___________Product Selection Guide
_______________General Description
The MAX787/MAX788/MAX789 are monolithic, bipolar,
pulse-width modulation (PWM), switch-mode, step-down
DC-DC regulators. Each is rated at 5A. Very few external
components are needed for standard operation because
the power switch, oscillator, feedback, and control circuitry
are all on-chip. Employing a classic buck topology, these
regulators perform high-current step-down functions.
The MAX787/MAX788/MAX789 have excellent dynamic
and transient response characteristics, while featuring
cycle-by-cycle current limiting to protect against overcurrent
faults and short-circuit output faults. They also have a wide
8V to 40V input range.
Each regulator is available in a 5-pin TO-220 package.
These devices have a preset 100kHz oscillator frequency
and a preset current limit of 6.5A. See the MAX724/
MAX726 data sheet for more applications information.
_______________________Applications
Distributed Power from High-Voltage Buses
High-Current, High-Voltage Step-Down
Multiple-Output Buck Converter
MAX787/MAX788/MAX789
5V/3.3V/3V 5A Step-Down, PWM,
Switch-Mode DC-DC Regulators
________________________________________________________________
Maxim Integrated Products
1
V
IN
V
SW
GND
V
C
SENSE
CASE IS CONNECTED TO GROUND. STANDARD PACKAGE HAS STAGGERED LEADS.
CONTACT FACTORY FOR STRAIGHT LEADS.
5-PIN TO-220
FRONT VIEW
MAX787
MAX788
MAX789
1
2
3
4
5
__________________Pin Configuration
VIN
VC
VSW
220
F
GND
2.7k
0.01
F
OUTPUT
5V AT 5A
SENSE
50
H
MBR745
470
F
INPUT
8V TO 40V
MAX787
STEP-DOWN CONVERTER
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0182; Rev 3; 9/95
___________________________Features
o
Input Range: Up to 40V
o
5A On-Chip Power Switch
o
Fixed Outputs: 5V (MAX787)
3.3V (MAX788)
3V (MAX789)
o
100kHz Switching Frequency
o
Excellent Dynamic Characteristics
o
Few External Components
o
8.5mA Quiescent Current
o
TO-220 Package
______________Ordering Information
PART
V
OUT
(V)
I
OUT
MAX (A)
MAX724
Adjustable
5
MAX728
3.3
2
MAX726
Adjustable
2
MAX727
5
2
MAX787
5
5
MAX788
3.3
5
MAX789
3
5
MAX729
3
2
PART
MAX787
CCK
MAX787ECK
MAX788
CCK
MAX788ECK
-40C to +85C
0C to +70C
TEMP. RANGE
PIN-PACKAGE
5 TO-220
5 TO-220
-40C to +85C
0C to +70C
5 TO-220
5 TO-220
MAX789
CCK
MAX789ECK
-40C to +85C
0C to +70C
5 TO-220
5 TO-220
MAX787/MAX788/MAX789
5V/3.3V/3V 5A Step-Down, PWM,
Switch-Mode DC-DC Regulators
2
_______________________________________________________________________________________
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45V
Switch Voltage with Respect to Input Voltage. . . . . . . . . . . . . . . . 50V
Switch Voltage with Respect to GND Pin (V
SW
negative)
(Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35V
SENSE Pin Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V, +10V
Operating Temperature Ranges
MAX78_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +70C
MAX78_ECK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40C to +85C
Junction Temperature Ranges
MAX78_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +125C
MAX78_ECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 40C to +125C
Storage Temperature Range . . . . . . . . . . . . . . . . . . . -65C to +160C
Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300C
ELECTRICAL CHARACTERISTICS
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
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.
