MAX25206 [MAXIM]
Versatile Automotive 60V/70V 2.2MHz Buck Controller with 7μA IQ and Optional Bypass Mode;
| 型号： | MAX25206 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Versatile Automotive 60V/70V 2.2MHz Buck Controller with 7μA IQ and Optional Bypass Mode |
| 文件： | 总30页 (文件大小：1108K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass
Q
Mode
General Description
Benefits and Features
The MAX25206/MAX25207/MAX25208 are automotive
● 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
2.2MHz synchronous step-down controllers with 7μA I .
Q
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 in-
tended for applications with mid- to high-power require-
ments that operate at a wide input voltage range such
as during automotive cold-crank or engine stop-start con-
ditions. The MAX25207 has an optional bypass mode,
which allows 100% high-side switch on until step-down
function is needed during automotive transients.
● 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
The MAX25206/MAX25207/MAX25208 step-down con-
trollers operate at a frequency up to 2.2MHz to allow small
external components, reduced output ripple, and to elim-
inate AM band interference. The switching frequency is
resistor adjustable (220 kHz to 2200 kHz). SYNC input
programmability enables three frequency modes for opti-
mized performance: forced fixed-frequency operation (FP-
WM), skip mode with ultra-low quiescent current, and syn-
chronization 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 mod-
ulation to minimize EMI.
• 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
The MAX25206/MAX25207/MAX25208 feature a PGOOD
monitor and undervoltage lockout. Protection features in-
clude cycle-by-cycle current limit and thermal shutdown.
These controllers are specified for operation over the
-40°C to +125°C automotive temperature range.
● 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
Applications
● Infotainment Systems
● 48V Systems
● General Purpose Point of Load (POL)
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 I and Optional Bypass Mode
Q
Simplified Block Diagram
V
OUT
-OR-
L
R
CS
V
– I*(R +R +R )
DS DCR CS
BAT
V
BAT
C
OUT
C
BST
PGND
SUP
C
IN
CS
EN
OUT
MAX25206/7/8
FSYNC
FB
SYNCOUT
FOSC
R
FOSC
R
C
C
BIAS
C
F
C
C
www.maximintegrated.com
Maxim Integrated | 2
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
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 I and Optional Bypass Mode
Q
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: 5V
2.2MHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
OUT
Application Circuit 2: 16V
Application Circuit 3: 12V
440kHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2MHz 7A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
OUT
OUT
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 I and Optional Bypass Mode
Q
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 I and Optional Bypass Mode
Q
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, V
, rising must cross 6V. The normal operating range is then valid.
SUP
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
TYPICAL
RANGE
PARAMETER
SYMBOL
CONDITION
UNIT
-40 to
+125
Ambient Temperature Range
ºC
Note: These limits are not guaranteed.
Package Information
20 SW TQFN
Package Code
T2044Y+6C
21-100388
90-100132
Outline Number
Land Pattern Number
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θ
)
35.4 ºC/W
4 ºC/W
JA
Junction to Case (θ
)
JC
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
(V
