19-0171; Rev 1; 9/93
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
_______________General Description
The MAX747 high-efficiency, high-current, step-down
controller drives external P-channel FETs. It provides
90% to 95% efficiency from a 6V supply with load
currents ranging from 50mA up to 2.5A. It uses a
pulse-width-modulating (PWM) current-mode control
scheme to provide precise output regulation and low
output noise. The MAX747’s 4V to 15V input voltage
range, a fixed 5V/adjustable (Dual-Mode™) output, and
a current limit set with an external resistor make this
device ideal for a wide range of applications.
High efficiency is maintained with light loads due to a
proprietary dual-control (Idle-Mode™) scheme that
minimizes switching losses by reducing the switching
frequency at light loads. The low 800µA quiescent
current and ultra-low 0.6µA shutdown current further
extend battery life.
External components are protected by the MAX747’s
cycle-by-cycle current limit. The MAX747 also features a
2V ±1.5% reference, a comparator for low-battery
detection or level translating, as well as soft-start and
shutdown capability.
The MAX746, discussed in a separate data sheet,
functions similarly to the MAX747, but it drives N-channel
logic level FETs on the high side.
____________________________Features
o
90% to 95% Efficiency for 50mA to 2.5A
Output Currents
o
4V to 15V Input Voltage Range
o
Low 800µA Supply Current
o
0.6µA Shutdown Current
o
Drives External P-Channel FETs
o
Cycle-by-Cycle Current Limiting
o
2V ±1.5% Accurate Reference Output
o
Adjustable Soft-Start
o
Precision Comparator for Power-Fail or
Low-Battery Warning
MAX747
______________Ordering Information
PART
MAX747CPD
MAX747CSD
MAX747C/D
MAX747EPD
MAX747ESD
MAX747MJD
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
14 Plastic DIP
14 Narrow SO
Dice*
14 Plastic DIP
14 Narrow SO
14 CERIDIP
* Contact factory for dice specifications.
________________________Applications
Notebook Power Supplies
Personal Digital Assistants
Battery-Operated Equipment
Cellular Phones
5V to 3.3V Green PC Applications
__________Typical Operating Circuit
INPUT
6V TO 15V
V+
AV+
5OmΩ
100µF
MAX747
CS
EXT
P
5OµH
OUTPUT
5V
2.3A
__________________Pin Configuration
TOP VIEW
ON/OFF
SHDN
430µF
LBI
SS
REF
SHDN
FB
CC
1
2
3
4
5
6
14
LBO
13
GND
OUT
LOW-BATTERY
DETECTOR
INPUT
LBI
0.1µF
MAX747
12
V+
11
EXT
10
AGND
9
8
CS
OUT
REF
SS
LBO
CC FB AGND GND
LOW-BATTERY
DETECTOR
OUTPUT
AV+
7
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
P-Channel DC-DC Controller
MAX747
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V+, AV+ to GND ..............................-0.3V to 17V
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 10.00mW/°C above +70°C) ..........800mW
SO (derate 8.33mW/°C above +70°C) .........................667mW
CERDIP (derate 9.09mW/°C above +70°C) .................727mW
Operating Temperature Ranges:
MAX747C_D .......................................................0°C to +70°C
MAX747E_D.....................................................-40°C to +85°C
MAX747MJD ..................................................-55°C to +125°C
Junction Temperature
MAX747C_D/E_D .........................................................+150°C
MAX747MJD ...............................................................+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
= 0mA, I
REF
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Input Voltage Range
Output Voltage
Feedback Voltage
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
Supply Current
Oscillator Frequency
Maximum Duty Cycle
CS Amp I
LIM
Threshold
EXT Output High
EXT Output Low
EXT Sink Current
EXT Source Current
CC Impedance
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
2
SYMBOL
CONDITIONS
V+
For regulated outputs
V+ = 6V to 15V, 0V < V+ - CS < 0.125V, FB = 0V
V
OUT
(includes line and load regulation)
V+ - CS = 0V, external MAX747C
feedback mode
MAX747E/M
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
OUT
= 5V
For dual-mode switchover
FB = 2V
MAX747C
V
REF
I
REF
= 0µA
MAX747E/M
I
REF
= 0µA to 100µA
SS = 0V
SS = 2V
Operating, V+ = 15V
Operating, V+ = 10V
Shutdown mode
MAX747C
f
OSC
MAX747E/M
V+ = 6V
V
LIMIT
V+ - CS
I
EXT
= -1mA (sourcing)
I
EXT
= 1mA (sinking)
V
EXT
= 7.5V
V
EXT
= 2.5V
V
TH
LBI falling
MAX747C
MAX747EM
MIN
4
4.85
1.96
1.95
TYP
5.08
2.00
2.00
0.05
1.3
91
50
0.1
2.00
2.00
9
1
500
0.95
0.8
0.6
100
100
96
150
MAX
15
5.25
2.04
2.05
0.1
2.5
80
40
100
2.03
2.04
20
UNITS
V
V
V
%V
%
%
µA
mV
nA
V
mV
µA
µA
mA
µA
kHz
%
mV
V
V
mA
mA
kΩ
V
V
nA
µA
V
V
nA
1.97
1.96
100
1.3
20
115
120
175
0.25
85
80
91
125
V+ – 0.1
1.97
1.96
110
170
24
2.00
2.00
I
SINK
= 0.5mA
LBI = 2.5V
V+ = 15V, LBO = 15V, LBI = 2.5V
V
IL
V
IH
SHDN = 10V
2.0
0.1
2.03
2.04
0.4
100
1
0.4
100
_______________________________________________________________________________________
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, V+ = 9V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs.
