19-0192; Rev 1; 11/93
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
_______________General Description
The MAX746 is a high-efficiency, high-current, step-down
DC-DC power-supply controller that drives external N-chan-
nel FETs. It provides 93% to 96% efficiency from a 6V supply
voltage with load currents ranging from 50mA up to 3A. It
uses a pulse-width-modulating (PWM) current-mode control
scheme to provide precise output regulation and low output
noise. The MAX746's 4V to 15V input voltage range, fixed
5V/adjustable (Dual-Mode
TM
) output, and adjustable current
limit make this device ideal for a wide range of applications.
High efficiency is maintained with light loads due to a propri-
etary automatic pulse-skipping control (Idle-Mode
TM
) scheme
that minimizes switching losses by reducing the switching fre-
quency at light loads. The low 950µA quiescent current and
ultra-low 1.4µA shutdown current further extend battery life.
External components are protected by the MAX746's cycle-
by-cycle current limit. The MAX746 also features a 2V ±1.5%
reference, a comparator for low-battery detection or level
translating, and soft-start and shutdown capability.
The MAX747—discussed in a separate data sheet—
functions similarly to the MAX746, but drives P-channel logic
level FETs.
____________________________Features
o
93% to 96% Efficiency for 50mA to 3A
Output Currents
o
4V to 15V Input Voltage Range
o
Low 950µA Supply Current
o
1.4µA Shutdown Current
o
Drives External N-Channel FETs
o
Fixed-Frequency Current-Mode PWM (Heavy Loads)
o
Idle-Mode PFM (Light Loads)
o
Cycle-by-Cycle Current Limiting
o
2V ±1.5% Accurate Reference Output
o
Adjustable Soft-Start
o
Undervoltage Lockout
o
Precision Comparator for Power-Fail or
Low-Battery Warning
MAX746
______________Ordering Information
PART
MAX746CPE
MAX746CSE
MAX746C/D
MAX746EPE
MAX746ESE
MAX746MJE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
16 CERDIP
________________________Applications
5V-to-3.3V Green PC Applications
Notebook/Laptop Computers
Personal Digital Assistants
Battery-Operated Equipment
Cellular Phones
* Contact factory for dice specifications.
__________Typical Operating Circuit
__________________Pin Configuration
INPUT 6V TO 15V
V+
TOP VIEW
AV+
40mΩ
CP
HIGH
SHDN
ON/OFF
LOW-BATTERY
DETECTOR INPUT
LBI
REF
SS
OUT
LBO
CC FB AGND GND
LBO
1
LBI
2
16
GND
15
V+
14
CP
MAX746
CS
EXT
39µH
OUTPUT
5V
440µF
SS
3
REF
4
SHDN
5
FB
6
CC
7
AV+
8
MAX746
13
HIGH
12
EXT
11
AGND
10
CS
9
OUT
LOW-BATTERY
DETECTOR OUTPUT
DIP/SO
™Dual-Mode and Idle-Mode are trademarks of Maxim Integrated Products.