= 24V (MAX25206, MAX25207)/48V (MAX25208), V
= V
, C
SUP SUP
= 4.7μF, C
= 2.2μF, C
= 0.1μF, R
= 12kΩ,
FOSC
SUP
EN
BIAS
BST
T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C. (Note 2 and 5))
J
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SYNCHRONOUS STEP DOWN CONVERTER
Normal Operation (MAX25206 and
MAX25207) (Note 3)
3.5
3.5
60
70
Supply Voltage Range
V
SUP
V
Normal Operation (MAX25208) (Note 3)
www.maximintegrated.com
Maxim Integrated | 6
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Electrical Characteristics (continued)
(V
= 24V (MAX25206, MAX25207)/48V (MAX25208), V
= V
, C
SUP SUP
= 4.7μF, C
= 2.2μF, C
= 0.1μF, R
= 12kΩ,
FOSC
SUP
EN
BIAS
BST
T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C. (Note 2 and 5))
J
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
107
105
1
MAX
UNITS
Detected with respect to V Rising
Output Overvoltage
Threshold
FB
%
Detected with respect to V Falling
FB
V
V
= 0V
6
EN
µA
= V
, V
= 5V, No Switching,
EN
SUP OUT
7
3
11
Supply Current
I
MAX25206/8
SUP
V
EN
= V
= 14V, MAX25207 in bypass
SUP
mA
mode
V
FB
V
FB
V
FB
V
FB
= V
= V
= V
= V
, V
= 5V, PWM mode
, V = 5V, skip mode
BIAS OUT
4.925
4.9
5
5.075
5.1
BIAS OUT
5
Buck Fixed Output
Voltage
V
OUT
V
, V
= 3.3V, PWM mode
= 3.3V, skip mode
3.234
3.234
3.3
3.3
3.366
3.366
BIAS OUT
, V
BIAS OUT
Output Voltage
Adjustable Range
Buck
0.7
20
0.715
1
V
V
Regulated Feedback
Voltage
V
0.689
0.7
0.01
0.01
450
FB
Feedback Leakage
Current
I
T
A
= +25°C
µA
%/V
µS
FB
Feedback Line
Regulation Error
V
V
= 3.5V to 60V, V = 0.7V
FB
SUP
Transconductance (from
FB to COMP)
g
= 0.7V, V = 5V
BIAS
220
97
650
m, EA
FB
DL low to DH Rising
DH low to DL Rising
Buck
15
15
Dead Time
ns
Max Duty Cycle
%
Minimum On-Time
t
Buck
50
ns
ON,MIN
PWM Switching
Frequency Range
f
Programmable
0.22
2
2.2
2.4
89
MHz
MHz
mV
SW
Switching Frequency
Accuracy
R
FOSC
= 12kΩ, V
= 5V, 3.3V
BIAS
2.2
80
CS Current-Limit
Voltage Threshold
V
V
CS
– V
; V
= 5V, V ≥ 2.5V
OUT
71
LIMIT
OUT BIAS
Buck, fixed soft-start time regardless of
frequency.
Soft-Start Ramp Time
t
3.7
ms
SOFT-START
V
25°C
= 6V, V = V
or V
, T =
SUP A
SUP
LX
PGND
LX Leakage Current
DH Pullup Resistance
0.01
2.7
1
µA
Ω
V
= 5V, I
= 5V, I
= -100mA
= 100mA
BIAS
BIAS
DH
DH
DH Pulldown
Resistance
V
Ω
DL Pullup Resistance
V
V
= 5V, I = -100mA
2.2
1
Ω
Ω
BIAS
DL
DL Pulldown Resistance
= 5V, I = 100mA
DL
BIAS
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Maxim Integrated | 7
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Electrical Characteristics (continued)
(V
= 24V (MAX25206, MAX25207)/48V (MAX25208), V
= V
, C
SUP SUP
= 4.7μF, C
= 2.2μF, C
= 0.1μF, R
= 12kΩ,
FOSC
SUP
EN
BIAS
BST
T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C. (Note 2 and 5))
J
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
95
MAX
UNITS
P
% of target V
% of target V
, Rising
, Falling
GOOD_H
OUT
OUT
PGOOD UV Threshold
%
P
90.5
93
95.5
1
GOOD_F
PGOOD Leakage
Current
V
= 5V, T = 25°C
0.01
µA
V
PGOOD
A
PGOOD Output Low
Voltage
I
= 1mA
0.2
SINK
PGOOD Debounce
Time
OV/UV Fault Detection, Rising and
Falling
32
µs
PGOOD Timeout
OTP Option (default 0ms) rising
0.5
-3
ms
Bypass Mode
Rising threshold where buck starts (14V
to 18V, 0.5V Steps) MAX25207
Bypass Mode Threshold
V
BYP
3
%
Hysteresis
0.7
V
V
ENBK Threshold, High
ENBK Threshold, Low
ENBK Internal Pulldown
FSYNC INPUT
V
1.4
IH
V
0.4
V
IL
620
kΩ
f
= 2.2MHz, minimum sync pulse >
OSC
1.8
2.6
MHz
kHz
(1/f
- 1/f
)
OSC
SYNC
FSYNC Frequency
Range
f
= 400kHz, minimum sync pulse >
OSC
320
100
1.4