TEMPERATURE
MAX747-TOC1
MAX747
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
MAX747-TOC2
PEAK INDUCTOR CURRENT vs.
OUTPUT CURRENT (V
OUT
= 5V)
MAX747-TOC5
4
V
IN
= 9V
V
OUT
= 5V
SUPPLY CURRENT (mA)
3
1.0
3
PEAK INDUCTOR CURRENT (A)
SUPPLY CURRENT (mA)
0.9
2
2
ENTIRE
CIRCUIT
1
SCHOTTKY DIODE
LEAKAGE EXCLUDED
0
-75
-50 -25
0
25
50
75
100 125
TEMPERATURE (°C)
0.8
1
V
IN
= 12V
V
IN
= 9V
V
IN
= 6V
0.7
0.6
5
7
9
11
13
15
SUPPLY VOLTAGE (V)
0
0.01
0.1
1
10
OUTPUT CURRENT (A)
PEAK INDUCTOR CURRENT vs.
OUTPUT CURRENT (V
OUT
= 3.3V)
MAX747-TOC6
EFFICIENCY vs. OUTPUT CURRENT
(V
OUT
= 5V)
V
IN
= 6V
MAX1747-TOC7
EFFICIENCY vs. OUTPUT CURRENT
(V
OUT
= 3.3V)
MAX747-TOC8
3
PEAK INDUCTOR CURRENT (A)
100
100
VIN = 6V
EFFICIENCY (%)
EFFICIENCY (%)
2
90
V
IN
= 9V
90
VIN = 9V
VIN = 12V
80
V
IN
= 9V
1
V
IN
= 6V
V
IN
= 5V
0
0.01
80
V
IN
= 12V
0.1
1
10
70
0.01
0.1
1
10
70
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
CONTINUOUS-CONDUCTION MODE BOUNDARY
AND CORRESPONDING PEAK INDUCTOR CURRENT (V
OUT
= 3.3V)
MAX747-TOC3
CONTINUOUS-CONDUCTION MODE BOUNDARY
AND CORRESPONDING PEAK INDUCTOR CURRENT (V
OUT
= 5V)
DISCONTINUOUS
CONDUCTION
REGION
PEAK INDUCTOR
CURRENT
V
OUT
= 5V
L = 50µH
R
SENSE
= 50mΩ
MAX747-TOC4
18
V
OUT
= 3.3V
L = 33µH
R
SENSE
= 50mΩ
SUPPLY VOLTAGE (V)
14
DISCONTINUOUS
CONDUCTION
REGION
PEAK
INDUCTOR
CURRENT
CONTINUOUS
CONDUCTION
REGION
2.0
PEAK INDUCTOR CURRENT (A)
15
2.0
PEAK INDUCTOR CURRENT (A)
13
SUPPLY VOLTAGE (V)
1.6
1.6
11
9
10
1.2
1.2
6
0.8
7
CONTINUOUS
CONDUCTION
REGION
0.8
2
0.4
0.6
0.8
1.0
1.2
1.4
OUTPUT CURRENT (A)
0.4
5
0.5
0.7
0.9
1.1
1.3
OUTPUT CURRENT (A)
0.4
_______________________________________________________________________________________
3
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
MAX747
____________________________Typical Operating Characteristics (continued)
CONTINUOUS-CONDUCTION MODE WAVEFORMS
MAX747-SCOPE1
DISCONTINUOUS-CONDUCTION IDLE-MODE WAVEFORMS
MAX747-SCOPE2
a
a
b
b
c
20µs/div
V+ = 9V, I
OUT
= 125mA
a) EXT VOLTAGE, 10V/div
b) INDUCTOR CURRENT, 200mA/div
c) V
OUT
RIPPLE, 50mV/div
c
5µs/div
V+ = 9V, I
OUT
= 2.5A
a) EXT VOLTAGE, 10V/div
b) INDUCTOR CURRENT, 1A/div
c) V
OUT
RIPPLE, 50mV/div
LINE-TRANSIENT RESPONSE
MAX747-SCOPE4
MAX747-SCOPE5
LOAD-TRANSIENT RESPONSE
a
a
b
b
5ms/div
I
OUT
= 2.0A
a) V+ = 6V to 12V, 5V/div
b) V
OUT
RIPPLE, 100mV/div
MAX747-SCOPE3
100µs/div
V+ = 9V, C
OUT
= 430µF
a) LOAD CURRENT, 0.1A TO 2.5A, 1A/div
b) V
OUT
RIPPLE, 100mV/div
MODERATE LOAD, IDLE-MODE WAVEFORMS
a
b
c
5µs/div
V+ = 9V, I
OUT
= 560mA
a) EXT VOLTAGE, 5V/div
b) INDUCTOR CURRENT, 0.5A/div
c) V
OUT
RIPPLE 100mV/div
4
_______________________________________________________________________________________
High-Efficiency PWM, Step-Down
P-Channel DC-DC Controller
MAX747
______________________________________________________________Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
NAME
