Maxim MAX767TCAP, MAX767RCAP, MAX767REAP, MAX767SCAP, MAX767SEAP Datasheet

19-0224; Rev 2; 8/94

Evaluation Kit Manual

Follows Data Sheet

5V-to-3.3V, Synchronous, Step-Down

_______________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, low­cost external surface-mount components.

The inductor, at 3.3µH for 5A, is physically at least five
times smaller than inductors found in competing solu­tions. All N-channel construction and synchronous rectifi­cation 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

________Typical Application Circuit

Power-Supply Controller

____________________________Features

♦ >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

♦ Fixed Output Voltages Available:

3.3V (Standard)

3.45V (High-Speed Pentium™)

3.6V (PowerPC™)

______________Ordering Information

PART TEMP. RANGE

MAX767CAP 0°C to +70°C 20 SSOP
MAX767RCAP 0°C to +70°C 20 SSOP
MAX767SCAP 0°C to +70°C 20 SSOP
MAX767TCAP 0°C to +70°C 20 SSOP ±1.2% 3.3V
MAX767C/D 0°C to +70°C Dice*

Ordering Information continued at end of data sheet.

*

Contact factory for dice specifications.

PIN-

PACKAGE

REF.
TOL.

±1.8%
±1.8%
±1.8%

–

V

OUT

3.3V

3.45V

3.6V

–

MAX767

INPUT

4.5V TO 5.5V

V

ON

CC

MAX767

REF

™ Pentium is a trademark of Intel. PowerPC is a trademark of IBM.

BST

DH

LX

DL

PGND

CS

FB

GND

________________________________________________________________

3.3µH

OUTPUT

3.3V

AT 5A

__________________Pin Configuration

TOP VIEW

CS

1

SS

2

ON

3

GND
GND
GND

GND

REF

SYNC

V

CC

MAX767

4
5
6
7
8
9

10

SSOP

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

FB

20

DH

19

LX

18

BST

17

DL

16

V

15

CC

V

14

CC

PGND

13

N.C.

12

GND

11

1

5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller

ABSOLUTE MAXIMUM RATINGS

VCCto 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

DL to PGND .....................................................-0.3V, V

MAX767

DH to LX...........................................................-0.3V, BST + 0.3V

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.

CC
CC

+ 0.3V
+ 0.3V

ELECTRICAL CHARACTERISTICS

(VCC= ON = 5V, GND = PGND = SYNC = 0V, I

PARAMETER

VCCInput Supply Range

0mV < (CS - FB) < 80mV,

Output Voltage (FB)

Load Regulation 2.5 %(CS - FB) = 0mV to 80mV
Line Regulation
VCCFault Lockout Voltage
Current-Limit Voltage
SS Source Current
SS Fault Sink Current

Reference Voltage (REF)
VCCStandby Current

VCCQuiescent Current
Oscillator Frequency
Oscillator SYNC Range

SYNC High Pulse Width
SYNC Low Pulse Width 200 ns
SYNC Rise/Fall Time

Oscillator Maximum Duty Cycle
Input Low Voltage
Input High Voltage
Input Current ±1 µA

DL Sink/Source Current 1 A
DH Sink/Source Current
DL On Resistance
DH On Resistance

4.5V < V
(includes load and
line regulation)

VCC= 4.5V to 5.5V
Falling edge, hysteresis = 1%
CS - FB

MAX767, MAX767R, MAX767S
MAX767T
ON = 0V, VCC= 5.5V
FB = CS = 3.5V
SYNC = 3.3V
SYNC = 0V or 5V

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

CC

REF

< 5.5V

= 0mA, TA= T

CONDITIONS

REF Short to GND.......................................................Momentary

REF Current.........................................................................20mA

Continuous Power Dissipation (TA= +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

to T

MIN

MAX767, MAX767T
MAX767R
MAX767S

, unless otherwise noted. Typical values are at TA= +25°C.)

MAX

MIN TYP MAX

4.5 5.5 V

3.17 3.35 3.46

3.32 3.50 3.60

3.46 3.65 3.75

0.1 %

3.80 4.20
80 100 120 mV

2.50 4 6.5

2 mA

3.24 3.30 3.36

3.26 3.30 3.34

120 200

0.7 1.0 mA

260 300 340

200
240 350 kHz
200

89 92

95

2.40

V

- 0.5

CC

1

UNITS

200 ns

0.8 V

7
7

V

V

µA

V

µA

kHz

ns

%

V

A

Ω
Ω

2 _______________________________________________________________________________________

5V-to-3.3V, Synchronous, Step-Down

Power-Supply Controller

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1 (5A configuration), VIN= 5V, oscillator frequency = 300kHz, TA= +25°C, unless otherwise noted.)

