19-0546; Rev 0; 5/06
12V/5V Input Buck PWM Controller
General Description
The MAX5951 is a 12V pulse-width modulated (PWM),
step-down, DC-DC controller. The device operates over
the input-voltage range of 8V to 16V or 5V ±10%, and
provides an adjustable output from 0.8V to 5.5V. The
device delivers up to 10A of load current with excellent
load-and-line regulation.
The MAX5951 PWM section utilizes a voltage-mode
control scheme for good noise immunity and offers
external compensation, allowing for maximum flexibility
with a wide selection of inductor values and capacitor
types. The device operates at a fixed switching fre-
quency that is programmable from 100kHz to 1MHz
and can be synchronized to an external clock signal
though the SYNCIN input. The device includes under-
voltage lockout (UVLO) and digital soft-start. Protection
features include lossless valley-mode current limit, hic-
cup-mode output short-circuit protection, and thermal
shutdown.
The MAX5951 is available in a space-saving 5mm x
5mm, 32-pin thin QFN package and is specified for
operation over the -40°C to +85°C extended tempera-
ture range. Refer to the MAX5950 data sheet for a pin-
compatible PWM controller with hot swap.
Features
♦
8V to 16V or 5V ±10% Input-Voltage Range
♦
Lossless Valley-Mode Current Sensing
♦
Output Voltage Adjustable from 0.8V to 5.5V
♦
Voltage-Mode Control
♦
External Compensation for Maximum Flexibility
♦
Digital Soft-Start
♦
Sequencing or Ratiometric Tracking
♦
Startup Synchronization
♦
Programmable PGOOD Output
♦
Programmable Switching Frequency from 100kHz
to 1MHz
♦
External Frequency Synchronization
♦
SYNCIN and SYNCOUT Enable 180° Out-of-Phase
Operation
♦
Thermal Shutdown and Short-Circuit Protection
♦
Space-Saving, 5mm x 5mm, 32-Pin TQFN Package
MAX5951
Ordering Information
PART
MAX5951ETJ+
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
32 TQFN
PKG
CODE
T3255-4
Applications
PCI-e Express Modules™
General 12V or 5V Input PWM Controllers
Blade Servers
RAID
Base Stations
Workstations
+Denotes
lead-free package.
Pin Configuration
ILIM
CS+
TOP VIEW
STARTUP
18
PGOOD
SENSE
COMP
24
CS- 25
PGND 26
DL 27
DREG 28
LX 29
DH 30
BST 31
REG 32
23
22
21
FB
20
19
17
16
15
14
13
SYNCIN
SYNCOUT
AGND
THRESH
DCENI
N.C.
N.C.
N.C.
MAX5951
RT
12
11
10
9
8
N.C.
+
1
IN
2
PUVLO
3
N.C.
4
N.C.
5
IN
6
N.C.
7
N.C.
PCI-e Express Modules is a trademark of PCI-SIG.
TQFN
(5mm x 5mm)
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
12V/5V Input Buck PWM Controller
MAX5951
ABSOLUTE MAXIMUM RATINGS
IN to AGND.............................................................-0.3V to +24V
BST to AGND..........................................................-0.3V to +30V
BST to LX..................................................................-0.3V to +6V
CS- to AGND ...............................................-0.3V to (V
IN
+ 0.3V)
REG, DREG, PUVLO, DCENI, SYNCIN, THRESH,
SENSE to AGND....................................................-0.3V to +6V
RT, ILIM, STARTUP, PGOOD, FB, CS+ to AGND ....-0.3V to +6V
SYNCOUT, COMP to AGND.....................-0.3V to (V
REG
+ 0.3V)
DL to PGND...............................................-0.3V to (V
DREG
+ 6V)
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
PGND to AGND .....................................................-0.3V to +0.3V
Input Current (any pin) .....................................................±50mA
