19-0224; Rev 3; 7/00
NUAL
KIT MA
ATION
ET
EVALU
TA SHE
WS DA
FOLLO
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
____________________________Features
o
o
o
o
o
o
o
o
o
>90% Efficiency
700µA Quiescent Supply Current
120µA Standby Supply Current
4.5V-to-5.5V Input Range
Low-Cost Application Circuit
All N-Channel Switches
Small External Components
Tiny Shrink-Small-Outline Package (SSOP)
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 Pentium™)
3.6V (PowerPC™)
________________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.
MAX767
_______________Ordering Information
PART
MAX767CAP
MAX767RCAP
MAX767SCAP
MAX767TCAP
MAX767C/D
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
PIN-
PACKAGE
20 SSOP
20 SSOP
20 SSOP
20 SSOP
Dice*
REF
TOL
V
OUT
(V)
________________________Applications
Local 5V-to-3.3V DC-DC Conversion
Microprocessor Daughterboards
Power Supplies up to 10A or More
±1.8% 3.3
±1.8% 3.45
±1.8% 3.6
±1.2% 3.3
—
—
_________Typical Application Circuit
INPUT
4.5V TO 5.5V
Ordering Information continued at end of data sheet.
*
Contact factory for dice specifications.
__________________Pin Configuration
TOP VIEW
V
CC
ON
BST
DH
OUTPUT
3.3V
AT 5A
CS
1
SS
2
ON
3
GND
4
DL
GND
5
GND
6
GND
7
REF
8
SYNC
9
V
CC
10
20
FB
19
DH
18
LX
3.3µH
MAX767
LX
MAX767
17
BST
16
DL
15
V
CC
14
V
CC
13
PGND
12
N.C.
11
GND
PGND
CS
FB
REF
GND
SSOP
Pentium is a trademark of Intel. PowerPC is a trademark of IBM.
________________________________________________________________
Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
MAX767
ABSOLUTE MAXIMUM RATINGS
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, 10s) .................................+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
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.)
PARAMETER
V
CC
Input Supply Range
Output Voltage (FB)
Load Regulation
Line Regulation
V
CC
Fault Lockout Voltage
Current-Limit Voltage
SS Source Current
SS Fault Sink Current
Reference Voltage (REF)
V
CC
Standby Current
V
CC
Quiescent Current
Oscillator Frequency
Oscillator SYNC Range
SYNC High Pulse Width
SYNC Low Pulse Width
SYNC Rise/Fall Time
Oscillator Maximum Duty Cycle
Input Low Voltage
Input High Voltage
Input Current
DL Sink/Source Current
DH Sink/Source Current
DL On Resistance
DH On Resistance
Not tested
SYNC = 3.3V
SYNC = 0V
SYNC, ON
ON
SYNC
SYNC, ON = 0V or 5V
DL = 2V
(BST - LX) = 4.5V, DH = 2V
High or low
High or low, (BST - LX) = 4.5V
1
1
7
7
2.40
V
CC
- 0.5
±1
89
92
95
0.8
MAX767, MAX767R, MAX767S
MAX767T
ON = 0V, V
CC
= 5.5V
FB = CS = 3.5V
SYNC = 3.3V
SYNC = 0V or 5V
260
240
200
200
200
CONDITIONS
0mV < (CS - FB) < 80mV, MAX767, MAX767T
4.5V < V
CC
< 5.5V
MAX767R
(includes load and
MAX767S
line regulation)
(CS - FB) = 0mV to 80mV
V
CC
= 4.5V to 5.5V
Falling edge, hysteresis = 1%
CS - FB
3.80
80
2.50
2
3.24
3.26
3.30
3.30
120
0.7
300
200
3.36
3.34
200
1.0
340
350
100
4
MIN
4.5
3.17
3.32
3.46
TYP
3.35
3.50
3.65
2.5
0.1
4.20
120
6.5
MAX
5.5
3.46
3.60
3.75
%
%
V
mV
µA
mA
V
µA
mA
kHz
kHz
ns
ns
ns
%
V
V
µA
A
A
Ω
Ω
V
UNITS
V
2
_______________________________________________________________________________________
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1 (5A configuration), V
IN
= 5V, oscillator frequency = 300kHz, T
A
= +25°C, unless otherwise noted.)