480
(1/f
- 1/f
)
OSC
SYNC
Minimum sync-in pulse
ns
V
High Threshold
FSYNC Switching
Thresholds
Low Threshold
0.4
3.5
V
INTERNAL LDO BIAS
Internal BIAS Voltage
V
SUP
V
BIAS
V
BIAS
> 6V
5
V
V
Rising
Falling
3.1
2.8
BIAS UVLO Threshold
2.6
THERMAL OVERLOAD
Thermal Shutdown
Temperature
T rising (Note 4)
J
165
20
°C
°C
Thermal Shutdown
Hysteresis
(Note 4)
Logic Levels
EN High Threshold
EN Low Threshold
EN Input Bias Current
SPS Threshold, High
SPS Threshold, Low
EN
EN
1.4
1.4
V
V
0.4
1
EN logic input only, T = 25°C
0.01
μA
V
A
V
IH,SPS
V
0.4
V
IL,SPS
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Maxim Integrated | 8
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Electrical Characteristics (continued)
(V
= 24V (MAX25206, MAX25207)/48V (MAX25208), V
= V
, C
SUP SUP
= 4.7μF, C
= 2.2μF, C
= 0.1μF, R
= 12kΩ,
FOSC
SUP
EN
BIAS
BST
T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C. (Note 2 and 5))
J
A
PARAMETER
SPS Internal Pulldown
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
620
kΩ
SYNCOUT and Spread Spectrum Logic
SYNCOUT Low Voltage
I
= 5mA
0.4
1
V
SINK
SYNCOUT Leakage
Current
T
= 25°C
µA
A
% of
Spread Spectrum
±6
f
OSC
o
Note 2: Limits are 100% production tested at T = +25 C. Limits over the operating temperature range and relevant supply voltage
A
are guaranteed by design and characterization.
Note 3: During initial startup, V
, rising must cross 6V. The normal operating range is then valid.
SUP
Note 4: Guaranteed by design; not production tested.
Note 5: The device is designed for continuous operation up to T = +125°C for 95,000 hours and T = +150°C for 5,000 hours.
J
J
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Maxim Integrated | 9
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Typical Operating Characteristics
www.maximintegrated.com
Maxim Integrated | 10
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Typical Operating Characteristics (continued)
www.maximintegrated.com
Maxim Integrated | 11
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Pin Configurations
MAX25206/MAX25208
TOP VIEW
15
14
13
12
11
LX 16
10
9
CS
17
18
19
20
OUT
FB
DH
MAX25206/8
8
BST
SUP
7
AGND
COMP
+
6
EN
1
2
3
4
5
TQFN
4mm × 4mm
MAX25207
TOP VIEW
15
14
13
12
11
LX 16
10
9
CS
17
18
19
20
OUT
FB
DH
MAX25207
8
BST
SUP
7
AGND
COMP
+
6
EN
1
2
3
4
5
TQFN
4mm × 4mm
Pin Description
PIN
NAME
FUNCTION
MAX25206/
MAX25208
MAX25207
Spread Spectrum Enable Pin. Pull to logic high for spread spectrum enabled. Pull
to ground to disable spread spectrum.
1
1
SPS
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Maxim Integrated | 12
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Pin Description (continued)
PIN
NAME
FUNCTION
MAX25206/
MAX25208
MAX25207
Clock Output. SYNCOUT outputs 180 degrees out of phase relative to the internal
oscillator.
2
3
4
5
2
SYNCOUT
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
4
5
FSYNC
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.
PGOOD
Buck Controller Error Amplifier Output. Connect an RC network between COMP
and AGND to compensate the buck controller.
6
7
6
7
COMP
AGND
Analog Ground for Controller
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).
8
8
FB
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 current-
sense element. See Current Limiting and Current Sense Inputs and Current Sense
Measurement sections.
9
9
OUT
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.
10
11
12
10
11
12
CS
NC
No Connect
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.
