_______________General Description
The MAX767 is a high-efficiency, synchronous buck
controller IC dedicated to converting a fixed 5V supply
into a tightly regulated 3.3V output. Two key features set
this device apart from similar, low-voltage step-down
switching regulators: high operating frequency and all
N-channel construction in the application circuit. The
300kHz operating frequency results in very small, low-
cost external surface-mount components.
The inductor, at 3.3µH for 5A, is physically at least five
times smaller than inductors found in competing solu-
tions. All N-channel construction and synchronous rectifi-
cation result in reduced cost and highest efficiency.
Efficiency exceeds 90% over a wide range of loading,
eliminating the need for heatsinking. Output capacitance
requirements are low, reducing board space and cost.
The MAX767 is a monolithic BiCMOS IC available in
20-pin SSOP packages. For other fixed output voltages
and package options, please consult the factory.
________________________Applications
Local 5V-to-3.3V DC-DC Conversion
Microprocessor Daughterboards
Power Supplies up to 10A or More
____________________________Features
o
>90% Efficiency
o
700µA Quiescent Supply Current
o
120µA Standby Supply Current
o
4.5V-to-5.5V Input Range
o
Low-Cost Application Circuit
o
All N-Channel Switches
o
Small External Components
o
Tiny Shrink-Small-Outline Package (SSOP)
o
Predesigned Applications:
Standard 5V to 3.3V DC-DC Converters up to 10A
High-Accuracy Pentium P54C VR-Spec Supply
o
Fixed Output Voltages Available:
3.3V (Standard)
3.45V (High-Speed PentiumTM)
3.6V (PowerPCTM)
______________Ordering Information
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
________________________________________________________________
Maxim Integrated Products
1
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
FB
DH
LX
BST
GND
ON
SS
CS
TOP VIEW
MAX767
DL
V
CC
V
CC
PGND
REF
GND
GND
GND
N.C.
GND
V
CC
SYNC
SSOP
__________________Pin Configuration
OUTPUT
3.3V
AT 5A
INPUT
4.5V TO 5.5V
LX
DL
GND
MAX767
V
CC
REF
3.3
µ
H
BST
DH
PGND
CS
FB
ON
________Typical Application Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0224; Rev 2; 8/94
Evaluation Kit Manual
Follows Data Sheet
PART
TEMP. RANGE
PIN-
PACKAGE
MAX767CAP
0°C to +70°C
20 SSOP
MAX767RCAP
0°C to +70°C
20 SSOP
MAX767SCAP
0°C to +70°C
20 SSOP
TM Pentium is a trademark of Intel.
PowerPC is a trademark of IBM.
MAX767C/D
0°C to +70°C
Dice*
REF.
TOL.
±1.8%
±1.8%
±1.8%
Ordering Information continued at end of data sheet.
*
Contact factory for dice specifications.
V
OUT
3.3V
3.45V
3.6V
MAX767TCAP
0°C to +70°C
20 SSOP
±1.2% 3.3V
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
V
CC
to GND .................................................................-0.3V, +7V
PGND to GND ........................................................................
±
2V
BST to GND ...............................................................-0.3V, +15V
LX to BST.....................................................................-7V, +0.3V
Inputs/Outputs to GND
(ON, REF, SYNC, CS, FB, SS) .....................-0.3V, V
CC
+ 0.3V
DL to PGND .....................................................-0.3V, V
CC
+ 0.3V
DH to LX...........................................................-0.3V, BST + 0.3V
REF Short to GND.......................................................Momentary
REF Current.........................................................................20mA
Continuous Power Dissipation (T
A
= +70°C)
20-Pin SSOP (derate 8.00mW/°C above +70°C) ..........640mW
Operating Temperature Ranges:
MAX767CAP/MAX767_CAP.................................0°C to +70°C
MAX767EAP/MAX767_EAP ..............................-40°C to +85°C
Lead Temperature (soldering, 10sec) .............................+300°C
PARAMETER
Oscillator Frequency
DH Sink/Source Current
MIN
TYP
MAX
1
260
300
340
UNITS
SS Source Current
A
2.50
4
6.5
(BST - LX) = 4.5V, DH = 2V
DL On Resistance
µA
Current-Limit Voltage
200
7
80
100
120
mV
V
CC
Fault Lockout Voltage
3.80
4.20
kHz
V
Line Regulation
High or low
0.1
%
Oscillator SYNC Range
SS Fault Sink Current
DH On Resistance
2
mA
7
3.24
3.30
3.36
240
350
kHz
SYNC High Pulse Width
V
CC
Standby Current
High or low, (BST - LX) = 4.5V
120
200
200
µA
V
CC
Quiescent Current
ns
0.7
1.0
mA
SYNC Low Pulse Width
200
ns
SYNC Rise/Fall Time
Output Voltage (FB)
200
ns
Oscillator Maximum Duty Cycle
