User Manual

MAX1649/MAX1651
5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers
_______________________________________________________________________________________ 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
V
OUT
at 3.3V, typical no-load supply current for the
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
QS
R
FROM V+
FROM V+
CS
EXT
OUT
GND
REF
SHDN
FBV+
1.5V
REFERENCE
F/F
N
™ Dual-Mode is a trademark of Maxim Integrated Products
50mV
Figure 2. Block Diagram