19-5673; Rev 0; 3/11
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
General Description
The MAX16975 is a 1.2A current-mode step-down con-
verter with an integrated high-side switch. The device
operates with input voltages from 3.5V to 28V while using
only 45FA quiescent current at no load. The switching
frequency is adjustable from 220kHz to 1.0MHz by using
an external resistor, and can be synchronized to an exter-
nal clock. The device’s output voltage is pin-selectable to
a fixed 5V or adjustable from 1V to 10V using external
resistors. The wide input voltage range makes the device
ideal for automotive and industrial applications.
The device operates in skip mode for reduced current
consumption in light-load conditions. An adjustable
reset threshold helps keep microcontrollers alive down
to the lowest specified input voltage. Protection features
include cycle-by-cycle current limit, soft-start, overvolt-
age, and thermal shutdown with automatic recovery.
The device also features a power-good monitor to ease
power-supply sequencing.
The device operates over the -40°C to +125°C automo-
tive temperature range, and is available in 16-pin QSOP
and QSOP-EP packages.
Ordering Information
appears at end of data sheet.
Features
S
Wide 3.5V to 28V Input Voltage Range
S
42V Input Transient Tolerance
S
5V Fixed or 1V to 10V Adjustable Output Voltage
S
Integrated 1.2A High-Side Switch
S
220kHz to 1.0MHz Adjustable Switching Frequency
S
Frequency Synchronization Input
S
Internal Boost Diode
S
45µA Skip-Mode Operating Current
S
Less than 10µA Shutdown Current
S
Adjustable Power-Good Output Level and Timing
S
3.3V Logic Level to 42V Compatible Enable Input
S
Current-Limit, Thermal Shutdown, and
Overvoltage Protection
S
-40°C to +125°C Automotive Temperature Range
Applications
Automotive
Industrial
Typical Application Circuit
3.5V TO 28V
C
IN1
47µF
C
IN2
4.7µF
C
IN3
0.1µF
SUP
EN
FSYNC
C
COMP1
5600pF
R
COMP
12kI
COMP
C
COMP2
OPEN
R
FOSC
61.9kI
FOSC
SUPSW
BST
LX
OUT
C
BST
0.1µF
L1
10µH
R
FB1
25kI
V
OUT
= 1.25V AT
1.2A AT 400kHz
C
OUT1
47µF
C
OUT2
47µF
V
OUT
D1
MAX16975
RESETI
V
BIAS
FB
R
RES
10kI
R
FB2
100kI
C
BIAS
1µF
BIAS
C
CRES
1nF
CRES
GND
RES
PLACE C
IN3
(0.1µF) RIGHT NEXT TO SUP.
For related parts and recommended products to use with this part, refer to:
www.maxim-ic.com/MAX16975.related
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Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
ABSOLUTE MAXIMUM RATINGS
SUP, SUPSW, LX, EN to GND ...............................-0.3V to +45V
BST to GND ..........................................................-0.3V to +47V
BST to LX ...............................................................-0.3V to +6V
OUT to GND ..........................................................-0.3V to +12V
SUP to SUPSW .....................................................-0.3V to +0.3V
RESETI, FOSC, COMP, BIAS,
FSYNC, CRES,
RES,
FB to GND .........................-0.3V to +6V
Output Short-Circuit Duration ....................................Continuous
Continuous Power Dissipation (T
A
= +70NC)
QSOP (derate 9.6 mW/NC above +70NC) .................771.5mW
Operating Temperature Range ........................ -40NC to +125NC
Junction Temperature .....................................................+150NC
Storage Temperature Range............................ -65NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
PACKAGE THERMAL CHARACTERISTICS (Note 1)
QSOP
Junction-to-Ambient Thermal Resistance (q
JA
) .....103.7°C/W
Note 1:
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to
www.maxim-ic.com/thermal-tutorial.
ELECTRICAL CHARACTERISTICS
(V
SUP
= V
SUPSW
= 14V, V
EN
= 14V, L1 = 22FH, C
IN
= 4.7FF, C
OUT
= 100FF, C
BIAS
= 1FF, C
BST
= 0.1FF, C
CRES
= 1nF, R
FOSC
=
61.9kI, T
A
= T
J
= -40NC to +125NC, unless otherwise noted. Typical values are at T
A
= +25NC.)