Continuous Power Dissipation (T
A
= +70°C)
32-Pin TQFN (derate 34.5 mW/°C above +70°C) .2758.6mW
32-Pin TQFN (θ
JA
) ....................................................+29°C/W
32-Pin TQFN (θ
JC
) ...................................................+2.1°C/W
Operating Ambient Temperature Range .............-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) ......…………………..+300°C
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= 12V or V
IN
= V
REG
= 5V, V
DREG
= V
REG
, V
PGND
= 0V, V
SYNCIN
= 0V, R
RT
= 100kΩ, R
ILIM
= 60kΩ, C
REG
= 2.2µF, T
A
= T
J
=
-40°C to +85°C, unless otherwise noted. Typical values are at T
A
= T
J
= +25°C.) (Note 1)
PARAMETER
Input-Voltage Range
Standby Supply Current
Quiescent Supply Current
Switching Supply Current
PWM UVLO
Default PWM Undervoltage
Lockout Threshold
PWM Undervoltage Lockout
Hysteresis
PUVLO Threshold
PUVLO Hysteresis
PUVLO Input Impedance
PWM DCENI CONTROL
DCENI Comparator Input
Common-Mode Range
DCENI Comparator Offset
DCENI Comparator Hysteresis
DCENI Input Current
THRESH Operating Voltage
Range
THRESH Input Current
Default DCENI Threshold
V
THRESH
> 0.6V
V
THRESH
< 0.3V
V
THRESH
< 0.3V
-1
0.6
-1.5
-5
1.202
1.22
V
DCENI
- V
THRESH
0
-10
100
+1
2.5
+1
+1
1.238
3
+10
V
mV
mV
µA
V
µA
V
180
V
PUVLO
V
PUVLO
rising
1.202
V
IN
rising
6.7
0.7
1.220
122
310
500
1.238
7.3
V
V
V
mV
kΩ
SYMBOL
V
IN
CONDITIONS
V
IN
= V
REG
= V
DREG
(Note 2)
V
IN
= 16V, V
PUVLO
= 0V
V
IN
= 16V, V
FB
= 0.9V
V
IN
= 16V, V
FB
= 0V
MIN
8
4.5
0.3
1.6
5.0
TYP
MAX
16
5.5
0.5
2.6
8.0
UNITS
V
mA
mA
mA
2
_______________________________________________________________________________________
12V/5V Input Buck PWM Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V or V
IN
= V
REG
= 5V, V
DREG
= V
REG
, V
PGND
= 0V, V
SYNCIN
= 0V, R
RT
= 100kΩ, R
ILIM
= 60kΩ, C
REG
= 2.2µF, T
A
= T
J
=
-40°C to +85°C, unless otherwise noted. Typical values are at T
A
= T
J
= +25°C.) (Note 1)
PARAMETER
PWM PGOOD OUTPUT
SENSE Threshold
SENSE Hysteresis
SENSE Input Bias Current
PGOOD Internal Pullup Current
PGOOD Output Voltage Low
INTERNAL VOLTAGE REGULATOR
Output Voltage Set Point
Line Regulation
Load Regulation
PWM OSCILLATOR
Oscillator Frequency Range
f
SW
V
SYNCIN
= 0V, f
SW
= 5 x 10
10
/ R
RT
Hz
T
A
= T
J
= +25°C
Oscillator Accuracy
T
A
= T
J
= -40°C to +85°C
RT Voltage
Maximum Duty Cycle
SYNCIN High-Level Voltage
SYNCIN Low-Level Voltage
SYNCIN Pulldown Resistor
SYNCIN Rising to SYNCOUT
Falling Delay
SYNCIN Falling to SYNCOUT
Rising Delay
Maximum SYNCIN Frequency
SYNCOUT Voltage High
SYNCOUT Voltage Low
PWM ERROR AMPLIFIER
FB Input Range
FB Input Current
COMP Output Voltage Range
Open-Loop Gain
Unity-Gain Bandwidth
Reference Voltage
f
GBW
V
REF
I
COMP
= -500µA to +500µA
792
I
COMP
= -500µA to +500µA
0
-250
0.25
80
2.5
800
808
V
REF
+250
V
REG
-
0.5
V
nA
V
dB
MHz
mV
VH
SYNCOUT
I
SYNCOUT
= +1.2mA
VL
SYNCOUT
I
SYNCOUT
= -2.4mA
1
V
REG
-
0.1
50
50
100
10
30
V
RT
50kΩ < R
RT
< 500kΩ
V
SYNCIN
= 0V, V
IN
= 12V
82
2.1
0.8
150
f
SW
< 500kHz
f
SW
> 500kHz
f
SW
< 500kHz
f
SW
> 500kHz
100
-2.5
-4
-3.5
-5
2
88
1000
+2.5
+4
+3.5
+5
kHz
%
%
V
%
V
V
kΩ
ns
ns
MHz
V
mV
V
REG
V
IN
= 8V to 16V
I
REG
= 0 to 50mA
4.7
5.3
1
150
V
mV/V
mV
I
PGOOD
= -2.4mA
-1
10
50
V
SENSE
rising
788
800
100
+1
812
mV
mV
µA
µA
mV
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX5951
_______________________________________________________________________________________
3
