Click here to ask about the production status of specific part numbers.
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass
Mode
General Description
Benefits and Features
The MAX25206/MAX25207/MAX25208 are automotive
2.2MHz synchronous step-down controllers with 7μA IQ.
These devices operate with an input voltage supply from
3.5V to 60V (MAX25206/MAX25207) and 70V
(MAX25208). They can operate in drop-out condition by
running at 99% (typ) duty cycle. These controllers are 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. The MAX25207 has an optional bypass mode,
which allows 100% high-side switch on until step-down
function is needed during automotive transients.
● Meets Stringent Automotive OEM Module Power
Consumption and Performance Specifications
• 7µA Quiescent Current in Skip Mode
• Fixed 5.0V/3.3V or Adjustable 0.7V to 20V Output
• ±1.5% Output-Voltage Accuracy for 5V Fixed
Setting
The MAX25206/MAX25207/MAX25208 step-down controllers operate at a frequency up to 2.2MHz to allow small
external components, reduced output ripple, and to eliminate AM band interference. The switching frequency is
resistor adjustable (220 kHz to 2200 kHz). SYNC input
programmability enables three frequency modes for optimized performance: forced fixed-frequency operation (FPWM), skip mode with ultra-low quiescent current, and synchronization to an external clock. The IC also provides
SYNCOUT output to enable two controllers to operate
in parallel. The MAX25206/MAX25207/MAX25208 have a
pin-selectable spread-spectrum option for frequency modulation to minimize EMI.
The MAX25206/MAX25207/MAX25208 feature a PGOOD
monitor and undervoltage lockout. Protection features include cycle-by-cycle current limit and thermal shutdown.
These controllers are specified for operation over the
-40°C to +125°C automotive temperature range.
Applications
● Infotainment Systems
● 48V Systems
● General Purpose Point of Load (POL)
● Enables Crank-Ready Designs
• Wide Input Supply Range from 3.5V to 60V/70V
● 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
• 2.2MHz Step-Down Controller
• 180 Degrees Out-of-Phase SYNCOUT Output for
Synchronization
• Current-Mode Controller with Forced-Continuous
and Skip Modes
• Thermally Enhanced 20-Pin Side-Wettable (SW)
4mm x 4mm TQFN-EP Package
● Protection Features Improve System Reliability
• Supply Undervoltage Lockout
• Output Overvoltage and Undervoltage Monitoring
• Overtemperature and Short-Circuit Protection
• -40ºC to +125ºC Grade 1 Automotive Temperature
Range
Ordering Information appears at end of datasheet.
19-100800; Rev 0; 8/20
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Simplified Block Diagram
L
RCS
VBAT
VOUT
-ORVBAT – I*(RDS+RDCR+RCS)
COUT
DL
LX
BST
ENBK
(MAX25207 ONLY)
SUP
CIN
DH
CBST
PGND
CS
EN
MAX25206/7/8
FSYNC
OUT
FB
SYNCOUT
FOSC
COMP
CBIAS
PGOOD
BIAS
AGND
RFOSC
RC
CF
CC
www.maximintegrated.com
Maxim Integrated | 2
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
TABLE OF CONTENTS
General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Benefits and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Simplified Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Absolute Maximum Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
20 SW TQFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical Operating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Pin Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
MAX25206/MAX25208 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
MAX25207 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Functional Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Fixed 5V Linear Regulator (BIAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
BIAS Switchover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Undervoltage Lockout (UVLO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Buck Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Bypass Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Bypass Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Soft-Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Switching Frequency/External Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Skip Mode for Light-Load-Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Forced-PWM Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Maximum Duty-Cycle Operation in Buck Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Spread Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
MOSFET Gate Drivers (DH and DL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
High-Side Gate-Driver Supply (BST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Current Limiting and Current-Sense Inputs (OUT and CS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Voltage Monitoring (PGOOD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Thermal-Overload Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Overvoltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Design Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
www.maximintegrated.com
Maxim Integrated | 3
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
TABLE OF CONTENTS (CONTINUED)
Effective Input Voltage Range in the Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Setting the Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Inductor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Peak Inductor Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
MOSFET Selection in Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Current-Sense Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Input Capacitor in Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output Capacitor in Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Control Loop / Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Layout Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Typical Application Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Application Circuit 1: 5VOUT 2.2MHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Application Circuit 2: 16VOUT 440kHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Application Circuit 3: 12VOUT 2.2MHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
www.maximintegrated.com
Maxim Integrated | 4
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
LIST OF FIGURES
Figure 1. Bypass Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 2. Current-Sense Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 3. Compensation Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 4. Layout Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
www.maximintegrated.com
Maxim Integrated | 5
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Absolute Maximum Ratings
SUP, EN, LX to PGND (MAX25206, MAX25207) .... -0.3V to 65V
SUP, EN, LX to PGND (MAX25208) ........................ -0.3V to 75V
OUT to AGND........................................................... -0.3V to 22V
CS to OUT ............................................................... -0.3V to 0.3V
SYNCOUT, SPS, FOSC, COMP, FB, ENBK to AGND ....-0.3V to
BIAS + 0.3V
BIAS to AGND ............................................................ -0.3V to 6V
PGOOD, FSYNC to AGND......................................... -0.3V to 6V
DL to PGND ............................................... -.0.3V to BIAS + 0.3V
BST to LX ................................................................... -0.3V to 6V
DH to LX ......................................................... -0.3V to BST+0.3V
PGND to AGND ....................................................... -0.3V to 0.3V
Package Thermal Characteristics
T2044Y+6C
Continuous Power Dissipation
TQFN (derate 28mW/°C above +70°C) ...............2260mW
Operating Temperature Range....................-40°C to +125°C
Junction Temperature................................................ +150°C
Storage Temperature Range .......................-65°C to +150°C
Soldering Temperature (reflow) ................................. +260°C
Lead Temperature (soldering, 10s) ...........................+300°C
Note 1: During initial startup, VSUP, rising must cross 6V. The normal operating range is then valid.