NC/ENBK
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
15
16
17
14
15
16
17
PGND
DL
Power Ground for Controller
Low-Side Gate Driver Output. DL output voltage swings from V
to V
BIAS.
PGND
LX
Inductor Connection. Connect LX to the switched side of the inductor.
High-Side Gate Driver Output
DH
Bootstrap capacitor connection. Connect a ceramic capacitor between BST and
LX. See High-Side Gate-Driver Supply (BST) section.
18
18
BST
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Maxim Integrated | 13
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Pin Description (continued)
PIN
NAME
FUNCTION
MAX25206/
MAX25208
MAX25207
Supply Input for IC. Bypass to ground with a 2.2μF or larger capacitor near the IC.
19
20
19
20
SUP
EN
Connect to buck power stage input voltage (V ). Power stage needs additional
input capacitors (C ).
IN
IN
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.
EP
EP
–
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Maxim Integrated | 14
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Functional Diagrams
Block Diagram
PGOOD
COMP
ENBK
SUP
OV
UV
BIAS
FB
CHARGE
PUMP
FEEDBACK
SELECT
E
AMP
-
+
+
SOFT
BST
START
REF = 0.7V
PWM
COMP
GATE DRIVE &
LOGIC
DH
LX
OUT
PWM
80mV (typ)
CSA
CS
EN
DL
ILIM
COMP
ILIM
PGND
LX
SLOPE
COMP
ZERO
CROSS
FSYNC
SELECT
LOGIC
FSYNC
SUP
OUT
BIAS
INTERNAL LDO
/SWITCHOVER
FOSC
SPS
CLK
OSCILLATOR
SYNCOUT
AGND
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Maxim Integrated | 15
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
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 V
, or to a power-supply sequencing logic.
SUP
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:
I
= I + f
× (QG + QG ) = 20mA to 50mA (typ) for 400kHz
BIAS
CC
SW DH DL
where I
is the internal supply current (3mA, typ), f
is the switching frequency. QG
is the gate charge of the upper
DH
CC
SW
MOSFET, and QG is the gate charge of the lower MOSFET. The BIAS linear regulator is not intended for powering
DL
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 (V
< V
- 0.7V). In this mode, the IC
SUP
BYP
utilizes an internal charge pump to maintain 100% duty cycle on the high-side MOSFET. When V
> V
, the IC
BYP
SUP
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 V
when driven high. See Bypass Timing Diagram for valid states and corresponding output.
SUP
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Maxim Integrated | 16
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Bypass Timing Diagram
1
0
V
ENBK
V
BYP
V
SUP
V
≈ V
SUP
OUT
V
= INTERNALLY PROGRAMMED OR SET
OUT
USING EXTERNAL RESISTOR DIVIDER
V
OUT
BYPASS
BUCK
BYPASS
BUCK
Figure 1. Bypass Timing
V
V
: Bypass voltage threshold. This is an OTP programmable threshold for bypass decision making in MAX25207.
BYP
: Output voltage. Buck mode output voltage is internally programmed or set using external resistor divider. Bypass
OUT
mode output voltage is approximately equal to the supply voltage.
V
ENBK
: Enable Buck. A logic high at ENBK pin forces buck mode regardless of V
.
SUP
Soft-Start
The soft-start circuitry gradually ramps up the reference voltage during soft-start time (t
) to reduce the input
SOFT-START
inrush current during startup. Before the device can begin soft-start, the following conditions must be met:
● V
● V
exceeds the BIAS UVLO threshold
is logic high
BIAS
EN
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 (R
) from FOSC to AGND:
FOSC
400kHz × 66kΩ
R
=
1 + 60ns × (2.2MHz − f
[
)
OSC
]
FOSC
f
OSC
where f
is in Hz and R
is in Ω.
FOSC
OSC
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
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Maxim Integrated | 17
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
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:
V
+ I
R
+ R
(
)
OUT OUT DS(ON)
DCR
V
≈
IN
0.97
where R
is the on-resistance of the high-side MOSFET.
DS(ON)
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
V
OUT
. 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 (C
) connected between BST and LX pins.