EFFICIENCY vs. OUTPUT CURRENT

(1.5A CIRCUIT)

100

90

80

70

EFFICIENCY (%)

60

50

0.001 0.1 10

0.01 1
OUTPUT CURRENT (A)

EFFICIENCY vs. OUTPUT CURRENT

(7A CIRCUIT)

100

90

MAX767-01

EFFICIENCY (%)

MAX767-04

EFFICIENCY vs. OUTPUT CURRENT

(3A CIRCUIT)

100

90

80

70

60

50

0.001 0.1 10

0.01 1
OUTPUT CURRENT (A)

EFFICIENCY vs. OUTPUT CURRENT

(10A CIRCUIT)

100

90

100

MAX767-02

EFFICIENCY (%)

1000

MAX767-05

100

EFFICIENCY vs. OUTPUT CURRENT

(5A CIRCUIT)

90

80

70

60

50

0.001 0.1 10

0.01 1
OUTPUT CURRENT (A)

SWITCHING FREQUENCY vs.

PERCENT OF FULL LOAD

SYNC = REF (300kHz)

MAX767

MAX767-03

MAX767-06

80

70

EFFICIENCY (%)

60

50

0.001 0.1 10

0.01 1
OUTPUT CURRENT (A)

IDLE-MODE WAVEFORMS



= 300mA

I

LOAD

5µs/div

80

70

EFFICIENCY (%)

60

50

0.001 0.1 10

0.01 1
OUTPUT CURRENT (A)

3.3V OUTPUT
50mV/div, AC COUPLED

LX
5V/div

I

LOAD

10

1

0.1

SWITCHING FREQUENCY (kHz)

0.01

0.001 1 100

PWM-MODE WAVEFORMS

= 5A

1µs/div

0.01 0.1 10

LOAD CURRENT (% FULL LOAD)

3.3V OUTPUT
50mV/div, AC COUPLED

LX
5V/div



_______________________________________________________________________________________

3

5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 1 (5A configuration), VIN= 5V, oscillator frequency = 300kHz, TA= +25°C, unless otherwise noted.)

1.5A CIRCUIT LOAD-TRANSIENT RESPONSE

MAX767

5A CIRCUIT LOAD-TRANSIENT RESPONSE

200µs/div

1.5A
LOAD CURRENT

0A

3.3V OUTPUT

50mV/div
AC-COUPLED

5A

LOAD CURRENT

0A

3.3V OUTPUT

50mV/div
AC-COUPLED

3A CIRCUIT LOAD-TRANSIENT RESPONSE

3A

LOAD CURRENT

0A

3.3V OUTPUT
50mV/div
AC-COUPLED

200µs/div

7A CIRCUIT LOAD-TRANSIENT RESPONSE

7A

LOAD CURRENT

0A

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

1

2 SS Soft-start input. Ramp time to full current limit is 1ms/nF of capacitance to GND.
3 ON

4–7, 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

10, 14, 15 V

12 N.C. No internal connection
13 PGND Power ground
16
17 BST Boost capacitor connection (0.1µF)
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

NAME FUNCTION

CS Current-sense input: +100mV = nominal current-limit level referred to FB.

ON/O—F—F–control input to disable the PWM. Tie directly to VCCfor automatic start-up.

Oscillator control/synchronization input. Connect to VCCor 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.

CC

Supply voltage input: 4.5V to 5.5V

DL Gate-drive output for the low-side synchronous rectifier MOSFET

MAX767

SHUTDOWN

ON/OFF

C5

(OPTIONAL)

C6

0.22µF

Figure 1. Standard Application Circuit

0.01µF

4.7µF

C4

ON

SS

SYNC

REF

V

CC

MAX767

GND

R2

10Ω

BST

PGND

INPUT

4.5V TO 5.5V

D1
SMALL-
SIGNAL 
SCHOTTKY

DH

LX

DL

CS

FB

C3

N1

0.1µF

D2

N2

C1

OUTPUT

L1

R1

3.3V

C2

_______________________________________________________________________________________ 5

5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller

_____Standard Application Circuits

This data sheet shows five predesigned circuits with
output current capabilities from 1.5A to 10A. Many
users will find one of these standard circuits appropri­ate for their needs. If a standard circuit is used, the
remainder of this data sheet (

Applications Information and Design Procedure

MAX767

be bypassed.
Figure 1 shows the Standard Application Circuit. Table 1

gives component values and part numbers for five dif­ferent implementations of this circuit: 1.5A, 3A, 5A, 7A,
and 10A output currents.