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.
Recommended Operating Conditions
PARAMETER
SYMBOL
CONDITION
Ambient Temperature Range
TYPICAL
RANGE
UNIT
-40 to
+125
ºC
Note: These limits are not guaranteed.
Package Information
20 SW TQFN
Package Code
T2044Y+6C
Outline Number
21-100388
Land Pattern Number
90-100132
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θJA)
35.4 ºC/W
Junction to Case (θJC)
4 ºC/W
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates
RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal
considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VSUP = 24V (MAX25206, MAX25207)/48V (MAX25208), VEN = VSUP, CSUP = 4.7μF, CBIAS = 2.2μF, CBST = 0.1μF, RFOSC = 12kΩ,
TJ = -40°C to +150°C, unless otherwise noted. Typical values are at TA = +25°C. (Note 2 and 5))
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SYNCHRONOUS STEP DOWN CONVERTER
Supply Voltage Range
www.maximintegrated.com
VSUP
Normal Operation (MAX25206 and
MAX25207) (Note 3)
3.5
60
Normal Operation (MAX25208) (Note 3)
3.5
70
V
Maxim Integrated | 6
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Electrical Characteristics (continued)
(VSUP = 24V (MAX25206, MAX25207)/48V (MAX25208), VEN = VSUP, CSUP = 4.7μF, CBIAS = 2.2μF, CBST = 0.1μF, RFOSC = 12kΩ,
TJ = -40°C to +150°C, unless otherwise noted. Typical values are at TA = +25°C. (Note 2 and 5))
PARAMETER
SYMBOL
Output Overvoltage
Threshold
Supply Current
ISUP
CONDITIONS
VOUT
Output Voltage
Adjustable Range
Detected with respect to VFB Falling
105
VFB
Feedback Leakage
Current
IFB
Feedback Line
Regulation Error
Transconductance (from
FB to COMP)
gm, EA
Dead Time
Max Duty Cycle
6
VEN = VSUP, VOUT = 5V, No Switching,
MAX25206/8
7
11
VEN = VSUP = 14V, MAX25207 in bypass
mode
3
VFB = VBIAS, VOUT = 5V, skip mode
tON,MIN
PWM Switching
Frequency Range
fSW
Switching Frequency
Accuracy
4.925
5
µA
mA
5.075
4.9
5
5.1
VFB = VBIAS, VOUT = 3.3V, PWM mode
3.234
3.3
3.366
VFB = VBIAS, VOUT = 3.3V, skip mode
3.234
3.3
3.366
0.7
UNITS
%
1
V
20
V
0.7
0.715
V
TA = +25°C
0.01
1
µA
VSUP = 3.5V to 60V, VFB = 0.7V
0.01
0.689
VFB = 0.7V, VBIAS = 5V
220
450
DL low to DH Rising
15
DH low to DL Rising
15
Buck
Minimum On-Time
MAX
VEN = 0V
Buck
Regulated Feedback
Voltage
TYP
107
VFB = VBIAS, VOUT = 5V, PWM mode
Buck Fixed Output
Voltage
MIN
Detected with respect to VFB Rising
650
µS
ns
97
Buck
Programmable
%/V
%
50
0.22
ns
2.2
MHz
RFOSC = 12kΩ, VBIAS = 5V, 3.3V
2
2.2
2.4
MHz
VLIMIT
VCS – VOUT; VBIAS = 5V, VOUT ≥ 2.5V
71
80
89
mV
tSOFT-START
Buck, fixed soft-start time regardless of
frequency.
