNC
MAX20098ATEG/
VY+
16 SW TQFNEP*
1V to 10V
3.3V
On
Off
Off
SYNC
Note: All parts operate over the -40°C to +125°C automotive temperature range.
/V denotes an automotive qualified part.
+Denotes a lead(Pb)-free/RoHS-compliant package. SW = Side-wettable TQFN package.
*EP = Exposed pad.
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Maxim Integrated | 26
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
Revision History
REVISION
NUMBER
REVISION
DATE
0
10/18
Initial release
9/17
Updated Block Diagram, pin 15 in Pin Description table, PCB Layout
Recommendations section, and Typical Application Circuit
10/17
Updated Electrical Characteristics table (adding a new Note 4 and renumbering
the remaining notes); added new TOC18 in Typical Operating Characteristics
section; added new Equation 2 in Switching Frequency/External Synchronization
section, and renumbered the remaining equations
2–4, 8, 10–17
10/17
Changed derating for 16 SW TQFN in Absolute Maximum Ratings section from
28.8mW/°C to 20.8mW/°C; updated pin 3 in Pin Description table; updated Block
Diagram; updated the last bullet in Switchover and addedSwitchover 2nd
sentence in MOSFET Gate Drivers (DH and DL) sections; removed future
product status from MAX20098ATEE/VY+ in Ordering Information table
2, 7, 9–11, 20
1
2
3
3.1
PAGES
CHANGED
DESCRIPTION
—
8, 9, 18, 19
Corrected revision date on first page
1
1/18
Changed Minimum On-Time in Benefits and Features from 40ns to 50ns
1
1/18
Removed future product status from MAX20098ATEB/VY+, MAX20098ATED/
VY+, and MAX20098ATEF/VY+ in Ordering Information table
20
6
3/18
Updated title, General Description, Benefits and Features, Notes in Electrical
Characteristics table, TOC 4, Fixed 5V Linear Regulator (BIAS), Switchover,
MOSFET Gate Drivers (DH and DL), Current Limiting and Current-Sense Inputs
(OUT and CS), Effective Input Voltage Range in the Buck Converter, Setting the
Output Voltage, Input Capacitor, Figure 2 caption , and PCB Layout
Recommendations sections
7
5/18
Removed future part designation for MAX20098ATEC/VY+
8
9/18
Updated Pin Description and High-Side Gate-Driver Supply (BST) sections
11/18
Updated Electrical Characteristics table (FSYNC Frequency Range), TOC18 in
Typical Operating Characteristics section, and Switching Frequency/External
Synchronization section; updated Ordering Information table and added MAX20098ATEG/VY+
3, 6, 10, 11, 20
4/19
Updated the data sheet title ( added “Automotive”), Benefits and Features,
Absolute Maximum Ratings, Package Thermal Characteristics, Electrical
Characteristics (globals, table, and added Note 5), Pin Description table.
Updated Switchover and Current LimitingSwitchover and Current-Sense Inputs
(OUT and CS) in the Detailed Description section
1-4, 6, 10, 12
4
5
9
10
1–21
20
8, 11
11
6/19
Updated Electrical Characteristics and Detailed Description
3, 10
12
10/19
Updated TOC3 and TOC16 in Typical Operating Characteristics section 5
5, 6
13
7/20
Formula labels/formatting, update Benefits and Features to 1.1%, remove
Electrical Characteristics Note 4, switchover range in Block Diagram, Inductance
guidance, Layout Example
14
8/20
Corrected units in Electrical Characteristics
12/20
Updated Continuous Power dissipation and derating value in Absolute Maximum
Ratings, Corrected symbol and units in Electrical Characteristics, Corrected
units and edited text formatting in Switching Frequency, Edited Voltage
monitoring description, Setting the output voltage, Current sense measurements
, Corrected formula in Input capacitor , edited the figure on compensation
network and edited formatting in Compensation-Component Calculation in
Detailed Descriptions , Edited formatting in PCB Layout Recommendations in
Applications Information
15
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
1, 6, 7, 12-24
6, 7
5, 6, 14-16, 18-22
© 2021 Maxim Integrated Products, Inc.
MAX20098
Versatile Automotive 36V 2.2MHz Buck Controller
with 3.5μA IQ
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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 specifications without notice at any time. The parametric values (min and max
limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2021 Maxim Integrated Products, Inc.
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