19-5781; Rev 0; 3/11
IT
TION K
VALUA
E
BLE
AVAILA
36V, 1MHz Step-Down Controller
with Low Operating Current
General Description
Features
♦
♦
♦
♦
♦
♦
♦
Wide 3.5V to 36V Input Voltage Range
42V Input Transient Tolerance
High Duty Cycle During Undervoltage Transients
220kHz to 1MHz Adjustable Switching Frequency
Current-Mode Control Architecture
Adjustable (1V to 13V) Output Voltage with ±2%
Accuracy
Three Operating Modes
50µA Ultra-Low Quiescent Current Skip Mode
Forced Fixed-Frequency Mode
External Frequency Synchronization
Lowest BOM Count, Current-Mode Control
Architecture
Power-Good Output
Enable Input Compatible from 3.3V Logic Level to
42V
Current-Limit, Thermal Shutdown, and
Overvoltage Protection
-40°C to +125°C Automotive Temperature Range
Automotive Qualified
MAX16955
The MAX16955 is a current-mode, synchronous PWM
step-down controller designed to operate with input volt-
ages from 3.5V to 36V while using only 50μA of quies-
cent current at no load. The switching frequency is
adjustable from 220kHz to 1MHz by an external resistor
and can be synchronized to an external clock up to
1.1MHz. The MAX16955 output voltage is pin program-
mable to be either 5V fixed, or adjustable from 1V to
13V. The wide input voltage range, along with its ability
to operate in dropout during undervoltage transients,
makes it ideal for automotive and industrial applications.
The MAX16955 operates in fixed-frequency PWM mode
and low quiescent current skip mode. It features an
enable logic input, which is compatible up to 42V to
disable the device and reduce its shutdown current to
10μA. Protection features include overcurrent limit,
overvoltage, undervoltage, and thermal shutdown with
automatic recovery. The device also features a power-
good monitor to ease power-supply sequencing.
The MAX16955 is available in a thermally enhanced 16-
pin TSSOP package with exposed pad and is specified
for operation over the -40°C to +125°C automotive tem-
perature range.
♦
♦
♦
♦
♦
♦
Typical Operating Circuit
V
BAT
C
IN
SUP
DH
BST
LX
C
BST
L
NH
Applications
Automotive
Industrial
Military
Point of Load
R
COMP
C
COMP2
COMP
Ordering Information
PART
MAX16955AUE/V+
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
16 TSSOP-EP*
C
COMP1
MAX16955
PGOOD
EN
FSYNC
FOSC
R
FOSC
SGND
DL
PGND
CS
OUT
FB
BIAS
C
L
NL
R
SENSE
/V denotes an automotive qualified part.
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
V
OUT
5V
C
OUT
________________________________________________________________
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.
36V, 1MHz Step-Down Controller
with Low Operating Current
MAX16955
ABSOLUTE MAXIMUM RATINGS
SUP and EN to SGND ............................................-0.3V to +42V
LX to PGND ..............................................................-1V to +42V
BST to LX .................................................................-0.3V to +6V
BIAS, FB, PGOOD, FSYNC to SGND .......................-0.3V to +6V
DH to LX ...................................................................-0.3V to +6V
DL to PGND .............................................-0.3V to (V
BIAS
+ 0.3V)
FOSC to SGND ........................................-0.3V to (V
BIAS
+ 0.3V)
CS and OUT to SGND .........................................-0.3V to +12.7V
*As
per JEDEC51 standard (multilayer board).
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.
