MAX1605
30V Internal Switch LCD Bias Supply
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 SHDN
Active-Low Shutdown Input. A logic low shuts down the device and reduces the supply current
to 0.1µA. Connect SHDN to V
CC
for normal operation.
2V
CC
IC Supply Voltage (+2.4V to +5.5V). Bypass V
CC
to GND with a 0.1µF or greater capacitor.
3 GND Ground
4LX
Inductor Connection. The drain of an internal 30V N-channel MOSFET. LX is high impedance in
shutdown.
5 LIM
Inductor Current Limit Selection. Connect LIM to V
CC
for 500mA, leave LIM floating for 250mA,
or connect LIM to GND for 125mA.
6FB
Feedback Input. Connect to a resistive-divider network between the output (V
OUT
) and FB to set
the output voltage between V
IN
and 30V. The feedback threshold is 1.25V.
Detailed Description
The MAX1605 compact, step-up DC-DC converter oper-
ates from a +2.4V to +5.5V supply. Consuming only
18µA of supply current, the device includes an internal
switching MOSFET with 1Ω on-resistance and selectable
current limit (Figure 1). During startup, the MAX1605
extends the minimum off-time, limiting initial surge cur-
rent. The MAX1605 also features a shutdown mode.
Control Scheme
The MAX1605 features a minimum off-time, current-lim-
ited control scheme. The duty cycle is governed by a
pair of one-shots that set a minimum off-time and a
maximum on-time. The switching frequency can be up
to 500kHz and depends upon the load and input volt-
age. The peak current limit of the internal N-channel
MOSFET is pin selectable and may be set at 125mA,
250mA, or 500mA (Figure 2).