Each of these circuits is designed to deliver the full
rated output load current over the temperature range
listed. In addition, each will withstand a short circuit of
several seconds duration from the output to ground. If
the circuit must withstand a continuous short circuit,
refer to the
required changes.

Good layout is necessary to achieve the designed out­put power, high efficiency, and low noise. Good layout
includes the use of a ground plane, appropriate com­ponent placement, and correct routing of traces using
appropriate trace widths. The following points are in
order of decreasing importance.

1. A ground plane is essential for optimum perfor­mance. In most applications, the circuit will be
located on a multilayer board and full use of the four
or more copper layers is recommended. Use the
top and bottom layers for interconnections and the
inner layers for an uninterrupted ground plane.

2. Because the sense resistance values are similar to
a few centimeters of narrow traces on a printed cir­cuit board, trace resistance can contribute signifi­cant errors. To prevent this, Kelvin connect CS and
FB to the sense resistor; i.e., use separate traces
not carrying any of the inductor or load current, as
shown in Figure 2. These signals must be carefully
shielded from DH, DL, BST, and the LX node.

Important: place the sense resistor as close as pos­sible to and no further than 10mm from the MAX767.

3. Place the LX node components N1, N2, L1, and D2
as close together as possible. This reduces resis­tive and switching losses and confines noise due to
ground inductance.

4. The input filter capacitor C1 should be less than
10mm away from N1’s drain. The connecting cop­per trace carries large currents and must be at least
2mm wide, preferably 5mm.

Short-Circuit Duration

Detailed Description

section for the

Layout and Grounding

and

) can

5. Keep the gate connections to the MOSFETs short
for low inductance (less than 20mm long and more
than 0.5mm wide) to ensure clean switching.

6. To achieve good shielding, it is best to keep all
switching signals (MOSFET gate drives DH and DL,
BST, and the LX node) on one side of the board
and all sensitive nodes (CS, FB, and REF) on the
other side.

7. Connect the GND and PGND pins directly to the
ground plane, which should ideally be an inner
layer of a multilayer board.

_______________Detailed Description

Note:

The remainder of this document contains the
detailed information necessary to design a circuit that
differs substantially from the five standard application
circuits. If you are using one of the predesigned stan­dard circuits, the following sections are provided only
for your reading pleasure.

The MAX767 converts a 4.5V to 5.5V input to a 3.3V
output. Its load capability depends on external compo­nents and can exceed 10A. The 3.3V output is generat­ed by a current-mode, pulse-width-modulation (PWM)
step-down regulator. The PWM regulator operates at
either 200kHz or 300kHz, with a corresponding trade­off between somewhat higher efficiency (200kHz) and
smaller external component size (300kHz). The
MAX767 also has a 3.3V, 5mA reference voltage. Fault­protection circuitry shuts off the output should the refer­ence lose regulation or the input voltage go below 4V
(nominally).

External components for the MAX767 include two N­channel MOSFETs, a rectifier, and an LC output filter.
The gate-drive signal for the high-side MOSFET, which
must exceed the input voltage, is provided by a boost
circuit that uses a 0.1µF capacitor. The synchronous
rectifier keeps efficiency high by clamping the voltage
across the rectifier diode. An external low-value cur­rent-sense resistor sets the maximum current limit, pre­venting excessive inductor current during start-up or
under short-circuit conditions. An optional external
capacitor sets the programmable soft-start, reducing
in-rush surge currents upon start-up and providing
adjustable power-up time.

The PWM regulator is a direct-summing type, lacking a
traditional integrator-type error amplifier and the phase
shift associated with it. It therefore does not require
external feedback-compensation components, as long
as you follow the ESR guidelines in the

Information and Design Procedure

sections.

Applications

6 _______________________________________________________________________________________