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
MAX746
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V+, AV+ to GND ..............................-0.3V to 17V
HIGH, EXT to GND....................................................-0.3V to 21V
AGND to GND..........................................................-0.3V to 0.3V
All Other Pins................................................-0.3V to (V+ + 0.3V)
Reference Current (I
REF
) ....................................................±2mA
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW
Narrow SO (derate 8.70mW/°C above +70°C) ............696mW
CERDIP (derate 10.00mW/°C above +70°C) ...............800mW
Operating Temperature Ranges:
MAX746C_E ........................................................0°C to +70°C
MAX746E_E .....................................................-40°C to +85°C
MAX746MJE ..................................................-55°C to +125°C
Junction Temperatures:
MAX746C_E/E_E..........................................................+150°C
MAX746MJE.................................................................+175°C
Storage Temperature Range .............................-65°C to +160°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
(V+ = 10V, I
LOAD
= 0A, I
REF
= 0µA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Input Voltage
Output Voltage
SYMBOL
V+
V
OUT
V+ = 6V to 15V, 0V < (V+ - CS) < 0.125V,
FB = 0V (includes line and load regulation)
(V+ - CS) = 0V,
external feedback mode
V+ = 6V to 15V, FB = 0V
V+ = 4V to 15V, external feedback mode
0V < (V+ - CS) < 0.125V
Circuit of Figure 1, I
LOAD
= 0.5A to 2.5A,
V+ = 6V
V
OUT
= 5V
For dual-mode switchover
FB = 2V
V
REF
I
REF
= 0µA
I
REF
= 0µA to 100µA
SS = 0V
SS = 2V
Operating, V+ = 15V
Supply Current (Note 2)
I
SUPP
Operating, V+ = 10V
Shutdown mode
Oscillator Frequency
f
OSC
MAX746C
MAX746E/M
85
80
MAX746C
MAX746E/M
0.95
1.4
100
100
20
115
120
µA
kHz
0.5
100
MAX746C
MAX746E/M
1.97
1.96
1
2.00
2.00
9
1.0
500
1.1
1.4
1.7
mA
1.3
94
50
80
40
100
2.03
2.04
20
1.5
MAX746C
MAX746E/M
CONDITIONS
MIN
4
4.85
1.96
1.95
5.08
2.00
2.00
0.05
0.1
2.5
TYP
MAX
15
5.25
2.04
2.05
UNITS
V
V
Feedback Voltage
V
FB
V
Line Regulation
Load Regulation
Efficiency
OUT Leakage Current
FB Input Logic Low
FB Input Leakage Current
Reference Voltage
Reference Load Regulation
Soft-Start Source Current
Soft-Start Fault Current (Note 1)
%/V
%
%
µA
mV
nA
V
mV
µA
µA
2
_______________________________________________________________________________________
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
MAX746
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 10V, I
LOAD
= 0A, I
REF
= 0µA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Maximum Duty Cycle
Charge-Pump Output Voltage
Current-Sense Amplifier
Current-Limit Threshold
EXT Output High
EXT Output Low
EXT Sink Current
EXT Source Current
Compensation Pin Impedance
MAX746C
LBI Threshold Voltage
LBO Output Voltage Low
LBI Input Leakage Current
LBO Output Leakage Current
SHDN Input Voltage Low
SHDN Input Voltage High
SHDN Input Leakage Current
Note 1:
Note 2:
V
IL
V
IH
SHDN = 10V
2.0
0.1
100
V
OL
LBI falling
MAX746E/M
I
SINK
= 0.5mA
LBI = 2.5V
V+ = 15V, LBO = 15V, LBI = 2.5V
1.96
2.00
2.04
0.4
100
1
0.4
V
nA
µA
V
V
nA
1.97
V
HIGH
V
LIMIT
SYMBOL
V+ = 6V
I
HIGH
= 0mA to 10mA
V+ – CS
V
HIGH
forced to 15V, I
EXT
= -1mA
V
HIGH
forced to 15V, I
EXT
= 1mA
V
HIGH
= 15V, V
EXT
= 12.5V
V
HIGH
= 15V, V
EXT
= 2.5V
160
270
24
2.00
2.03
V
CONDITIONS
MIN
91
V+ + 4
125
V
HIGH
- 0.1
0.25
TYP
96
V+ + 5 V+ + 6
150
175
MAX
UNITS
%
V
mV
V
V
mA
mA
kΩ
The soft-start fault current is the current sink capability of SS when V
REF
< 1V or when the device is in shutdown.
I
SUPP
is the supply current drawn by V+, which includes the current drawn by the charge pump. The charge pump
doubles the current drawn by HIGH from the V+ input, so I
SUPP
= I
V+
+ 2I
HIGH
.
_______________________________________________________________________________________
3
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
MAX746
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1a, T
A
= +25°C, unless otherwise noted.)