3.7
ms
LX Leakage Current
VSUP = 6V, VLX = VPGND or VSUP, TA =
25°C
0.01
µA
DH Pullup Resistance
VBIAS = 5V, IDH = -100mA
2.7
Ω
DH Pulldown
Resistance
VBIAS = 5V, IDH = 100mA
1
Ω
DL Pullup Resistance
VBIAS = 5V, IDL = -100mA
2.2
Ω
DL Pulldown Resistance
VBIAS = 5V, IDL = 100mA
1
Ω
CS Current-Limit
Voltage Threshold
Soft-Start Ramp Time
www.maximintegrated.com
Maxim Integrated | 7
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Electrical Characteristics (continued)
(VSUP = 24V (MAX25206, MAX25207)/48V (MAX25208), VEN = VSUP, CSUP = 4.7μF, CBIAS = 2.2μF, CBST = 0.1μF, RFOSC = 12kΩ,
TJ = -40°C to +150°C, unless otherwise noted. Typical values are at TA = +25°C. (Note 2 and 5))
PARAMETER
PGOOD UV Threshold
SYMBOL
CONDITIONS
PGOOD_H
% of target VOUT, Rising
PGOOD_F
% of target VOUT, Falling
MIN
TYP
MAX
95
90.5
PGOOD Leakage
Current
VPGOOD = 5V, TA = 25°C
PGOOD Output Low
Voltage
ISINK = 1mA
PGOOD Debounce
Time
OV/UV Fault Detection, Rising and
Falling
PGOOD Timeout
OTP Option (default 0ms) rising
0.5
Rising threshold where buck starts (14V
to 18V, 0.5V Steps) MAX25207
-3
UNITS
%
93
95.5
0.01
1
µA
0.2
V
32
µs
ms
Bypass Mode
Bypass Mode Threshold
VBYP
Hysteresis
3
0.7
ENBK Threshold, High
VIH
ENBK Threshold, Low
VIL
V
1.4
V
0.4
ENBK Internal Pulldown
%
620
V
kΩ
FSYNC INPUT
FSYNC Frequency
Range
FSYNC Switching
Thresholds
fOSC = 2.2MHz, minimum sync pulse >
(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
ns
V
Low Threshold
0.4
V
INTERNAL LDO BIAS
Internal BIAS Voltage
VSUP > 6V
5
VBIAS Rising
BIAS UVLO Threshold
VBIAS Falling
3.1
2.6
V
3.5
2.8
V
THERMAL OVERLOAD
Thermal Shutdown
Temperature
TJ rising (Note 4)
165
°C
Thermal Shutdown
Hysteresis
(Note 4)
20
°C
Logic Levels
EN High Threshold
EN
EN Low Threshold
EN
EN Input Bias Current
EN logic input only, TA = 25°C
SPS Threshold, High
VIH,SPS
SPS Threshold, Low
VIL,SPS
www.maximintegrated.com
1.4
V
0.01
0.4
V
1
μA
1.4
V
0.4
V
Maxim Integrated | 8
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Electrical Characteristics (continued)
(VSUP = 24V (MAX25206, MAX25207)/48V (MAX25208), VEN = VSUP, CSUP = 4.7μF, CBIAS = 2.2μF, CBST = 0.1μF, RFOSC = 12kΩ,
TJ = -40°C to +150°C, unless otherwise noted. Typical values are at TA = +25°C. (Note 2 and 5))
PARAMETER
SYMBOL
CONDITIONS
SPS Internal Pulldown
MIN
TYP
MAX
620
UNITS
kΩ
SYNCOUT and Spread Spectrum Logic
SYNCOUT Low Voltage
ISINK = 5mA
SYNCOUT Leakage
Current
TA = 25°C
Spread Spectrum
±6
0.4
V
1
µA
% of
fOSC
Note 2: Limits are 100% production tested at TA = +25oC. 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 6V. 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.
www.maximintegrated.com
Maxim Integrated | 9
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Typical Operating Characteristics
www.maximintegrated.com
Maxim Integrated | 10
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Typical Operating Characteristics (continued)
www.maximintegrated.com
Maxim Integrated | 11
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Pin Configurations
MAX25206/MAX25208
DL
PGND
BIAS
NC
NC
TOP VIEW
15
14
13
12
11
LX
16
10
CS
DH
17
9
OUT
BST
18
8
FB
SUP
19
7
AGND
EN
20
6
COMP
MAX25206/8
+
5
PGOOD
4
FOSC
3
FSYNC
2
SYNCOUT
SPS
1
TQFN
4mm × 4mm
MAX25207
DL
PGND
BIAS
ENBK
NC
TOP VIEW
15
14
13
12
11
LX
16
10
CS
DH
17
9
OUT
BST
18
8
FB
SUP
19
7
AGND
EN
20
6
COMP
MAX25207
2
3
4
5
FSYNC
FOSC
PGOOD
SPS
1
SYNCOUT
+
TQFN
4mm × 4mm
Pin Description
PIN
MAX25206/
MAX25208
MAX25207
1
1
www.maximintegrated.com
NAME
FUNCTION
SPS
Spread Spectrum Enable Pin. Pull to logic high for spread spectrum enabled. Pull
to ground to disable spread spectrum.
Maxim Integrated | 12
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Pin Description (continued)
PIN
MAX25206/
MAX25208
MAX25207
2
2
NAME
FUNCTION
SYNCOUT
Clock Output. SYNCOUT outputs 180 degrees out of phase relative to the internal
oscillator.
External Clock Synchronization Input. Connect FSYNC to AGND to enable skip
mode of operation (MAX25206/MAX25208 only). Connect to BIAS or an external
clock to enable forced-PWM mode of operation. Tie FSYNC high for MAX25207. If
external clock synchronization is required for MAX25207, contact factory for
review. See Switching Frequency/External Synchronization section for additional
information.
3
3
FSYNC
4
4
FOSC
Frequency Setting Input. Connect a resistor to FOSC to set the switching
frequency of the DC-DC controller.
Open-Drain Power-Good Output for Buck Controller. PGOOD asserts low during
soft-start and in shutdown. PGOOD becomes high impedance when OUT is in
regulation. Actively pulled down if OUT is outside the regulation window. For
MAX25207, PGOOD is always high impedance in bypass mode. To obtain a logic
signal, pull up PGOOD with an external resistor connected to a positive voltage
lower than 5.5V.
5
5
PGOOD
6
6
COMP
Buck Controller Error Amplifier Output. Connect an RC network between COMP
and AGND to compensate the buck controller.
7
7
AGND
Analog Ground for Controller
8
8
FB
Feedback Input for Buck Controller. Connect FB to BIAS for the fixed output or to
a resistor divider between OUT and GND to adjust the output voltage between
0.7V and 20V. In adjustable mode, FB regulates to 0.7V (typ).