PARAMETER
Supply Voltage
Supply Current
Shutdown Supply Current
BIAS Regulator Voltage
BIAS Undervoltage Lockout
BIAS Undervoltage Hysteresis
Thermal-Shutdown Threshold
Thermal-Shutdown Threshold
Hysteresis
OUTPUT VOLTAGE (OUT)
Normal operation, V
FB
= V
BIAS
, I
LOAD
= 1A,
T
A
= +25°C
Normal operation, V
FB
= V
BIAS
, I
LOAD
= 1A,
-40°C
P
T
A
P
+125°C
V
OUT
= 5V, V
FB
= V
BIAS,
30mA < I
LOAD
< 1A
6V < V
SUP
< 28V
4.95
4.9
4.9
5
5
5.05
0.3
0.02
5.05
V
5.1
5.2
V
%
%/V
V
BIAS
V
UVBIAS
SYMBOL
V
SUP
,
V
SUPSW
I
SUP
CONDITIONS
Normal operation
Normal operation, no switching
Skip mode, no load, V
OUT
= 5V
V
EN
= 0V
V
SUP
= V
SUPSW
= 6V to 42V, V
OUT
< 3V or
V
OUT
> 5.5V, I
LOAD
= 0A (Note 2)
V
BIAS
rising
4.7
2.95
MIN
3.5
2.9
45
9
5.0
3.15
550
+175
+15
5.3
3.35
TYP
MAX
28
UNITS
V
mA
FA
FA
V
V
mV
NC
NC
Output Voltage
V
OUT
Skip-Mode Output Voltage
Load Regulation
Line Regulation
V
OUT_SKIP
No load, V
FB
= V
BIAS
(Note 3)
½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½
Maxim Integrated Products
2
*The
parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
ELECTRICAL CHARACTERISTICS* (continued)
(V
SUP
= V
SUPSW
= 14V, V
EN
= 14V, L1 = 22FH, C
IN
= 4.7FF, C
OUT
= 100FF, C
BIAS
= 1FF, C
BST
= 0.1FF, C
CRES
= 1nF, R
FOSC
=
61.9kI, T
A
= T
J
= -40NC to +125NC, unless otherwise noted. Typical values are at T
A
= +25NC.)
PARAMETER
BST Input Current
LX Current Limit
Skip-Mode Current Threshold
Power-Switch On-Resistance
LX Leakage Current
FB Input Current
SYMBOL
I
BST
I
LX
I
SKIP_TH
R
ON
I
LX,LEAK
I
FB
V
FB
FB connected to an external resistive divider,
T
A
= +25°C
FB connected to an external resistive divider,
-40°C
P
T
A
P
+125°C
4.5V < V
SUP
< 28V
V
FB
= 1V, V
BIAS
= 5V
0.99
0.985
R
ON
measured between SUPSW and LX, I
LX
=
1A, V
SUP
= 4.5V to 28V, V
BST
- V
LX
= 4.5V
V
SUPSW
= 28V, V
LX
= 0V, T
A
= +25°C
CONDITIONS
V
BST
- V
LX
= 5V
V
SUP
= 4.5V to 28V, V
SUPSW
= 14V,
T
A
= +25°C
V
SUP
= 4.5V to 28V, V
SUPSW
= 14V
1.5
1.5
MIN
TYP
1.7
1.8
1.8
200
300
0.01
20
1.0
1.0
0.02
1000
110
94
R
FOSC
= 25.5kI, V
SUP
= 4.5V to 28V
Oscillator Frequency
Oscillator Frequency Range
EXTERNAL CLOCK INPUT (FSYNC)
External Input Clock Acquisition
Time
External Input Clock Frequency
t
FSYNC
(Note 3)
f
OSC
+
10%
1.4
0.4
500
f
SW
= 400kHz
f
SW
= 1.0MHz
4
1.6
0.8
1
Cycles
Hz
V
V
kI
ms
ms
V
f
OSC
R
FOSC
= 61.9kI, V
SUP
= 4.5V to 28V
R
FOSC
= 120kI, V
SUP
= 4.5V to 28V (Note 3)
(Note 3)
348
191
220
1.0
400
220
452
249
1000
1.01
V
1.015
%/V
FS
ns
%
MHz
kHz
kHz
kHz
550
1
mA
mI
FA
nA
MAX
2.5
2.0
UNITS
mA
A
TRANSCONDUCTANCE AMPLIFIER (COMP)
FB Regulation Voltage
FB Line Regulation
Transconductance (from FB to
COMP)
Minimum On-Time
Cold-Crank Event Duty Cycle
OSCILLATOR FREQUENCY
DV
LINE
g
m
t
ON
DC
CC
External Input Clock High Threshold V
FSYNC_HI
V
FSYNC
rising
External Input Clock Low Threshold V
FSYNC_LO
V
FSYNC
falling
FSYNC Pulldown Resistance
Soft-Start Time
ENABLE INPUT (EN)
Enable On Threshold Voltage Low
V
EN_LO
R
FSYNC
t
SS
½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½
Maxim Integrated Products
3
*The
parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
ELECTRICAL CHARACTERISTICS* (continued)
(V
SUP
= V
SUPSW
= 14V, V
EN
= 14V, L1 = 22FH, C
IN
= 4.7FF, C
OUT
= 100FF, C
BIAS
= 1FF, C
BST
= 0.1FF, C
CRES
= 1nF, R
FOSC
=
61.9kI, T
A
= T
J
= -40NC to +125NC, unless otherwise noted. Typical values are at T
A
= +25NC.)
