MAX764CSA-T Maxim Integrated Products, MAX764CSA-T Datasheet - Page 8

• Manufacturer Part Number: MAX764CSA-T
• Description: DC/DC Switching Regulators 5/12/15/AdjV DC/DC Inverter
• Manufacturer: Maxim Integrated Products

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:
-5V/-12V/-15V or Adjustable,
High-Efficiency, Low I
Figure 1. Block Diagram
8
_______________Detailed Description
SHDN
REF
_______________________________________________________________________________________
TRIG
COMPARATOR
ONE-SHOT
ERROR
Q
Operating Principle
Q
ONE-SHOT
TRIG
CONTROL CIRCUITS
FB
CURRENT
S
R
Q
Q
COMPARATOR
DC-DC Inverters
GND
COMPARATOR
1) They can operate with miniature (less than 5mm
2) The current-limited PFM control scheme allows efficien-
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 (V
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
CURRENT
diameter) surface-mount inductors, because of their
300kHz switching frequency.
cies exceeding 80% over a wide range of load currents.
N
REFERENCE
I
V
1.5V
OUT
FROM OUT
FROM V+
CURRENT)
MAX764
MAX765
MAX766
I
OUT
plus a diode drop (when the
(FULL
0.2V
). The principal benefit of
P
FROM V+
0.1V
(HALF
CURRENT)
OUT
V+
V+
LX