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19-1321; Rev 1; 2/98
IT
TION K
VALUA
E
BLE
AVAILA
Miniature, Low-Voltage,
Precision Step-Down Controller
General Description
____________________________Features
o
±2% DC Accuracy
o
0.1% (typ) DC Load Regulation
o
Adjustable Switching Frequency to 350kHz
o
Idle Mode™ Pulse-Skipping Operation
o
1.10V to 5.5V Adjustable Output Voltage
o
3.15V Minimum IC Supply Voltage (at V
CC
pin)
o
Internal Digital Soft-Start
o
1.1V ±2% Reference Output
o
1µA Total Shutdown Current
o
Output Overvoltage Crowbar Protection
o
Output Undervoltage Shutdown (foldback)
o
Tiny 16-Pin QSOP Package
MAX1637
The MAX1637 synchronous, buck, switch-mode power-
supply controller generates the CPU supply voltage in
battery-powered systems. The MAX1637 is a stripped-
down version of the MAX1636 in a smaller 16-pin QSOP
package. The MAX1637 is intended to be powered sep-
arately from the battery by an external bias supply (typi-
cally the +5V system supply) in applications where the
battery exceeds 5.5V. The MAX1637 achieves excellent
DC and AC output voltage accuracy. This device can
operate from a low input voltage (3.15V) and delivers the
excellent load-transient response needed by upcoming
generations of dynamic-clock CPUs.
Using synchronous rectification, the MAX1637 achieves
up to 95% efficiency. Efficiency is greater than 80%
over a 1000:1 load-current range, which extends bat-
tery life in system-suspend or standby mode. Excellent
dynamic response corrects output load transients
caused by the latest dynamic-clock CPUs within five
300kHz clock cycles. Powerful 1A on-board gate driv-
ers ensure fast external N-channel MOSFET switching.
The MAX1637 features a logic-controlled and synchro-
nizable, fixed-frequency, pulse-width-modulation
(PWM) operating mode. This reduces noise and RF
interference in sensitive mobile-communications and
pen-entry applications. Asserting the
SKIP
pin enables
fixed-frequency mode, for lowest noise under all load
conditions. For a stand-alone device that includes a
+5V VL linear regulator and low-dropout capabilities,
refer to the MAX1636 data sheet.
______________Ordering Information
PART
MAX1637EEE
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
16 QSOP
__________Typical Operating Circuit
V
BIAS
V
BATT
________________________Applications
Notebook Computers
Handy-Terminals, PDAs
Subnotebook Computers
V
CC
SHDN
V
GG
MAX1637
DH
BST
LX
OUTPUT
__________________Pin Configuration
TOP VIEW
CSH 1
CSL 2
FB 3
CC 4
REF 5
SHDN 6
SYNC 7
GND 8
16 SKIP
15 LX
14 DH
CC
REF
SKIP
SYNC
GND
DL
PGND
CSH
CSL
FB
MAX1637
13 BST
12 PGND
11 DL
10 V
GG
9
V
CC
QSOP
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
Miniature, Low-Voltage,
Precision Step-Down Controller
MAX1637
ABSOLUTE MAXIMUM RATINGS
GND to PGND .............................................................+2V to -2V
LX, BST to GND......................................................-0.3V to +36V
BST, DH to LX...........................................................-0.3V to +6V
V
CC
, V
GG
, CSL, CSH,
SHDN
to GND.......................-0.3V to +6V
DL to GND..................................................-0.3V to (V
GG
+ 0.3V)
REF,
SKIP,
SYNC, CC to GND ...................-0.3V to (V
CC
+ 0.3V)
REF Output Current.............................................................20mA
REF Short-Circuit to GND ..............................................Indefinite
Operating Temperature Range ...........................-40°C to +85°C
Continuous Power Dissipation (T
A
= +70°C)
QSOP (derate 8.3mW/°C above +70°C) ......................667mW
Storage Temperature Range .............................-65°C to +160°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10sec) .............................+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
(Circuit of Figure 1, V
CC
= V
GG
= 5V, SYNC = V
CC
, I
REF
= 0mA,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
SMPS CONTROLLER
