MAX1605 Datasheet, PDF (6/12 Pages) Maxim Integrated Products – 30V Internal Switch LCD Bias Supply

30V Internal Switch LCD Bias Supply
PIN
NAME
1
SHDN
2
V_CC
3
GND
4
LX
5
LIM
6
FB
V_IN = 0.8V TO V_OUT
Pin Description
FUNCTION
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.
IC Supply Voltage (+2.4V to +5.5V). Bypass V_CC to GND with a 0.1µF or greater capacitor.
Ground
Inductor Connection. The drain of an internal 30V N-channel MOSFET. LX is high impedance in
shutdown.
Inductor Current Limit Selection. Connect LIM to V_CC for 500mA, leave LIM floating for 250mA,
or connect LIM to GND for 125mA.
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.
L1
10µH
V_CC = 2.4V TO 5.5V
V_CC
LIM
CONTROL
LOGIC
CURRENT
LIMIT
LX
N
V_OUT = V_IN TO 30V
C_FF
C_OUT
SHUTDOWN
LOGIC
ON
OFF
SHDN
MAX1605
ERROR
AMPLIFIER
1.25V
R1
FB
R2
GND
Figure 1. Functional Diagram
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).
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