V
CC
Input Supply Range
89
92
4.5
5.5
V
95
%
Input Low Voltage
3.17
3.35
3.46
V
0.8
V
Input High Voltage
2.40
3.32
3.50
3.60
V
CC
- 0.5
V
Input Current
±1
µA
DL Sink/Source Current
1
A
CONDITIONS
SYNC = 3.3V
SYNC = 0V or 5V
CS - FB
Falling edge, hysteresis = 1%
V
CC
= 4.5V to 5.5V
MAX767, MAX767R, MAX767S
ON = 0V, V
CC
= 5.5V
FB = CS = 3.5V
Not tested
SYNC = 3.3V
SYNC = 0V
SYNC, ON
ON
0mV < (CS - FB) < 80mV,
4.5V < V
CC
< 5.5V
(includes load and
line regulation)
SYNC
SYNC, ON = 0V or 5V
DL = 2V
Load Regulation
2.5
%
(CS - FB) = 0mV to 80mV
3.46
3.65
3.75
MAX767R
MAX767S
MAX767, MAX767T
ELECTRICAL CHARACTERISTICS
(V
CC
= ON = 5V, GND = PGND = SYNC = 0V, I
REF
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
Reference Voltage (REF)
3.26
3.30
3.34
V
MAX767T
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
_______________________________________________________________________________________
3
100
50
0.001
0.1
10
EFFICIENCY vs. OUTPUT CURRENT
(1.5A CIRCUIT)
60
MAX767-01
OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
0.01
1
100
50
0.001
0.1
10
EFFICIENCY vs. OUTPUT CURRENT
(3A CIRCUIT)
60
MAX767-02
OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
0.01
1
100
50
0.001
0.1
10
EFFICIENCY vs. OUTPUT CURRENT
(5A CIRCUIT)
60
MAX767-03
OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
0.01
1
100
50
0.001
0.1
10
EFFICIENCY vs. OUTPUT CURRENT
(7A CIRCUIT)
60
MAX767-04
OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
0.01
1
IDLE-MODE WAVEFORMS
I
LOAD
= 300mA
3.3V OUTPUT
50mV/div, AC COUPLED
LX
5V/div
5µs/div
100
50
0.001
0.1
10
EFFICIENCY vs. OUTPUT CURRENT
(10A CIRCUIT)
60
MAX767-05
OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
0.01
1
1000
0.01
0.001
1
100
SWITCHING FREQUENCY vs.
PERCENT OF FULL LOAD
0.1
MAX767-06
LOAD CURRENT (% FULL LOAD)
SWITCHING FREQUENCY (kHz)
1
10
100
0.01
0.1
10
SYNC = REF (300kHz)
PWM-MODE WAVEFORMS
I
LOAD
= 5A
3.3V OUTPUT
50mV/div, AC COUPLED
LX
5V/div
1µs/div
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1 (5A configuration), V
IN
= 5V, oscillator frequency = 300kHz, T
A
= +25°C, unless otherwise noted.)
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
4
_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1 (5A configuration), V
IN
= 5V, oscillator frequency = 300kHz, T
A
= +25°C, unless otherwise noted.)
1.5A CIRCUIT LOAD-TRANSIENT RESPONSE
200µs/div
1.5A
3.3V OUTPUT
50mV/div
AC-COUPLED
0A
LOAD CURRENT
3A CIRCUIT LOAD-TRANSIENT RESPONSE
200µs/div
3A
3.3V OUTPUT
50mV/div
AC-COUPLED
0A
LOAD CURRENT
5A CIRCUIT LOAD-TRANSIENT RESPONSE
200µs/div
5A
3.3V OUTPUT
50mV/div
AC-COUPLED
0A
LOAD CURRENT
10A CIRCUIT LOAD-TRANSIENT RESPONSE
200µs/div
10A
3.3V OUTPUT
50mV/div
AC-COUPLED
0A
LOAD CURRENT
7A CIRCUIT LOAD-TRANSIENT RESPONSE
200µs/div
7A
3.3V OUTPUT
50mV/div
AC-COUPLED
0A
LOAD CURRENT
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
_______________________________________________________________________________________
5
______________________________________________________________Pin Description
16
NAME
FUNCTION
1
CS
Current-sense input: +100mV = nominal current-limit level referred to FB.
2
SS
Soft-start input. Ramp time to full current limit is 1ms/nF of capacitance to GND.
3
ON
ON/O
--
F
--
F
control input to disable the PWM. Tie directly to V
CC
for automatic start-up.
PIN
DL
Gate-drive output for the low-side synchronous rectifier MOSFET
47, 11
GND
Low-current analog ground. Feedback reference point for the output.
8
REF
3.3V internal reference output. Bypass to GND with 0.22µF minimum capacitor.
9
SYNC
Oscillator control/synchronization input. Connect to V
CC
or GND for 200kHz; connect to REF for
300kHz. For external clock synchronization in the 240kHz to 350kHz range, a high-to-low transition
causes a new cycle to start.
10, 14, 15
V
CC
Supply voltage input: 4.5V to 5.5V
17
BST
Boost capacitor connection (0.1µF)
12
N.C.
No internal connection
13
PGND
Power ground
18
LX
Inductor connection. Can swing 2V below GND without latchup.
19
DH
Gate-drive output for the high-side MOSFET
20
FB
Feedback and current-sense input for the PWM
OUTPUT
3.3V
LX
DL
GND
SS
MAX767
ON
VCC
REF
L1
BST
DH
D2
PGND
CS
FB
SHUTDOWN
ON/OFF
N1
N2
D1
SMALL-
SIGNAL
SCHOTTKY
C1
R1
C3
0.1
µ
F
C2
C6
0.22
µ
F
C5
(OPTIONAL)
SYNC
R2
10
INPUT
4.5V TO 5.5V
0.01
µ
F
C4
4.7
µ
F
Figure 1. Standard Application Circuit
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