PGND to SGND .....................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
TSSOP (derate 26.1mW/°C above +70°C) .............2088.8mW*
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PACKAGE THERMAL CHARACTERISTICS (Note 1)
TSSOP
Junction-to-Ambient Thermal Resistance (θ
JA
) .........38.3°C/W
Junction-to-Case Thermal Resistance (θ
JC
) ...................3°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
EN
= 14V, C
IN
= 10μF, C
OUT
= 94μF, C
BIAS
= 2.2μF, C
BST
= 0.1μF, R
FOSC
= 76.8kΩ, T
A
= T
J
= -40°C to +125°C, unless
otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
SUP Input Voltage Range
SUP Operating Supply Current
Skip Mode Supply Current
SUP Shutdown Supply Current
BIAS Voltage
BIAS Undervoltage Lockout
BIAS Undervoltage Lockout
Hysteresis
BIAS Minimum Load
OUTPUT VOLTAGE (OUT)
Output Voltage Adjustable
Range
OUT Pulldown Resistance
Output Voltage (5V Fixed Mode)
FB Feedback Voltage
(Adjustable Mode)
FB Current
R
PULL_D
V
OUT
V
FB
I
FB
V
EN
= 0V or fault condition active
V
SUP
= 6V to 36V, V
FB
= V
BIAS
, fixed-
frequency mode (Note 4)
V
SUP
= 6V to 36V, 0V < (V
CS
- V
OUT
)
< 80mV, fixed-frequency mode
V
FB
= 1.0V
4.925
0.99
1.0
30
5.0
1.0
0.02
5.075
1.01
V
V
μA
13
V
I
BIAS(MIN)
SYMBOL
V
SUP
I
SUP
I
SKIP
I
SHDN,SUP
V
BIAS
V
UVBIAS
(Note 3)
Fixed 5V output, fixed-frequency, PWM
mode, V
FB
= V
BIAS
, no external FETs
connected
No load, fixed 5V output
V
EN
= 0V
V
SUP
= 3.5V, I
BIAS
= 45mA
6V < V
SUP
< 36V
V
BIAS
rising
V
BIAS
falling
V
SUP
- V
BIAS
> 200mV
4.7
CONDITIONS
MIN
3.5
1
50
10
3.0
5.0
3.1
200
45
5.3
3.4
90
20
TYP
MAX
36
UNITS
V
mA
μA
μA
V
V
mV
mA
2
_______________________________________________________________________________________
36V, 1MHz Step-Down Controller
with Low Operating Current
ELECTRICAL CHARACTERISTICS (continued)
(V
SUP
= V
EN
= 14V, C
IN
= 10μF, C
OUT
= 94μF, C
BIAS
= 2.2μF, C
BST
= 0.1μF, R
FOSC
= 76.8kΩ, T
A
= T
J
= -40°C to +125°C, unless
otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
FB Line Regulation
Transconductance (from FB to
COMP)
Error-Amplifier Output
Impedance
Operating Frequency
Minimum On-Time
Maximum FSYNC Frequency
Minimum FSYNC Frequency
FSYNC Switching Threshold
High
FSYNC Switching Threshold Low
FSYNC Internal Pulldown
Resistance
CURRENT LIMIT
CS Input Current
Output Input Current
CS Current-Limit Voltage
Threshold
FAULT DETECTION
Output Overvoltage Trip
Threshold
Output Overvoltage Trip
Hysteresis
Output Overvoltage Fault
Propagation Delay
Output Undervoltage Trip
Threshold
Output Undervoltage Trip
Hysteresis
Output Undervoltage
Propagation Delay
PGOOD Output Low Voltage
PGOOD Leakage Current
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
V
PGOOD,L
I
PGOOD
T
SHDN
(Note 5)
(Note 5)
Falling edge
Rising edge (excluding startup)
I
SINK
= 3mA
1
+175
15
t
OVP
V
FB,UV
Rising edge
Falling edge
V
OUT
= V
FB
; with respect to slewed FB
threshold, falling edge
83
V
FB,OV
V
OUT
= V
FB
, rising edge
108
113
2.5
25
25
88
2.5
25
25
0.4
93
118
%V
FB
%
μs
%V
FB
%
μs
V
μA
°C
°C
I
CS
I
OUT
V
LIMIT
V
CS
= V
OUT
= 0V or V
BIAS
(Note 4)
During normal operation
V
FB
= V
BIAS
V
CS
- V
OUT
, V
BIAS
= 5V, V
OUT
2.5V
68
-1
22
32
80
92
+1
μA
μA
mV
g
m,EA
R
OUT,EA
f
SW
t
ON(MIN)
f
FSYNC(MAX)
f
FSYNC(MIN)
V
FSYNC,HI