Output Sense and Negative Current-Sense Input for Buck Controller. When using
the internal preset 5V feedback-divider (FB = BIAS), the controller uses OUT to
sense the output voltage. Connect OUT to the negative terminal of the currentsense element. See Current Limiting and Current Sense Inputs and Current Sense
Measurement sections.
9
9
OUT
10
10
CS
Positive Current-Sense Input for Buck Controller. Connect CS to the positive
terminal of the current-sense element. See Current Limiting and Current Sense
Inputs and Current Sense Measurement sections.
11
11
NC
No Connect
12
12
NC/ENBK
Force Buck Mode Pin. For bypass-enabled part MAX25207, pull to logic high to
force buck mode, pull to ground to let the part decide operation mode (buck or
bypass) based on supply voltage. Connect to ground for MAX25206/MAX25208.
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 gate drivers. See Fixed 5V Linear Regulator (BIAS) and BIAS
Switchover sections.
13
13
BIAS
14
14
PGND
15
15
DL
Low-Side Gate Driver Output. DL output voltage swings from VPGND to VBIAS.
16
16
LX
Inductor Connection. Connect LX to the switched side of the inductor.
17
17
DH
High-Side Gate Driver Output
18
18
BST
Bootstrap capacitor connection. Connect a ceramic capacitor between BST and
LX. See High-Side Gate-Driver Supply (BST) section.
www.maximintegrated.com
Power Ground for Controller
Maxim Integrated | 13
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Pin Description (continued)
PIN
NAME
FUNCTION
19
SUP
Supply Input for IC. Bypass to ground with a 2.2μF or larger capacitor near the IC.
Connect to buck power stage input voltage (VIN). Power stage needs additional
input capacitors (CIN).
20
EN
MAX25206/
MAX25208
MAX25207
19
20
EP
EP
www.maximintegrated.com
–
High-Voltage Tolerant, Active-High Digital Enable Input for 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, 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 | 14
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Functional Diagrams
Block Diagram
PGOOD
COMP
ENBK
SUP
OV
UV
FB
FEEDBACK
SELECT
+
+
SOFT
START
CHARGE
PUMP
EAMP
BST
REF = 0.7V
PWM
COMP
OUT
CS
GATE DRIVE &
LOGIC
PWM
80mV (typ)
CSA
DH
LX
EN
ILIM
SLOPE
COMP
DL
ILIM
COMP
LX
PGND
ZERO
CROSS
FSYNC
SELECT
LOGIC
FSYNC
SUP
FOSC
SPS
BIAS
OSCILLATOR
CLK
OUT
INTERNAL LDO
/SWITCHOVER
BIAS
SYNCOUT
AGND
www.maximintegrated.com
Maxim Integrated | 15
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Detailed Description
The MAX25206/MAX25207/MAX25208 are automotive 2.2MHz synchronous step-down controller ICs with 5V/3.3V fixed
or adjustable 0.7V to 20V output voltage. The MAX25207 offers a bypass mode that delivers high-efficiency, high-side
switch-on mode.
In skip mode (MAX25206/8), with no load, the total supply current is reduced to 7μA (typ). When the controller is disabled,
the total current drawn is further reduced to 1μA (typ).
To enable the IC, connect EN directly to VSUP, 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 to PGND with a 2.2μF or greater ceramic capacitor.
The BIAS linear regulator can source up to 100mA for internal logic, DH, and DL drivers. The internal current consumption
in the IC is estimated using the following equation:
IBIAS = ICC + fSW × (QGDH + QGDL) = 20mA to 50mA (typ) for 400kHz
where ICC is the internal supply current (3mA, 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. The BIAS linear regulator is not intended for powering
external loads.
BIAS Switchover
MAX25206/MAX25208 have a BIAS switchover option available to reduce the power dissipation in the internal BIAS
regulator if the target output voltage is in the BIAS switchover range (3.1V to 5.2V). In BIAS switchover, the internal BIAS
regulator is switched off and the BIAS is supplied from the OUT pin.
MAX25207 does not feature BIAS switchover.
Undervoltage Lockout (UVLO)
The BIAS undervoltage-lockout (UVLO) circuitry inhibits switching if the BIAS voltage is below the BIAS UVLO threshold.
Once BIAS rises above its UVLO rising threshold and EN is high, the controller starts switching and the output is allowed
to ramp up.
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 an external sense resistor, or power dissipation can be reduced by using lossless current sensing across
the inductor.
Bypass Mode
To maximize the efficiency of the front-end conversion stage, MAX25207 comes with a bypass mode. The IC enters
bypass mode when the input voltage falls 0.7V below the bypass threshold (VSUP < VBYP - 0.7V). In this mode, the IC
utilizes an internal charge pump to maintain 100% duty cycle on the high-side MOSFET. When VSUP > VBYP, the IC
quickly resumes buck mode operation and regulates the output voltage.
MAX25207 allows the customer to achieve high efficiency (no switching) at normal battery voltage (bypass mode) and
provides a regulated output voltage during high line conditions. This protects the downstream parts from high voltage
battery transients. MAX25207 also comes with an Enable Buck (ENBK) logic input which forces buck mode operation
regardless of VSUP when driven high. See Bypass Timing Diagram for valid states and corresponding output.
www.maximintegrated.com
Maxim Integrated | 16
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Bypass Timing Diagram
1
0
VENBK
VBYP
VSUP
VOUT ≈ VSUP
VOUT = INTERNALLY PROGRAMMED OR SET
USING EXTERNAL RESISTOR DIVIDER
VOUT
BYPASS
BUCK
BYPASS
BUCK
Figure 1. Bypass Timing
VBYP: Bypass voltage threshold. This is an OTP programmable threshold for bypass decision making in MAX25207.
