MAX764C データシートの表示（PDF） - Maxim Integrated

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MAX764C

-5V/-12V/-15V or Adjustable, High-Efficiency, Low IQ DC-DC Inverters

Maxim Integrated 

-5V/-12V/-15V or Adjustable,

High-Efficiency, Low IQ DC-DC Inverters

FB

COMPARATOR

REF

SHDN

ERROR

COMPARATOR

MAX764

MAX765

MAX766

OUT

N

TRIG

Q

ONE-SHOT

Q

TRIG

ONE-SHOT

S

Q

CURRENT

R

COMPARATOR

1.5V

REFERENCE

FROM V+

FROM OUT

V+

V+

P

LX

Figure 1. Block Diagram

CURRENT

CONTROL CIRCUITS

GND

0.2V

(FULL

CURRENT)

0.1V

(HALF

CURRENT)

FROM V+

_______________Detailed Description

Operating Principle

The MAX764/MAX765/MAX766 are BiCMOS, inverting,

switch-mode power supplies that provide fixed outputs

of -5V, -12V, and -15V, respectively; they can also be

set to any desired output voltage using an external

resistor divider. Their unique control scheme combines

the advantages of pulse-frequency modulation (pulse

skipping) and pulse-width modulation (continuous puls-

ing). The internal P-channel power MOSFET allows

peak currents of 0.75A, increasing the output current

capability over previous pulse-frequency-modulation

(PFM) devices. Figure 1 shows the MAX764/MAX765/

MAX766 block diagram.

The MAX764/MAX765/MAX766 offer three main

improvements over prior solutions:

1) They can operate with miniature (less than 5mm

diameter) surface-mount inductors, because of their

300kHz switching frequency.

2) The current-limited PFM control scheme allows efficien-

cies exceeding 80% over a wide range of load currents.

3) Maximum quiescent supply current is only 120µA.

Figures 2 and 3 show the standard application circuits

for these devices. In these configurations, the IC is

powered from the total differential voltage between the

input (V+) and output (VOUT). The principal benefit of

this arrangement is that it applies the largest available

signal to the gate of the internal P-channel power MOS-

FET. This increased gate drive lowers switch on-resis-

tance and increases DC-DC converter efficiency.

Since the voltage on the LX pin swings from V+ (when the

switch is ON) to IVOUTI plus a diode drop (when the

8 _______________________________________________________________________________________

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