LBI
SS
REF
SHDN
FB
CC
AV+
OUT
CS
AGND
EXT
V+
GND
LBO
FUNCTION
Input to the internal low-battery comparator. Tie to V+ or GND if not used.
Soft-start limits start-up surge currents. On power-up, it charges the soft-start capacitor, slowly raising the
peak current limit to the level set by the sense resistor.
2V reference output that can source 100µA for external loads. Bypass with 0.22µF. The reference is
disabled in shutdown mode.
Active-high TTL/CMOS logic-level input. In shutdown mode, V
OUT
= 0V and the supply current is reduced
to 20µA.
Feedback input for adjustable-output operation. Connect to GND for fixed +5V output. Use a resistor
divider network to adjust the output voltage. See the section
Setting the Output Voltage.
Compensation capacitor. AC compensation input for the error amplifier. Connect a capacitor between CC
and GND for fixed +5V output operation. See
Compensation Capacitor
section.
Quiet supply voltage for sensitive analog circuitry. A bypass capacitor is not required for AV+.
Output voltage sense input. Connects to internal resistor divider. Leave unconnected for adjustable output.
Bypass to AGND with a 0.1µF capacitor close to the IC.
Negative input to the current-sense amplifier. Connect the current-sense resistor (R
SENSE
) from V+ to CS.
Quiet analog ground
Power MOSFET gate drive output that swings between V+ and GND. EXT is not protected against short
circuits to V+ or AGND.
High-current supply voltage for the output driver
High-current ground return for the output driver
Low-battery output is an open-drain output that goes low when LBI is less than 2V. Connect to V+ through
a pull-up resistor. Leave floating if not used. LBO is disabled in shutdown mode.
____________________Getting Starting
Figure 1a shows the 5V output 11.4W standard
application circuit and Figure 1b shows the 3.3V output
7.5W standard application circuit. Most applications
will be served by these circuits. To learn more about
component selection for particular applications, refer to
the
Design Procedure
section. To learn more about the
operation of the MAX747, refer to the
Detailed
Description.
_______________Detailed Description
The MAX747 monolithic, CMOS, step-down switch-
mode power-supply controller drives external
P-channel FETs. It uses a unique current-mode pulse-
width-modulating (PWM) control scheme that results in
high efficiency over a wide range of load currents, tight
output voltage regulation, excellent load- and line-
transient response, and low noise. Efficiency at light
loads is further enhanced by a proprietary Idle-Mode
switching control scheme that skips oscillator cycles in
order to reduce switching losses.
_______________________________________________________________________________________
5
京公网安备 11010802033920号
EEWORLD