V
FSYNC,LO
1
f
FSYNC
> 110% of internal frequency (20%
duty cycle), f
SW
= 220kHz
1.4
0.4
R
FOSC
= 76.8k
R
FOSC
= 30.1k
360
SYMBOL
CONDITIONS
V
EN
= V
SUP
, 6V < V
SUP
< 36V (Note 4)
MIN
TYP
0.02
1200
30
400
1000
80
1100
242
440
MAX
UNITS
%/V
μS
M
kHz
ns
kHz
kHz
V
V
M
MAX16955
_______________________________________________________________________________________
3
36V, 1MHz Step-Down Controller
with Low Operating Current
MAX16955
ELECTRICAL CHARACTERISTICS (continued)
(V
SUP
= V
EN
= 14V, C
IN
= 10μF, C
OUT
= 94μF, C
BIAS
= 2.2μF, C
BST
= 0.1μF, R
FOSC
= 76.8kΩ, T
A
= T
J
= -40°C to +125°C, unless
otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
GATE DRIVE
DH Gate-Driver On-Resistance
DL Gate-Driver On-Resistance
DH/DL Dead Time (Note 4)
BST Input Current
BST On-Resistance
ENABLE INPUT
EN Input Threshold Low
EN Input Threshold High
EN Threshold Voltage
Hysteresis
EN Input Current
SOFT-START
Soft-Start Ramp Time
t
SS
5
ms
I
EN
V
EN,LO
V
EN,HI
2.2
0.2
0.5
1.2
V
V
V
μA
R
DH
R
DL
t
DEAD
I
BST
(V
BST
- V
LX
) forced to 5V
(V
BST
- V
LX
) forced to 0V
DL = high state
DL = low state
DL rising (Note 5)
DH rising (Note 5)
V
LX
= 0V, V
BST
= 5V,
V
DH
- V
LX
= V
DL
- V
PGND
= 0V
(Note 5)
10
2
3.5
2
60
60
1
5
15
ns
μA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Note 2:
Note 3:
Note 4:
Note 5:
Devices tested at T
A
= +25°C. Limits over temperature are guaranteed by design.
For 3.5V operation, the n-channel MOSFET’s threshold voltage should be compatible to (lower than) this input voltage.
Device not in dropout condition.
Guaranteed by design; not production tested.
4
_______________________________________________________________________________________
36V, 1MHz Step-Down Controller
with Low Operating Current
Typical Operating Characteristics
(V
SUP
= V
EN
= 14V, C
IN
= 10μF, C
OUT
= 94μF, C
BIAS
= 2.2μF, C
BST
= 0.1μF, R
FOSC
= 66.5kΩ, f
OSC
= 468kHz, V
FB
= V
BIAS
,
V
OUT
= 5V, T
A
= +25°C, unless otherwise noted.)
V
OUT
= 3.3V STARTUP RESPONSE
(SKIP MODE)
V
OUT
= 5V STARTUP RESPONSE
(SKIP MODE)
10V/div
V
OUT
2V/div
MAX16955
MAX16955 toc01
MAX16955 toc02
10V/div
V
OUT
2V/div
I
OUT
2A/div
I
OUT
2A/div
5V/div
V
PGOOD
2ms
2ms
5V/div
V
PGOOD
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX16955 toc03
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX16955 toc04
EFFICIENCY vs. LOAD CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
FIXED-FREQUENCY MODE
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
LOAD CURRENT (A)
V
OUT
= 5V
V
OUT
= 3.3V
MAX16955 toc05
40
35
SUPPLY CURRENT (mA)
30
25
20
15
10
5
0
6
100
90
80
SUPPLY CURRENT (µA)
70
60
50
40
30
20
10
0
FIXED-FREQUENCY MODE
SKIP MODE
100
12
18
24
30
36
6
12
18
24
30
36
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
EFFICIENCY vs. LOAD CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.0001
SKIP MODE
MAX16955 toc06
SWITCHING FREQUENCY vs. R
FOSC
1200
1150
1100
1050
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
R
FOSC
(kI)
MAX16955 toc07
100
V
OUT
= 5V
FREQUENCY (kHz)
10
V
OUT
= 3.3V
0.001
0.01
0.1
1
25 35 45 55 65 75 85 95 105 115 125 135 145
LOAD CURRENT (A)
_______________________________________________________________________________________
5
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