BST
C
re-charges from BIAS, through an internal switch, when the low-side MOSFET is on bringing LX to ground. For
BST
MAX25207 in bypass mode, C
is kept charged using an internal charge pump.
BST
The bootstrap capacitance (C
given by:
) is selected to limit the voltage drop on C
during high-side MOSFET turn on, as
BST
BST
C
= QG ∆ V
BST
/
BST
where QG is the total gate charge of the high-side MOSFET and ∆V
(100mV to 300mV) is the voltage ripple on C
.
BST
BST
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 I and Optional Bypass Mode
Q
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 (V
= 80mV (typ)), the PWM controller turns off the high-side MOSFET. The maximum
LIMIT
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 (V /V ).
OUT IN
For accurate current sensing, use a current-sense shunt resistor (R ) between the inductor and the output capacitor.
CS
Connect CS to the inductor side of R
and OUT to the output capacitor side. Select R
such that
CS
CS
ΔI
V
L
LIMIT
I
+
<
LOAD
2 R
CS
where ΔI is the inductor current ripple.
L
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 (V
= 80mV (typ)), the high-side driver (DH)
LIMIT
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 V
for MAX25206/
OUT
MAX25208, 20% of target V
for MAX25207).
OUT
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.
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Maxim Integrated | 19
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
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 (t
):
ON,MIN
V
OUT
> t
× f
SW
ON, MIN
V
IN
where f
is the switching frequency. If the desired voltage conversion does not meet the above condition, pulse skipping
SW
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 (f ) to
SW
~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.
R
R
V
FB2
FB1
OUT
=
− 1
V
(
)
FB
where V = 0.7V (typ) (see the Electrical Characteristics) and R
, R
FB2 FB1
are top and bottom resistors in the feedback
FB
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:
V
− V
× D
(
)
IN
× I
OUT
L =
f
× 30 %
SW OUT
where D (=V
conditions).
/V ) is the duty cycle. V , V
, and I are typical values (so that efficiency is optimum for typical
OUT
OUT IN
IN OUT
The inductance must satisfy the slope compensation criterion:
V
OUT
V
f
>
A
R
SLOPE SW
VCS CS
2 × L
where A
is the current-sense amplifier gain (typical 13V/V). V
is V dependent and is given by the following
OUT
VCS
SLOPE
equation:
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Maxim Integrated | 20
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
V
= 105mV for 0V < V
= 210mV for 3V < V
≤ 3V
SLOPE
OUT
OUT
≤ 5.5V
= 420mV for 5.5V < V
≤ 9.7V
OUT
= 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:
∆ I
L
I
= I
+
LOAD(MAX)
2
PEAK
For the selected inductance value, the actual peak-to-peak inductor ripple current (ΔI ) is calculated using the following
L
equation:
V
V
− V
(
)
OUT IN
OUT
× L
∆ I =
L
V
× f
IN SW
The saturation current should be larger than I
or at least in a range where the inductance does not degrade
PEAK
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 V
= 4.5V. If BIAS
GS
switchover is enabled, the gate drive supply voltage follows V
on-resistance at the lowest BIAS switchover voltage.
. In those cases, select MOSFETs to have guaranteed
OUT
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:
R
2
L
1
1
R
=
R
and R =
DCR
+
R R
CSHL
DCR
R + R
C
(
)
(
)
1
2
eq
1
2
where R
is the required current-sense resistor based on the current-limit threshold (V
) and R
is the
DCR
CSHL
LIMIT
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 current-
sense 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.
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Maxim Integrated | 21
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
INPUT (V
)
IN
C
IN
L
MAX25206/7/8
DH
R
CS
LX
DL
C
OUT
PGND
CS
OUT
(A) OUTPUT SERIES RESISTOR SENSING
INPUT (V
)
IN
C
IN
MAX25206/7/8
INDUCTOR
DH
LX
L
R
DCR
C
OUT
R1
R2
DL
C
eq
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:
I
= I
D × (1 − D)
√
LOAD(MAX)
CIN.RMS
The input voltage ripple is composed of ΔV
of the input capacitor) given by:
(caused by the capacitor discharge) and ΔV
(caused by the ESR
IN.ESR
IN.C
I
x D(1 − D)
ΔI
LOAD(MAX)
L
ꢀ ΔV
=
and ΔV
= ESR
I
+
IN.C
IN.ESR
CIN LOAD(MAX)
(
C
x f
2
)
IN
SW
I
is the maximum output current, ΔI is the peak-to-peak inductor current ripple, and C is the input capacitor.