Input Voltage Range
Output Voltage
Output Adjustment Range
Current-Limit Threshold
Power Consumption
Shutdown Supply Current
FB Input Current
Soft-Start Ramp Time
Idle-Mode Switchover Threshold
AC Load Regulation
INTERNAL REFERENCE
V
CC
Undervoltage Lockout Threshold
V
GG
Undervoltage Lockout Threshold
REF Output Voltage
REF Load Regulation
REF Line Regulation
OSCILLATOR
Oscillator Frequency
Maximum Duty Factor
SYNC Input Pulse Width High
SYNC Input Pulse Width Low
SYNC Input Rise/Fall Time
SYNC Input Frequency Range
(Note 1)
240
SYNC = V
CC
SYNC = GND
SYNC = V
CC
SYNC = GND
270
170
89
93
200
200
200
340
300
200
92
96
330
230
kHz
%
ns
ns
ns
kHz
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 15mV
REF load = 0µA
REF load = 0µA to 50µA
V
CC
= 3.15V to 5.5V
2.80
2.80
1.080
1.100
3.05
3.05
1.120
10
3
V
V
V
mV
mV
V
CC
, V
GG
FB tied to V
OUT
, 0mV < (CSH - CSL) < 80mV,
includes line and load regulation
V
CC
= 5V
V
CC
= 3.3V
CSH > CSL
CSH < CSL
Output not switching
SHDN
= GND, V
CC
= V
GG
V
FB
= V
REF
SHDN
to full current limit, four levels
CSH - CSL
CSH - CSL = 0mV to CSH - CSL = 100mV
20
-50
512
30
2
40
V
CC
= V
GG
= 5V
V
CC
= V
GG
= 3.3V
3.15
1.080
V
REF
V
REF
80
-145
100
-100
1.5
1
0.5
1.100
5.5
1.120
5.5
3.6
120
-55
2.5
1.75
3
50
V
V
V
mV
mW
µA
nA
clocks
mV
%
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Miniature, Low-Voltage,
Precision Step-Down Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= V
GG
= 5V, SYNC = V
CC
, I
REF
= 0mA,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
OVERVOLTAGE PROTECTION
Overvoltage Trip Threshold
Overvoltage Fault Propagation Delay
Output Undervoltage Lockout Delay
INPUTS AND OUTPUTS
Logic Input Voltage High
Logic Input Voltage Low
Logic Input Bias Current
Current-Sense Input Leakage Current
Gate Driver Sink/Source Current
Gate Driver On-Resistance
SHDN, SKIP,
SYNC
SHDN, SKIP,
SYNC
Pin at GND or V
CC
CSH = CSL = 5V, V
CC
= V
GG
= GND,
either CSH or CSL input
DH or DL forced to 2V
High or low, DH or DL
1
7
-1
2.4
0.8
1
10
V
V
µA
µA
A
Ω
FB, with respect to regulation point
FB to DL delay, 22mV overdrive, C
GATE
= 2000pF
60
From shutdown or power-on-reset state
4
7
1.25
70
6144
80
10
%
µs
%
clocks
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1637
Output Undervoltage Lockout Threshold % of nominal output
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
CC
= V
GG
= 5V, SYNC = V
CC
, I
REF
= 0mA,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
SMPS CONTROLLER
Input Voltage Range
Output Voltage
Output Adjustment Range
Current-Limit Threshold
Power Consumption
INTERNAL REFERENCE
V
CC
Undervoltage Lockout Threshold
V
GG
Undervoltage Lockout Threshold
OSCILLATOR
Oscillator Frequency
SYNC Input Pulse Width High
SYNC Input Pulse Width Low
SYNC Input Rise/Fall Time
SYNC Input Frequency Range
240
SYNC = V
CC
SYNC = GND
262
170
200
200
200
340
338
230
kHz
ns
ns
ns
kHz
Rising edge, hysteresis = 15mV
Rising edge, hysteresis = 15mV
2.80
2.80
3.05
3.05
V
V
V
CC
, V
GG
FB tied to V
OUT
, 0mV < (CSH - CSL) < 80mV,
includes line and load regulation
V
CC
= 5V
V
CC
= 3.3V
CSH > CSL
V
CC
= V
GG
= 5V, output not switching
V
CC
= V
GG
= 3.3V, output not switching
3.15
1.080
V
REF
V
REF
70
5.5
1.120
5.5
3.6
130
2.5
1.75
V
V
V
mV
mW
mW
CONDITIONS
MIN
TYP
MAX
UNITS
_______________________________________________________________________________________
3
Miniature, Low-Voltage,
Precision Step-Down Controller
MAX1637
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= V
GG
= 5V, SYNC = V
CC
, I
REF
= 0mA,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
OVERVOLTAGE PROTECTION
Overvoltage Trip Threshold
INPUTS AND OUTPUTS
Logic Input Voltage High
Logic Input Voltage Low
SHDN, SKIP,
SYNC
SHDN, SKIP,
SYNC
2.4
0.8
V
V
FB, with respect to regulation point
4.0
60
10
80
%
%
Output Undervoltage Lockout Threshold % of nominal output
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Guaranteed by design, not production tested.