ABSOLUTE MAXIMUM RATINGS
PARAMETER
CONDITIONS
Start-Up Mode (Note 4)
3.5
5.0
MIN
TYP
MAX
UNITS
Switching Frequency Line Regulation
8V
V
IN
40V
Switch-Current Limit (Note 5)
5.5
6.5
8.5
A
T
j
< 0C
90
100
110
T
j
0C
85
120
V
OUT
= V
SENSE
= 0V (Note 5)
20
Switching Frequency
kHz
0.03
0.10
%/V
Error-Amplifier Voltage Gain
1V
V
C
4V
2000
V/V
Error-Amplifier Transconductance
3000
5000
9000
mho
Error-Amplifier Source Current
V
SENSE
= V
OUT
- 10%
100
140
225
T
j
= +25C
A
Error-Amplifier Sink Current
I
SW
= 1A
V
SENSE
= V
OUT
+ 10%
0.6
1.0
1.7
1.85
T
j
+125C
mA
T
j
= +25C
T
j
= +25C
Switch-On Voltage (Note 1)
T
j
= +25C
T
j
= +25C
2.10
V
T
j
= +25C
Supply Current (Note 3)
mA
V
IN
40V, V
SENSE
= 5.5V
8.5
11
Minimum Supply Voltage
Normal Mode
7.3
8.0
V
3.5
4.8
T
j
= +25C
T
j
= +25C
V
IN
=
25V, V
SW
= 0V
5
300
Switch-Off Leakage
V
IN
= 40V, V
SW
= 0V
10
500
A
T
j
< 0C
T
j
0C
I
SW
= 5A
2.30
2.50
Input Supply Voltage Range
8.0
40.0
V
Maximum Duty Cycle
85
90
%
T
j
0C
T
j
< 0C
MAX787/MAX788/MAX789
5V/3.3V/3V 5A Step-Down, PWM,
Switch-Mode DC-DC Regulators
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
MIN
TYP
MAX
UNITS
4.85
5.00
5.15
V
3.20
3.30
3.40
SENSE Voltage
V
C
= 2V
2.90
3.00
3.10
3.0
5.0
8.0
k
2.5
4.2
7.0
SENSE Pin Divider Resistance
T
j
= +25C
2.2
3.8
6.5
CONDITIONS
MAX787
MAX788
MAX789
MAX787
MAX788
MAX789
T
j
= +25C
0.5
2.0
%
Output Voltage Tolerance
V
OUT
(nominal) = 5V (MAX787),
3.3V (MAX788), or 3V (MAX789);
all conditions of input voltage,
output voltage, and load
current
T
j
= T
MIN
to
T
MAX
1.0
3.0
8V
V
IN
40V
0.005
0.020
%/V
Output Voltage Line Regulation
T
j
= +25C
1.5
V
C
Voltage
T
j
= T
MIN
to T
MAX
-4
V
2.5
C/W
Thermal Resistance Junction to Case
(Note 6)
mV/C
V
C
Voltage Temperature Coefficient
0% duty cycle
0% duty cycle
Note 1:
Do not exceed switch-to-input voltage limitation.
Note 2:
For switch currents between 1A and 5A, maximum switch-on voltage can be calculated via linear interpolation.
Note 3:
By setting the SENSE pin to 5.5V, the V
C
pin is forced to its low clamp level and the switch duty cycle is forced to zero,
approximating the zero load condition.
Note 4:
For proper regulation, total voltage from V
IN
to GND must be
8V after start-up.
Note 5:
To avoid extremely short switch-on times, the switch frequency is internally scaled down when V
SENSE
is less than 2.6V
(MAX787), 2.0V (MAX788), or 1.8V (MAX789). Switch-current limit is tested with V
SENSE
adjusted to give a 1s minimum
switch-on time.
Note 6:
Guaranteed, not production tested.
______________________________________________________________Pin Description
V
IN
supplies power to the internal circuitry and also connects to the collector of the internal power
switch. V
IN
must be bypassed with a low-ESR capacitor, typically 200F or 220F.
Internal Power Switch Output. The
S
witch output can swing 35V below ground and is rated for 5A.
Ground requires a short, low-noise connection to ensure good load regulation. The internal reference
is referred to GND, so errors at this pin are multiplied by the error amplifier.
Error-Amplifier Output. A series RC network connected to this pin compensates the MAX787/MAX788/
MAX789. Output swing is limited to about 5.8V in the positive direction and -0.7V in the negative direc-
tion. V
C
can also synchronize the MAX787/MAX788/MAX789 to an external TTL clock in the 115kHz to
170kHz range. See MAX724/MAX726 data sheet.
SENSE Input is the internal error amplifier's input, and should be directly connected to V
OUT
. SENSE
also aids current limiting by reducing oscillator frequency when V
OUT
is low.
V
IN
V
SW
GND
V
C
SENSE
5
NAME
4
3
2
1
FUNCTION
PIN
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
4
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
1995 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
MAX787/MAX788/MAX789
5V/3.3V/3V 5A Step-Down, PWM,
Switch-Mode DC-DC Regulators
E
F
B
DIM
A
B
C1
D
E
e
F
H1
J1
L
P
Q
MIN
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.500
0.139
0.100
MAX
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.580
0.161
0.120
MIN
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
12.70
3.54
2.54
MAX
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
14.73
4.08
3.04
INCHES
MILLIMETERS
e
21-4737-
5-PIN TO-220
(STRAIGHT LEAD)
PACKAGE
1.70 BSC
0.067 BSC
P
H1
Q
D
A
J1
C1
L
CONTACT FACTORY FOR AVAILABILITY
________________________________________________________Package Information
E
J3
F
B
DIM
A
B
C1
D
E
e
F
H1
J1
J2
J3
L
L1
L2
P
Q
MIN
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.170
0.327
0.170
0.260
0.700
0.139
0.100
MAX
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.185
0.335
0.200
0.340
0.720
0.161
0.120
MIN
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
4.32
8.31
4.32
6.60
17.78
3.54
2.54
MAX
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
4.70
8.51
5.08
8.64
18.29
4.08
3.04
INCHES
MILLIMETERS
e
21-005-
5-PIN TO-220
(STAGGERED LEAD)
PACKAGE
1.70 BSC
0.067 BSC
P
H1
Q
D
A
L2
J1
L1
L
C1
J2
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