VOUT: Output voltage. Buck mode output voltage is internally programmed or set using external resistor divider. Bypass
mode output voltage is approximately equal to the supply voltage.
VENBK: Enable Buck. A logic high at ENBK pin forces buck mode regardless of VSUP.
Soft-Start
The soft-start circuitry gradually ramps up the reference voltage during soft-start time (tSOFT-START) to reduce the input
inrush current during startup. Before the device can begin soft-start, the following conditions must be met:
● VBIAS exceeds the BIAS UVLO threshold
● VEN is logic high
During soft-start, PGOOD asserts low until an internal Soft-Start Done signal is received.
The MAX25207 always starts up in buck mode. The bypass mode determination is made after soft-start is complete.
Switching Frequency/External Synchronization
The IC provides an internal oscillator, adjustable from 220kHz to 2.2MHz, set with an external resistor connected to
FOSC. High-frequency operation results in smaller component size at the cost of 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:
RFOSC =
400kHz × 66kΩ
1 + 60ns × (2.2MHz − fOSC)
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 IC and one or more slave ICs. Synchronization is achieved by connecting the master IC's clock output SYNCOUT
to the slave ICs' clock input FSYNC. Connect the COMP pin of the slave IC to that of the master. The error amplifier of
the slave IC is disabled and the master IC will drive compensation adjustments. (Contact factory for slave versions of the
IC)
Skip Mode for Light-Load-Efficiency
Drive FSYNC low to enable skip mode. In skip mode, the inductor current is not allowed to turn negative. Once inductor
www.maximintegrated.com
Maxim Integrated | 17
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
current reaches zero, the low-side MOSFET is turned off. The high-side MOSFET is not turned on again until FB voltage
drops below the reference voltage. Once FB voltage drops below the reference voltage, the high-side MOSFET is turned
on until the inductor current reaches 20% of the current limit threshold.
Forced-PWM Mode
Driving FSYNC high or external synchronization prevents the IC from entering skip mode by disabling the zero-crossing
detection of the inductor current. This allows the inductor current to reverse at light load and during transients.
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 in Buck Mode
The IC has a maximum duty cycle of 99% (typ) (97% (min)) in buck mode. In maximum duty cycle operation, the internal
logic of the IC monitors approximately 10 consecutive high-side FET ON pulses and then turns on the low-side FET for
150ns (typ) every 12μs if bypass mode is not selected. The input voltage at which the IC enters this dropout condition
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 using the following equation:
VIN ≈
(
VOUT + IOUT RDS(ON) + RDCR
0.97
)
where RDS(ON) is the on-resistance of the high-side MOSFET.
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. A logic high
on SPS pin enables spread spectrum. Using external clock source (e.g., driving the FSYNC input with an external clock)
disables spread spectrum.
MOSFET Gate Drivers (DH and DL)
The high-side n-channel MOSFET driver (DH) is powered from capacitor at BST, while the low-side driver (DL) is
powered from BIAS. In BIAS switchover operation, the gate drive supply voltage may be low depending on the target
VOUT. The impact of low gate drive voltage in BIAS switchover designs should be considered when selecting MOSFETs.
A shoot-through protection circuit monitors the gate-to-source voltage of the external MOSFETs to prevent simultaneous
turn on of high-side and low-side MOSFETs. There must be a low-resistance, low-inductance forward and return path
from the drivers to the MOSFET gates for the protection circuits to work properly.
It may be necessary to decrease the slew rate for the gate drivers to reduce switching noise. For the high-side driver,
connect a small 1Ω to 5Ω resistor between DH and the gate of the high-side MOSFET. For the low-side driver, use a 1Ω
resistor between DL and the gate of the low-side MOSFET.
High-Side Gate-Driver Supply (BST)
The high-side MOSFET driver is supplied by a bootstrap capacitor (CBST) connected between BST and LX pins.
CBST re-charges from BIAS, through an internal switch, when the low-side MOSFET is on bringing LX to ground. For
MAX25207 in bypass mode, CBST is kept charged using an internal charge pump.
The bootstrap capacitance (CBST) is selected to limit the voltage drop on CBST during high-side MOSFET turn on, as
given by:
CBST = QG / ∆ VBST
where QG is the total gate charge of the high-side MOSFET and ∆VBST (100mV to 300mV) is the voltage ripple on CBST.
A 100nF low-ESR ceramic capacitor is sufficient in most cases.
www.maximintegrated.com
Maxim Integrated | 18
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Current Limiting and Current-Sense Inputs (OUT and CS)
The current-sense amplifier (CSA) uses differential current-sense inputs (OUT and CS) to sense the inductor current.
For normal buck operation, this sensed signal is used for peak current mode control. If the current-sense signal exceeds
the current-limit threshold (VLIMIT = 80mV (typ)), the PWM controller turns off the high-side MOSFET. The maximum
load current is less than the peak current-limit threshold by 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 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 output capacitor side. Select RCS such that
ΔIL
VLIMIT
ILOAD + 2 < R
CS
where ΔIL is the inductor current ripple.
Inductor DCR sensing can be used for higher efficiency but can result in up to 30% error in current limit threshold due to
variation in inductor DCR over temperature. See Current-Sense Measurement for information on DCR sensing network
design.