12V/5V Input Buck PWM Controller
MAX5951
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V or V
IN
= V
REG
= 5V, V
DREG
= V
REG
, V
PGND
= 0V, V
SYNCIN
= 0V, R
RT
= 100kΩ, R
ILIM
= 60kΩ, C
REG
= 2.2µF, T
A
= T
J
=
-40°C to +85°C, unless otherwise noted. Typical values are at T
A
= T
J
= +25°C.) (Note 1)
PARAMETER
PWM COMPARATOR
Comparator Offset Voltage
Comparator Propagation Delay
PWM DIGITAL SOFT-START
Soft-Start Duration
Reference Voltage Steps
PWM RAMP GENERATOR
Ramp Amplitude
PWM CURRENT-LIMIT COMPARATOR AND HICCUP MODE
Cycle-by-Cycle Valley Current-
Limit Threshold Adjustment
Range
Cycle-by-Cycle Valley Current-
Limit Threshold Tolerance
ILIM Reference Current
ILIM Reference Current Tempco
CS+, CS- Input Bias Current
PWM HICCUP MODE
Number of Cumulative Current-
Limit Events to Hiccup
Number of Consecutive
Noncurrent-Limit Cycles to Clear
N
CL
Hiccup Timeout
PWM STARTUP INPUT
STARTUP Threshold
STARTUP Threshold Hysteresis
Internal Pullup Current
STARTUP Output Voltage Low
PWM DH DRIVER
Peak Source Current
Peak Sink Current
DH Resistance Sourcing
DH Resistance Sinking
V
DH,LX
= 0V, pulse width < 100ns,
V
BST,LX
= 5V
V
DH,LX
= 5V, pulse width < 100ns,
V
BST,LX
= 5V
I
DH
= 50mA, V
BST,LX
= 5V
I
DH
= -50mA, V
BST,LX
= 5V
2
2
1
1
3
3
A
A
Ω
Ω
I
START
I
STARTUP
= -2.4mA
V
SUT
1.1
250
10
0.1
1.9
V
mV
µA
V
N
CL
8
Clocks
V
CS+
= 0V, V
CS-
= -0.3V, current out of the
CS_
-1
Limit = V
ILIM
/ 10
V
ILIM
= 0.5V
V
ILIM
= 3.5V
V
ILIM
= 0 to 3.5V, T
A
= T
J
= +25°C
50
44.5
330
19
20
3333
+20
350
55.5
366
21
mV
1.8
V
1024
128
6.3
Clocks
Steps
mV
0.3
40
V
ns
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
mV
µA
ppm/°C
µA
N
CLR
N
HT
3
512
Clocks
Clocks
4
_______________________________________________________________________________________
12V/5V Input Buck PWM Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V or V
IN
= V
REG
= 5V, V
DREG
= V
REG
, V
PGND
= 0V, V
SYNCIN
= 0V, R
RT
= 100kΩ, R
ILIM
= 60kΩ, C
REG
= 2.2µF, T
A
= T
J
=
-40°C to +85°C, unless otherwise noted. Typical values are at T
A
= T
J
= +25°C.) (Note 1)
PARAMETER
PWM DL DRIVER
Peak Source Current
Peak Sink Current
DL Resistance Sourcing
DL Resistance Sinking
Break-Before-Make Time
THERMAL SHUTDOWN
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
T
J
rising
135
15
°C
°C
V
DL
= 0V, pulse width < 100ns,
V
DREG
= 5V
V
DL
= 5V, pulse width < 100ns,
V
DREG
= 5V
I
DL
= 50mA, V
DREG
= 5V
I
DL
= -50mA, V
DREG
= 5V
2
2
1
1
25
3
3
A
A
Ω
Ω
ns
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX5951
Note 1:
Limits at -40°C are guaranteed by design and are not production tested.
Note 2:
For 5V applications, connect REG directly to IN.
Typical Operating Characteristics
(Typical
Operating Circuits.
V
IN
= 12V or V
IN
= V
REG
= 5V, V
DREG
= V
REG
, V
PGND
= 0V, V
SYNCIN
= 0V, R
RT
= 49.9kΩ, R
ILIM
= 48.7kΩ,
C
REG
= 2.2µF, T
A
= +25°C.)
DEFAULT DCENI THRESHOLD
vs. TEMPERATURE
MAX5951 toc01
SENSE THRESHOLD
vs. TEMPERATURE
MAX5951 toc02
REG OUTPUT VOLTAGE
vs. TEMPERATURE
MAX5951 toc03
1.30
808
5.15
5.10
5.05
V
REG
(V)
1.27
DCENI THRESHOLD (V)
1.24
SENSE THRESHOLD (mV)
804
800
5.00
4.95
1.21
796
1.18
792
4.90
4.85
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
1.15
-40
-15
10
35
60
85
788
-40
TEMPERATURE (°C)
_______________________________________________________________________________________
5
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