5V/3.3V or Adjustable, High-Efficiency,

Low-Dropout, Step-Down DC-DC Controllers

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7

Shutdown Mode

When SHDN is high, the MAX1649/MAX1651 enter shut-

down mode. In this mode, the internal biasing circuitry is

turned off (including the reference) and the supply cur-

rent drops to less than 5µA. EXT goes high, turning off the

external MOSFET. SHDN is a logic-level input. Connect

SHDN to GND for normal operation.

Quiescent Current

In normal operation, the device's typical quiescent cur-

rent is 78µA. In an actual application, even with no load,

additional current is drawn to supply external feedback

resistors (if used) and the diode and capacitor leakage

currents. In the circuit of Figure 1, with V+ at 5V and

entire circuit is 90µA.

MAX1649

MAX1651

Q

MINIMUM

OFF-TIME

ONE-SHOT

TRIG

Q

MAXIMUM

ON-TIME

ONE-SHOT

TRIG

DUAL-MODE™

COMPARATOR

ERROR

COMPARATOR

CURRENT

COMPARATOR

110mV

Q

S

R

FROM V+

FROM V+

CS

EXT

OUT

GND

REF

SHDN

FB

V+

1.5V

REFERENCE

F/F

N

™ Dual-Mode is a trademark of Maxim Integrated Products

50mV

Figure 2. Block Diagram