Voltage Monitoring (PGOOD)
PGOOD is an open-drain power-good output for the buck controller that is pulled low when the output voltage is outside
the PGOOD regulation window. PGOOD is low during soft-start, soft-discharge, or when the controller is disabled (EN is
low). Connect a 10kΩ (typ) pullup resistor from PGOOD to the relevant logic rail to level shift the signal.
For MAX25207, PGOOD is always high when operating in bypass mode.
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 sensed voltage across CS/OUT exceeds the current limit threshold (VLIMIT = 80mV (typ)), the high-side driver (DH)
turns off and the low-side driver (DL) turns on. The high side MOSFET does not turn on again until voltage across CS/
OUT drops below the current-limit threshold.
MAX25207 continues to offer current-limit protection in bypass mode.
The part enters hiccup mode if the output voltage falls below the hiccup threshold (50% of target VOUT for MAX25206/
MAX25208, 20% of target VOUT for MAX25207).
Overvoltage Protection
In case of an overvoltage on the output, the controller turns off high- and low-side MOSFET drivers (DH/DL). Switching
resumes when the output voltage comes back into regulation.
www.maximintegrated.com
Maxim Integrated | 19
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Applications Information
Design Procedure
Effective Input Voltage Range in the Buck Converter
Although the IC can operate from input supplies up to 60V/70V and regulate down to 0.7V, the minimum voltage
conversion ratio for fixed frequency operation is limited by the minimum controllable on-time (tON,MIN):
VOUT
VIN
> tON, MIN × fSW
where fSW is the switching frequency. If the desired voltage conversion does not meet the above condition, pulse skipping
occurs to maintain regulation. Decrease the switching frequency if constant switching frequency is required at higher
input voltages.
The maximum voltage conversion ratio in buck mode of operation is limited by the maximum duty cycle (see Maximum
Duty-Cycle Operation in Buck Mode). During low-drop operation, the IC reduces the switching frequency (fSW) to
~80kHz.
MAX25207 provides 100% duty cycle operation in bypass mode.
Setting the Output Voltage
Connect FB to BIAS to enable the fixed buck-controller output voltage (5V or 3.3V) set by a preset internal resistor
voltage-divider connected between OUT and AGND. To externally adjust the output voltage between 0.7V and 20V,
connect a resistor divider from the output (OUT) to FB to AGND.
RFB2
RFB1
=
( )
VOUT
VFB
−1
where VFB = 0.7V (typ) (see the Electrical Characteristics) and RFB2, RFB1 are top and bottom resistors in the feedback
divider.
In skip mode, the IC regulates the valley of the output ripple.
Inductor Selection
The inductor is selected based on trade-off among size, cost, efficiency, and transient performance. A good starting point
for inductance comes from targeting 30% peak-to-peak ripple current to average current ratio. The switching frequency,
input voltage, output voltage, and target ripple are related to inductance as shown below:
(VIN − VOUT) × D
L= f
SW × IOUT × 30 %
where D (=VOUT/VIN) is the duty cycle. VIN, VOUT, and IOUT are typical values (so that efficiency is optimum for typical
conditions).
The inductance must satisfy the slope compensation criterion:
VOUT
VSLOPEfSW > 2 × L AVCSRCS
where AVCS is the current-sense amplifier gain (typical 13V/V). VSLOPE is VOUT dependent and is given by the following
equation:
www.maximintegrated.com
Maxim Integrated | 20
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
VSLOPE
= 105mV for 0V < VOUT ≤ 3V
= 210mV for 3V < VOUT ≤ 5.5V
= 420mV for 5.5V < VOUT ≤ 9.7V
= 525mV
otherwise
Peak Inductor Current
The peak inductor current is the sum of maximum load current and half of the peak-to-peak ripple current:
∆ IL
IPEAK = ILOAD(MAX) + 2
For the selected inductance value, the actual peak-to-peak inductor ripple current (ΔIL) is calculated using the following
equation:
∆ IL =
(
VOUT VIN − VOUT
VIN × fSW × L
)
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 peak current.
MOSFET Selection in Buck Converter
The high- and low-side n-channel MOSFETs should be selected to have sufficient voltage and current ratings. In addition,
they should be able to handle the heat generated and temperature rise.
Both high- and low-side MOSFETs should be rated for maximum input voltage observed in the application. Provide
additional margin for switch node ringing during switching.
Select MOSFETs with logic-level gate drive with guaranteed on-resistance specifications at VGS = 4.5V. If BIAS
switchover is enabled, the gate drive supply voltage follows VOUT. In those cases, select MOSFETs to have guaranteed
on-resistance at the lowest BIAS switchover voltage.
To reduce switching noise for smaller MOSFETs, use a series resistor in the BST path and additional gate capacitance.
Contact factory for guidance using gate resistors.
Current-Sense Measurement
For best current-sense accuracy and overcurrent protection, use a ±1% tolerance current-sense resistor between the
inductor and output, as shown in Figure 2 (A). This configuration continuously monitors inductor current, allowing
accurate current-limit protection. Use low-inductance current-sense resistors for accurate measurement.
Alternatively, high-power applications can reduce the overall power dissipation by connecting a DCR sensing network
across the inductor Figure 2 (B). Select DCR network based on the following equations:
(
R2
)
L
(
1
1
RCSHL = R + R RDCR and RDCR = C R + R
1
2
eq 1
2
)
where RCSHL is the required current-sense resistor based on the current-limit threshold (VLIMIT) and RDCR is the
inductor DC resistance. If DCR sense is the preferred current-sense method, select R1 ≤ 1kΩ. See Figure 2 (B).