MAX767
EFFICIENCY vs. OUTPUT CURRENT
(1.5A CIRCUIT)
MAX767-01
EFFICIENCY vs. OUTPUT CURRENT
(3A CIRCUIT)
MAX767-02
EFFICIENCY vs. OUTPUT CURRENT
(5A CIRCUIT)
MAX767-03
100
100
100
90
EFFICIENCY (%)
EFFICIENCY (%)
90
EFFICIENCY (%)
0.001
0.1
10
90
80
80
80
70
70
70
60
60
60
50
0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
50
0.01
1
OUTPUT CURRENT (A)
50
0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
(7A CIRCUIT)
MAX767-04
EFFICIENCY vs. OUTPUT CURRENT
(10A CIRCUIT)
MAX767-05
SWITCHING FREQUENCY vs.
PERCENT OF FULL LOAD
MAX767-06
100
100
1000
SWITCHING FREQUENCY (kHz)
SYNC = REF (300kHz)
100
90
EFFICIENCY (%)
EFFICIENCY (%)
90
80
80
10
70
70
1
60
60
0.1
50
0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
50
0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
0.01
0.001
0.01
0.1
1
10
100
LOAD CURRENT (% FULL LOAD)
IDLE-MODE WAVEFORMS
3.3V OUTPUT
50mV/div, AC COUPLED
PWM-MODE WAVEFORMS
3.3V OUTPUT
50mV/div, AC COUPLED
LX
5V/div
LX
5V/div
5µs/div
I
LOAD
= 300mA
I
LOAD
= 5A
1µs/div
_______________________________________________________________________________________
3
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
MAX767
_____________________________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
3A CIRCUIT LOAD-TRANSIENT RESPONSE
1.5A
LOAD CURRENT
0A
3A
LOAD CURRENT
0A
3.3V OUTPUT
50mV/div
AC-COUPLED
3.3V OUTPUT
50mV/div
AC-COUPLED
200µs/div
200µs/div
5A CIRCUIT LOAD-TRANSIENT RESPONSE
7A CIRCUIT LOAD-TRANSIENT RESPONSE
5A
LOAD CURRENT
0A
7A
LOAD CURRENT
0A
3.3V OUTPUT
50mV/div
AC-COUPLED
3.3V OUTPUT
50mV/div
AC-COUPLED
200µs/div
200µs/div
10A CIRCUIT LOAD-TRANSIENT RESPONSE
10A
LOAD CURRENT
0A
3.3V OUTPUT
50mV/div
AC-COUPLED
200µs/div
4
_______________________________________________________________________________________
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
______________________________________________________________Pin Description
PIN
NAME
CS
SS
ON
GND
REF
SYNC
V
CC
N.C.
PGND
DL
BST
LX
DH
FB
FUNCTION
Current-sense input: +100mV = nominal current-limit level referred to FB.
Soft-start input. Ramp time to full current limit is 1ms/nF of capacitance to GND.
—–
—
ON/OFF control input to disable the PWM. Tie directly to V
CC
for automatic start-up.
Low-current analog ground. Feedback reference point for the output.
3.3V internal reference output. Bypass to GND with 0.22µF minimum capacitor.
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.
Supply voltage input: 4.5V to 5.5V
No internal connection
Power ground
Gate-drive output for the low-side synchronous rectifier MOSFET
Boost capacitor connection (0.1µF)
Inductor connection. Can swing 2V below GND without latchup.
Gate-drive output for the high-side MOSFET
Feedback and current-sense input for the PWM
INPUT
4.5V TO 5.5V
MAX767
1
2
3
4–7, 11
8
9
10, 14, 15
12
13
16
17
18
19
20
R2
C4
4.7µF
10Ω
D1
SMALL-
SIGNAL
SCHOTTKY
BST
DH
C3
0.1µF
L1
C1
SHUTDOWN
ON/OFF
ON
VCC
N1
R1
OUTPUT
3.3V
MAX767
0.01µF
C5
(OPTIONAL)
SS
LX
D2
DL
PGND
N2
C2
SYNC
CS
REF
GND
C6
0.22µF
FB
Figure 1. Standard Application Circuit
_______________________________________________________________________________________
5
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