Datasheet

MAX1749
SOT23 Vibrator Motor Driver
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Detailed Description
The MAX1749 is a low-quiescent-current, vibrator motor dri-
ver designed for battery-powered wireless handsets and
pagers. The device supplies an adjustable +1.25V to +6.5V
output for load currents up to 120mA. The MAX1749 allows
for a constant vibration force while operating from a +2.5V
to +6.5V input voltage range.
The 1.25V bandgap reference is connected to the error
amplifier’s inverting input. The error amplifier compares this
reference with the feedback voltage and amplifies the differ-
ence. The MOSFET driver reads the error signal and
applies the appropriate drive to the p-channel pass transis-
tor. If the feedback voltage is lower than the reference volt-
age, the pass-transistor gate is pulled lower than the
reference, allowing more current to flow and increasing the
output voltage. If the feedback voltage is too high, the pass-
transistor gate is pulled-up, allowing less current to flow to
the output. The output voltage is fed back to SET either
directly for a 1.25V fixed output or through an external resis-
tor-divider for an adjustable +1.25V to V
IN
output. Additional
blocks include a current limiter, reverse battery protection, a
thermal sensor, and ON/ OFF logic.
Internal P-Channel Pass Transistor
The MAX1749 features a 1.1Ω typical P-channel MOS-
FET pass transistor. This provides several advantages
over similar designs using PNP pass transistors, includ-
ing longer battery life.
ON/OFF
LOGIC
ERROR
AMP
1.25V
REF
P
OUT
SET
GND
IN
ON
MAX1749
MOS DRIVER
WITH I
LIMIT
THERMAL
SENSOR
REVERSE
BATTERY
PROTECTION
______________________________________________________________Pin Description
Active-High On/Off Input. Apply a logic high to deliver power to the load. Apply a logic low to disconnect the
load and reduce the supply current to 0.1nA.
ON1
PIN FUNCTIONNAME
GND2
Ground. This pin also functions as a heatsink. Solder to large pads or the circuit board ground plane to max-
imize thermal dissipation.
3
Regulator Input. Supply voltage can range from +2.5V to +6.5V. Bypass with 1µF to GND (see Capacitor
Selection and Regulator Stability ).
OUT4
Regulator Output. Fixed 1.25V or adjustable from 1.25V to V
IN
. Sources up to 120mA. Bypass with a 1µF,
<0.2Ω typical ESR capacitor to GND.
IN
SET5
Feedback Input for Setting the Output Voltage. Connect to OUT for 1.25V regulated output (see Output
Voltage Selection ). Connect to an external resistor-divider for adjustable-output operation.
Figure 1. Functional Diagram