N0-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX746-01
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
MAX746-02
CONTINUOUS-CONDUCTION MODE
BOUNDARY AND CORRESPONDING
PEAK INDUCTOR CURRENT
DISCONTINUOUS-
CONDUCTION REGION
13
SUPPLY VOLTAGE (V)
PEAK
INDUCTOR
CURRENT
MAX746-09
1.2
NO-LOAD SUPPLY CURRENT (mA)
4
NO-LOAD SUPPLY CURRENT (mA)
V+ = 9V
V
OUT
= 5V
3
15
1.1
11
1.0
2
ENTIRE
CIRCUIT
1
SCHOTTKY DIODE
LEAKAGE EXCLUDED
-75 -50 -25
0
25
50
75
100 125
9
7
CONTINUOUS-
CONDUCTION
REGION
0.7
0.9
1.1
1.3
1.5
1.7
0.9
0.8
5
7
9
11
13
SUPPLY VOLTAGE (V)
15
0
5
OUTPUT CURRENT (A)
TEMPERATURE (°C)
EFFICIENCY vs. OUTPUT CURRENT
MAX746-07
EFFICIENCY vs. OUTPUT CURRENT
MAX746-08
EFFICIENCY vs. OUTPUT CURRENT
CIRCUIT OF FIGURE 1c
VOUT = 5V
VIN = 6V
EFFICIENCY (%)
90
VIN = 12V
MAX746-06
100
100
CIRCUIT OF FIGURE 1b
VOUT = 3.3V
V+ = 5V
EFFICIENCY (%)
90
100
EFFICIENCY (%)
90
VIN = 6V
VIN = 9V
VIN = 12V
80
80
80
CIRCUIT OF FIGURE 1a
V
OUT
= 5V
70
0.01
0.1
1
10
OUTPUT CURRENT (A)
70
0.01
0.1
1
10
OUTPUT CURRENT (A)
70
0.01
0.1
1
10
OUTPUT CURRENT (A)
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
CIRCUIT OF FIGURE 1a
V
OUT
= 5V
3
MAX746-03
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
MAX746-05
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
CIRCUIT OF FIGURE 1c
VOUT = 5V
1.0
VIN = 12V
0.5
MAX746-03
4
PEAK INDUCTOR CURRENT (A)
4
PEAK INDUCTOR CURRENT (A)
CIRCUIT OF FIGURE 1b
VOUT = 3.3V
V+ = 5V
1.5
PEAK INDUCTOR CURRENT (A)
3
2
VIN = 12V
1
VIN = 9V
0
0.01
0.1
1
10
OUTPUT CURRENT (A)
VIN = 6V
2
1
VIN = 6V
0
0.01
0.1
1
10
OUTPUT CURRENT (A)
0
0.01
0.1
1
10
OUTPUT CURRENT (A)
4
_______________________________________________________________________________________
High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1a, T
A
= +25°C, unless otherwise noted.)
MAX746
LOAD-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
10V
A
8V
A
A
B
B
B
200µs/div
A: LOAD CURRENT, 0.1A TO 1.5A, 1A/div
B: V
OUT
RIPPLE, 50mV/div, AC-COUPLED
V+ = 10V
1ms/div
A: LOAD CURRENT, 0.1A TO 1.5A, 1A/div
B: V
OUT
RIPPLE, 50mV/div, AC COUPLED
V+ = 10V
500ms/div
A: V+ = 8V TO 10V, 2V/div
B: V
OUT
RIPPLE, 100mV/div
I
OUT
= 3A
CONTINUOUS-CONDUCTION MODE
WAVEFORMS
A
DISCONTINUOUS-CONDUCTION
IDLE-MODE WAVEFORMS
MODERATE-LOAD, IDLE-MODE
WAVEFORMS
A
A
B
B
0V
C
C
B
C
5µs/div
A : EXT VOLTAGE, 20V/div
B : INDUCTOR CURRENT 1A/div
C : V
OUT
RIPPLE, 50mV/div
V+ = 10V, I
OUT
= 3A
20µs/div
A: EXT VOLTAGE, 10V/div
B: INDUCTOR CURRENT, 500mA/div
C: V
OUT
RIPPLE, 50mV/div, AC-COUPLED
V+ = 10V, I
OUT
= 75mA
20µs/div
A: EXT VOLTAGE, 10V/div
B: INDUCTOR CURRENT, 500mA/div
C: V
OUT
RIPPLE, 50mV/div, AC-COUPLED
V+ = 6V, I
OUT
= 480mA
_______________________________________________________________________________________
5
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