Carefully observe the Layout Recommendations to ensure the noise and DC errors do not corrupt the differential currentsense signals seen by CS and OUT. Place the sense resistor close to the controller CS/OUT pins with short, direct traces,
making a Kelvin-sense connection to the current-sense resistor.
www.maximintegrated.com
Maxim Integrated | 21
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
INPUT (VIN)
CIN
MAX25206/7/8
DH
RCS
L
LX
COUT
DL
PGND
CS
OUT
(A) OUTPUT SERIES RESISTOR SENSING
INPUT (VIN)
CIN
MAX25206/7/8
INDUCTOR
DH
L
RDCR
LX
R1
DL
COUT
R2
Ceq
PGND
CS
OUT
(B) LOSSLESS INDUCTOR DCR SENSING
Figure 2. Current-Sense Configurations
Input Capacitor in Buck Converter
Select input capacitor to satisfy the following conditions
● Withstand input ripple current in buck power stage
● Limit the input voltage ripple
The RMS current in the input capacitor is given by:
ICIN.RMS = ILOAD(MAX)√D × (1 − D)
The input voltage ripple is composed of ΔVIN.C (caused by the capacitor discharge) and ΔVIN.ESR (caused by the ESR
of the input capacitor) given by:
ΔVIN.C =
ILOAD(MAX) x D(1 − D)
CIN x fSW
(
ΔIL
and ΔVIN.ESR = ESRCIN ILOAD(MAX) + 2
)
ILOAD(MAX) is the maximum output current, ΔIL is the peak-to-peak inductor current ripple, and CIN is the input capacitor.
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 voltages, additional input
capacitance helps avoid possible undershoot below the undervoltage lockout threshold during transient loading.
www.maximintegrated.com
Maxim Integrated | 22
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Output Capacitor in Buck Converter
The output capacitor is selected to meet ripple requirements, both in steady state and during transients. Low ESR
ceramic capacitors can be utilized.
The steady state output ripple has capacitive and ESR based components given by:
1
ΔIL
ΔVOUT.C = 8 f C
and ΔVOUT.ESR = ΔIL × ESRCOUT
sw OUT
When using low-capacity filter capacitors, such as ceramic capacitors, capacitor selection is usually driven by the need
to limit undershoot and overshoot during load transients. The design should be verified in the lab to ensure undershoot
and overshoot requirements are met.
Control Loop / Compensation
The IC uses a peak current-mode control scheme that regulates the output voltage by controlling the required current
through the external inductor. Current mode 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 required to have a stable, high-bandwidth loop in applications where
ceramic capacitors are used for output filtering (see Figure 3). For high-ESR (non-ceramic) output capacitors, the zero
created by the capacitance and ESR can be close to or lower than the desired closed-loop crossover frequency. To
stabilize a high-ESR (non ceramic) 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 3. The DC gain of the modulator is given by:
GAINMOD(DC) = gmc x RLOAD
where RLOAD = VOUT/ILOAD(MAX) in Ω and gmc = 1/(AVCS x RCS) in S. AVCS is the voltage gain of the current-sense
amplifier and is typically 13V/V. RCS is current-sense resistor in Ω. When using DCR sensing network, replace RCS with
RCSHL.
In a current-mode step-down converter, the output capacitor and the load resistance introduce a pole at the frequency:
1
fpMOD = 2π x C
OUT x RLOAD
The output capacitor and its ESR also introduce a zero given by:
1
fzMOD = 2π x ESR
COUT x COUT
When COUT is composed of “n” identical capacitors in parallel, the resulting COUT = n x COUT(EACH), and ESRCOUT
= ESRCOUT(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 0.7V (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 450µS (typ), and ROUT,EA is the output resistance of the error amplifier, which is
30MΩ (typ).
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 the compensation capacitor to cancel the output capacitor ESR zero if it occurs near the crossover frequency (fC,
where the loop gain equals 1 (0dB)).
fdpEA =
1
2π
x
(
CC x ROUT, EA + RC
1
)
1
fzEA = 2π x C x R fpEA = 2π x C x R
C
C
F
C
The loop-gain crossover frequency (fC) should be set below 1/5th of the switching frequency and much higher than the
www.maximintegrated.com
Maxim Integrated | 23
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
power-modulator pole (fpMOD). Select a value for fC in the range shown below:
fSW
fpMOD ≪ fC ≤ 5
At the crossover frequency, the total loop gain is unity. Select RC based on the target crossover frequency:
VOUT
2π
RC = f C × V
×g
× AVCSRCS × COUT
FB
m, EA
Set the error-amplifier compensation zero formed by RC and CC at fpMOD:
1
CC = 2π × f
pMOD × RC
If fzMOD is less than 5 x fC, add a second capacitor CF from COMP to AGND using the equation below:
1
CF = 2π × f
zMOD × RC
As the load current decreases, the modulator pole frequency also decreases; however, the modulator gain increases
accordingly and the crossover frequency remains the same.
gmc = 1/(AVCS x RCS)
CS
CURRENT-MODE
POWER
MODULATION
OUT
RFB2
ESRCOUT
gm,EA = 450µS
FB
COUT
COMP
ERROR
AMP
RRFB1
VREF
30MΩ
RC
CF
CC
Figure 3. Compensation Network
Layout Recommendations
PCB layout is critical for stable operation, low noise, and high efficiency. Use the checklist below to achieve good circuit
performance (See Figure 4 for an example):
● Place the input capacitor (CIN), the high-side MOSFET (QH), and the low-side MOSFET (QL) so that the "input loop"
area involving high di/dt is minimized.