Note 2:
Specifications from -40°C to 0°C are guaranteed by design and not production tested.
__________________________________________Typical Operating Characteristics
(V
OUT
= 3.3V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(1.7V/7A CIRCUIT)
MAX1637-01
EFFICIENCY vs. LOAD CURRENT
(2.5V/3A CIRCUIT)
90
80
EFFICIENCY (%)
70
60
50
40
30
V
BATT
= 7V
SKIP = LOW
V
BATT
= 22V
V
BATT
= 15V
EFFICIENCY (%)
MAX1637-02
EFFICIENCY vs. LOAD CURRENT
(2.5V/2A CIRCUIT)
SKIP = LOW
90
V
BATT
= 7V
MAX1637-03
100
SKIP = LOW
90
EFFICIENCY (%)
V
BATT
= 7V
100
100
80
V
BATT
= 15V
V
BATT
= 22V
80
V
BATT
= 22V
70
70
V
BATT
= 15V
60
20
10
60
50
0.01
0.1
1
10
LOAD CURRENT (A)
0
0.001
0.01
0.1
LOAD CURRENT (A)
1
10
50
0.01
0.1
1
10
LOAD CURRENT (A)
EFFICIENCY vs. LOAD CURRENT
(3.3V/3A CIRCUIT)
SKIP = LOW
90
EFFICIENCY (%)
MAX1637-04
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
I
LOAD
= 1A
V
OUT
= 3.3V
15
MAX1637-06
SUPPLY CURRENT
vs. LOAD CURRENT
SKIP = LOW
15
MAX1637-07
100
20
V
CC
+ V
GG
SUPPLY CURRENT (mA)
20
V
CC
+ V
GG
SUPPLY CURRENT (mA)
80
V
BATT
= 15V
V
BATT
= 30V
V
BATT
= 5V
10
SKIP = HIGH
10
SYNC = HIGH
70
5
SKIP = LOW
5
SYNC = LOW
60
50
0.01
0.1
1
10
LOAD CURRENT (A)
0
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
0
0
1
2
3
4
5
6
7
8
9
LOAD CURRENT (A)
4
_______________________________________________________________________________________
Miniature, Low-Voltage,
Precision Step-Down Controller
____________________________________Typical Operating Characteristics (continued)
(V
OUT
= 3.3V, T
A
= +25°C, unless otherwise noted.)
LOAD REGULATION
vs. LOAD CURRENT
MAX1637-08
MAX1637
REF LOAD-REGULATION ERROR
vs. REF LOAD CURRENT
MAX1637-09
DROPOUT VOLTAGE
vs. LOAD CURRENT
800
DROPOUT VOLTAGE (mV)
700
600
500
400
300
200
100
V
OUT
FORCED TO 3.27V
SYNC = V
CC
MAX1637-10
10
8
LOAD REGULATION
∆V
OUT
(mV)
6
4
2
0
-2
-4
-6
-8
-10
0.01
0.1
1
0.6
REF LOAD REGULATION
∆V
(mV)
0.5
0.4
0.3
0.2
0.1
0
900
0
0
10 20 30 40 50 60 70 80 90 100
REF LOAD CURRENT (µA)
0.01
0.1
1
10
LOAD CURRENT (A)
10
LOAD CURRENT (A)
LOAD-TRANSIENT RESPONSE
(3.3V/3A, PWM MODE)
MAX1637 TOC11
LOAD-TRANSIENT RESPONSE
(1.8V, PWM MODE)
MAX1637 TOC12
V
OUT
50mV/div
V
OUT
50mV/div
4A
LOAD
2A CURRENT
0A
10A
5A LOAD CURRENT
0A
100µs/div
100µs/div
SWITCHING WAVEFORMS
(PWM MODE)
MAX1637-13
SWITCHING WAVEFORMS
(PFM MODE)
MAX1637-14
SWITCHING WAVEFORMS
DROPOUT OPERATION
MAX1637-15
V
OUT
= 1.7V
V
OUT
20mV/div
V
OUT
50mV/div
SYNC = V
CC
V
OUT
10mV/div
5V
V
LX
0V
1A
0A
INDUCTOR
CURRENT
5V
0V
1A
0A
V
LX
V
LX
2V/div
1A
0A
V
OUT
FORCED TO 3.27V
INDUCTOR
CURRENT
INDUCTOR
CURRENT
1µs/div
20µs/div
1µs/div
_______________________________________________________________________________________
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