LOAD(MAX)
L
IN
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.
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Maxim Integrated | 22
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
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:
ΔI
1
L
ΔV
=
and ΔV
= ΔI × ESR
OUT.ESR L COUT
OUT.C
8 f
C
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 (R ) and capacitor (C ) is required to have a stable, high-bandwidth loop in applications where
C
C
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 (C ) from COMP to AGND
F
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:
GAIN
= g
x R
mc LOAD
MOD(DC)
where R
= V
/I
in Ω and g
= 1/(A
x R ) in S. A
is the voltage gain of the current-sense
VCS
LOAD
OUT LOAD(MAX)
mc
VCS
CS
amplifier and is typically 13V/V. R
is current-sense resistor in Ω. When using DCR sensing network, replace R
with
CS
CS
R
.
CSHL
In a current-mode step-down converter, the output capacitor and the load resistance introduce a pole at the frequency:
1
f
=
pMOD
2π x C
x R
OUT
LOAD
The output capacitor and its ESR also introduce a zero given by:
1
f
=
2π x ESR
zMOD
x C
COUT
OUT
When C
is composed of “n” identical capacitors in parallel, the resulting C
= n x C
, and ESR
OUT(EACH) COUT
OUT
OUT
= ESR
/n. Note that the capacitor zero for a parallel combination of alike capacitors is the same as for an
COUT(EACH)
individual capacitor.
The feedback voltage-divider has a gain of GAIN = V /V
, where V is 0.7V (typ).
FB
FB
FB OUT
The transconductance error amplifier has a DC gain of GAIN
= g
x R
, where g
is the error
m,EA
EA(DC)
m,EA
OUT,EA
amplifier transconductance, which is 450µS (typ), and R
30MΩ (typ).
is the output resistance of the error amplifier, which is
OUT,EA
A dominant pole (f
) is set by the compensation capacitor (C ) and the amplifier output resistance (R
). A zero
OUT,EA
dpEA
C
(f
) is set by the compensation resistor (R ) and the compensation capacitor (C ). There is an optional pole (f
)
zEA
C
C
pEA
set by the compensation capacitor to cancel the output capacitor ESR zero if it occurs near the crossover frequency (f ,
C
where the loop gain equals 1 (0dB)).
1
1
1
f
=
ꢀ ꢀ f
=
ꢀ ꢀ f
=
dpEA
zEA
pEA
2π x C x R
2π x C x R
C
C
F
C
2π
x
C
x
R
+ R
(
)
C
C
OUT, EA
The loop-gain crossover frequency (f ) should be set below 1/5th of the switching frequency and much higher than the
C
www.maximintegrated.com
Maxim Integrated | 23
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
power-modulator pole (f
). Select a value for f in the range shown below:
pMOD
C
f
SW
5
f
≪ f ≤
pMOD
C
At the crossover frequency, the total loop gain is unity. Select R based on the target crossover frequency:
C
V
OUT
2π
R = f ×
×
× A
R
× C
C
C
VCS CS OUT
V
g
FB
m, EA
Set the error-amplifier compensation zero formed by R and C at f
:
C
C
pMOD
1
C =
C
2π × f
× R
pMOD
C
If f
is less than 5 x f , add a second capacitor C from COMP to AGND using the equation below:
zMOD
C
F
1
C =
F
2π × f
× R
zMOD
C
As the load current decreases, the modulator pole frequency also decreases; however, the modulator gain increases
accordingly and the crossover frequency remains the same.
g
= 1/(A
x R
CS
)
mc
VCS
CS
CURRENT-MODE
POWER
OUT
MODULATION
R
FB2
g
= 450µS
m,EA
ESR
C
COUT
FB
COMP
ERROR
AMP
R
RFB1
OUT
V
REF
30MΩ
R
C
C
F
C
C
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 (C ), the high-side MOSFET (QH), and the low-side MOSFET (QL) so that the "input loop"
IN
area involving high di/dt is minimized.