PARAMETER
Enable On Threshold Voltage High
Enable Threshold Voltage
Hysteresis
Enable Input Current
RESET
Reset Internal Switching Level
RESETI Threshold Voltage
CRES Threshold Voltage
CRES Threshold Hysteresis
RESETI Input Current
CRES Source Current
CRES Pulldown Current
RES
Output Low Voltage
RES
Leakage Current (Open-
Drain Output)
Reset Debounce Time
t
RES_DEB
V
TH_RISING
V
FB
rising, V
RESETI
= 0V
V
TH_FALLING
V
FB
falling, V
RESETI
= 0V
V
RESETI_HI
V
RESETI
falling
V
CRES_HI
V
CRES_HYS
I
RESET
I
CRES
I
CRES_PD
V
RESETI
= 0V
V
OUT
in regulation
V
OUT
out of regulation
I
SINK
= 5mA
V
OUT
in regulation
V
RESETI
falling
T
A
= +25°C
T
A
= +125°C
20
25
9.5
1
0.4
1
V
CRES
rising
93
91
1.05
1.07
95
93
1.25
1.13
0.05
0.02
10
10.5
96.5
95
1.4
1.19
%V
FB
V
V
V
FA
FA
mA
V
FA
nA
Fs
SYMBOL
V
EN_HI
V
EN,HYS
I
EN
CONDITIONS
MIN
2.2
0.2
10
TYP
MAX
UNITS
V
V
nA
Note 2:
When 3V < V
OUT
< 5.5V, the bias regulator is connected to the output to save quiescent current, V
BIAS
= V
OUT
.
Note 3:
Guaranteed by design; not production tested.
½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½
Maxim Integrated Products
4
*The
parametric values (min, typ, max limits) shown in the Electrical Characteristics table supersede values quoted elsewhere in this data sheet.
MAX16975
28V, 1.2A Automotive Step-Down Converter
with Low Operating Current
Typical Operating Characteristics
(V
SUP
= V
SUPSW
= 14V, V
EN
= 14V, L1 = 4.7FH, C
IN
= 4.7FF, C
OUT
= 22FF, C
BIAS
= 1FF, C
BST
= 0.1FF, C
CRES
= 1nF, R
FOSC
=
61.9kI, T
A
= +25NC, unless otherwise noted.)
STARTUP WITH FULL LOAD
(OUT = 1.25V, f
SW
= 400kHz)
EFFICIENCY vs. LOAD CURRENT
OUT
1V/div
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
0
0
400
I
LOAD
(mA)
800
1200
3.3V/400kHz
5V/400kHz
1.25V/400kHz
8V/400kHz
MAX16975 toc02
MAX16975 toc01
100
I
LOAD
= 1.2A
0V
0V
RES
5V/div
EN
5V/div
SUP
5V/div
0V
0V
2ms/div
SWITCHING FREQUENCY
vs. LOAD CURRENT (1.25V/400kHz)
MAX16975 toc03
SWITCHING FREQUENCY vs. R
FOSC
5V OUTPUT
MAX16975 toc04
402.0
1200
1000
800
600
400
200
PWM MODE
SWITCHING FREQUENCY (kHz)
401.6
401.2
400.8
400.4
400.0
200
450
700
I
LOAD
(mA)
950
SWITCHING FREQUENCY (kHz)
1200
10
32
54
76
98
120
R
FOSC
(kI)
SWITCHING FREQUENCY vs. TEMPERATURE
(1.25V/400kHz, 5V/400kHz)
I
LOAD
= 1.2A, R
FOSC
= 64.87kI
MAX16975 toc05
LOAD-STEP RESPONSE
(1.25V/400kHz)
MAX16975 toc06
450
430
0 TO 1.25A LOAD STEP
SWITCHING FREQUENCY (kHz)
5V/400kHz
410
0
390
370
0
350
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
4ms/div
1.25V/400kHz
V
OUT
AC-COUPLED
V
OUT
100mV/div
I
LOAD
1A/div
½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½½
Maxim Integrated Products
5
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