● Use low-ESR/ESL ceramic capacitors (CIN) close to the input loop. Bulk capacitor can be further away.
● Place the output capacitors (COUT) so that input and output capacitor grounds are close together. In addition, connect
this common ground connection to ground plane layer(s) using multiple vias.
● Use short and wide traces/areas for high current paths (VIN, VOUT, LX, PGND). If possible, run them on multiple
layers in parallel to minimize resistance.
www.maximintegrated.com
Maxim Integrated | 24
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
● Minimize the area of high dv/dt nodes (LX) to the extent permitted by heating considerations.
● Route gate drive forward and return paths together using short and wide traces to minimize loop impedance.
Wherever possible, use traces wider than 25 mils for outer layers and 50 mils for inner layers.
● High-side gate charging path includes CBST. Place CBST as close to the IC pins (BST/LX) as possible.
● Low-side gate charging path includes CBIAS. Place CBIAS as close to the IC pins (BIAS/PGND) as possible.
● Low-side gate charge/discharge path includes PGND. Ensure that a continuous PGND plane is present under DL
path.
● Place the sense resistor (RCS) close to the CS/OUT pins. Use Kelvin connections across the sense resistor (RCS)
and route differentially to the IC pins (CS/ OUT). Make the sense traces as short as possible. Place a 22nF capacitor
near the CS/OUT pins to minimize noise due to sense trace inductance.
● Use AGND as the reference ground for sensitive analog signals (FB, COMP). Connect the ground side of the bottom
feedback resistor (RFB1) and compensation components (CC, CF) to AGND.
● Route sensitive traces (FB, CS/OUT) away from noisy (high dv/dt and di/dt) areas (BST, LX, DH, DL).
● Connect AGND/PGND under the IC at one point (Figure 4).
● Connect IC exposed pad through multiple vias to ground plane layer(s).
● Use thicker copper (preferably 2oz/ft2) for higher current designs for better efficiency and thermal performance.
SMALL
INPUT
LOOP
LOW SIDE
HIGH SIDE
MOSFET (QH) MOSFET (QL)
INDUCTOR
VIN
CIN CIN
AGND-PGND
CONNECTION
UNDER THE IC
GND
CBIAS
COUT
MAX25206/7/8
OUT/CS
DIFFERENTIAL
ROUTING
COUT
KELVIN-SENSE
VIAS UNDER THE
SENSE RESISTOR
(RCS)
VOUT
Figure 4. Layout Example
www.maximintegrated.com
Maxim Integrated | 25
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Typical Application Circuits
Application Circuit 1: 5VOUT 2.2MHz 7A
1.2µH
10mΩ
4.7µF
2x47µF
2.2µF
DL
LX
BST
ENBK
(MAX25207 ONLY)
SUP
47µF
DH
0.1µF
PGND
CS
EN
MAX25206/7/8
FSYNC
OUT
FB
SYNCOUT
BIAS
FOSC
COMP
PGOOD
BIAS
AGND
12kΩ
10kΩ
2.2µF
100kΩ
1500pF
www.maximintegrated.com
Maxim Integrated | 26
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Typical Application Circuits (continued)
Application Circuit 2: 16VOUT 440kHz 7A
10µH
10mΩ
4.7µF
2x47µF
DL
LX
BST
ENBK
(MAX25207 ONLY)
SUP
47µF
DH
0.1µF
PGND
2.2µF
CS
EN
MAX25206/7/8
FSYNC
OUT
FB
SYNCOUT
FOSC
10kΩ
COMP
PGOOD
BIAS
AGND
66.5kΩ
220kΩ
10kΩ
2.2µF
120kΩ
1500pF
www.maximintegrated.com
Maxim Integrated | 27
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Typical Application Circuits (continued)
Application Circuit 3: 12VOUT 2.2MHz 7A
2.2µH
10mΩ
4.7µF
2x47µF
2.2µF
DL
LX
BST
ENBK
(MAX25207 ONLY)
SUP
47µF
DH
0.1µF
PGND
CS
EN
MAX25206/7/8
FSYNC
OUT
FB
SYNCOUT
FOSC
10kΩ
COMP
PGOOD
BIAS
AGND
12kΩ
162kΩ
10kΩ
2.2µF
165kΩ
1500pF
www.maximintegrated.com
Maxim Integrated | 28
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Ordering Information
PART
VOUT
ADJUSTABLE
FIXED
SWITCHOVER IN FPWM
BYPASS VOLTAGE
MAX25206ATPA/VY+
0.7V TO 20V
5V
ON
–
MAX25206ATPB/VY+*
0.7V TO 20V
3.3V
ON
–
MAX25207ATPA/VY+
0.7V TO 20V
5V
OFF
14V
MAX25208ATPA/VY+*
0.7V TO 20V
5V
ON
–
+ Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes automotive qualified
Y Denotes wettable flank
*Future product—contact factory for availability
Contact factory for switchover disabled
www.maximintegrated.com
Maxim Integrated | 29
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA IQ and Optional Bypass Mode
Revision History
REVISION
NUMBER
REVISION
DATE
0
8/20
DESCRIPTION
Initial release
PAGES
CHANGED
—
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.
© 2020 Maxim Integrated Products, Inc.
工商网监
湘ICP备2023018690号