● Use low-ESR/ESL ceramic capacitors (C ) close to the input loop. Bulk capacitor can be further away.
IN
● Place the output capacitors (C
) so that input and output capacitor grounds are close together. In addition, connect
OUT
this common ground connection to ground plane layer(s) using multiple vias.
● Use short and wide traces/areas for high current paths (V , V
, LX, PGND). If possible, run them on multiple
IN OUT
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 I and Optional Bypass Mode
Q
● 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 C
. Place C
. Place C
as close to the IC pins (BST/LX) as possible.
BST
BST
● Low-side gate charging path includes C
as close to the IC pins (BIAS/PGND) as possible.
BIAS
BIAS
● Low-side gate charge/discharge path includes PGND. Ensure that a continuous PGND plane is present under DL
path.
● Place the sense resistor (R ) close to the CS/OUT pins. Use Kelvin connections across the sense resistor (R
)
CS
CS
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 (R
) and compensation components (C , C ) to AGND.
FB1
C F
● 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).
2
● Use thicker copper (preferably 2oz/ft ) for higher current designs for better efficiency and thermal performance.
SMALL
INPUT
LOOP
LOW SIDE
HIGH SIDE
MOSFET (QL) INDUCTOR
MOSFET (QH)
V
IN
C
C
IN
IN
GND
AGND-PGND
CONNECTION
UNDER THE IC
C
BIAS
KELVIN-SENSE
VIAS UNDER THE
SENSE RESISTOR
C
C
OUT
OUT
MAX25206/7/8
(R
)
CS
OUT/CS
DIFFERENTIAL
ROUTING
V
OUT
Figure 4. Layout Example
www.maximintegrated.com
Maxim Integrated | 25
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Typical Application Circuits
Application Circuit 1: 5V
2.2MHz 7A
OUT
1.2µH
10mΩ
4.7µF
2x47µF
0.1µF
PGND
SUP
2.2µF
47µF
CS
EN
OUT
MAX25206/7/8
FSYNC
FB
BIAS
SYNCOUT
FOSC
12kΩ
10kΩ
100kΩ
1500pF
2.2µF
www.maximintegrated.com
Maxim Integrated | 26
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Typical Application Circuits (continued)
Application Circuit 2: 16V
440kHz 7A
OUT
10µH
10mΩ
4.7µF
2x47µF
0.1µF
PGND
SUP
EN
47µF
2.2µF
CS
OUT
MAX25206/7/8
220kΩ
FSYNC
FB
SYNCOUT
FOSC
10kΩ
66.5kΩ
10kΩ
120kΩ
1500pF
2.2µF
www.maximintegrated.com
Maxim Integrated | 27
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Typical Application Circuits (continued)
Application Circuit 3: 12V
2.2MHz 7A
OUT
2.2µH
10mΩ
4.7µF
2x47µF
0.1µF
PGND
SUP
EN
2.2µF
47µF
CS
OUT
MAX25206/7/8
162kΩ
FSYNC
FB
SYNCOUT
FOSC
10kΩ
12kΩ
10kΩ
165kΩ
2.2µF
1500pF
www.maximintegrated.com
Maxim Integrated | 28
MAX25206/MAX25207/
MAX25208
Versatile Automotive 60V/70V 2.2MHz Buck
Controller with 7µA I and Optional Bypass Mode
Q
Ordering Information
V
OUT
PART
SWITCHOVER IN FPWM
BYPASS VOLTAGE
ADJUSTABLE
0.7V TO 20V
0.7V TO 20V
0.7V TO 20V
0.7V TO 20V
FIXED
5V
MAX25206ATPA/VY+
MAX25206ATPB/VY+*
MAX25207ATPA/VY+
MAX25208ATPA/VY+*
ON
ON
–
–
3.3V
5V
OFF
ON
14V
–
5V
+ 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 I and Optional Bypass Mode
Q
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
0
8/20
Initial release
—
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.
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