MAX1578-MAX1579 Datasheet, PDF (7/13 Pages) Maxim Integrated Products – Complete Bias and White LED Power Supplies for Small TFT Displays

Complete Bias and White LED Power Supplies
for Small TFT Displays
Pin Description (continued)
PIN
NAME
FUNCTION
11
ONBIAS ^{Logic Input to Enable VDD, MAIN, POS, and NEG Charge Pumps. Drive ONBIAS high to enable all the}
charge pumps. Connect to GND to disable the charge pumps.
12
GND
Ground. Connect to PGND and the exposed pad directly under the IC.
13
COMP
LED Driver Compensation. Connect a 0.1µF from COMP to GND. C_COMP stabilizes the driver and
sets the soft-start time.
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED current. For the
14
CS
MAX1578, CS regulates to V_CTRL / 5 or 0.327V, whichever is lower. For the MAX1579, CS regulates to
V_CTRL / 5 or 0.340V, whichever is lower.
LED Brightness Control Input. Connect CTRL to a 0.24V to 1.65V input to set the brightness of the
15
CTRL
external LEDs. Hold CTRL below 100mV for more than 10.5ms, to shut down the LED driver. Drive CTRL
with a 200Hz to 200kHz unfiltered PWM dimming signal for DC LED current that is proportional to the
signal’s duty cycle.
16
OUT
Overvoltage Sense Input. The MAX1578/MAX1579 turn off the n-channel MOSFET when V_OUT exceeds 34V.
Once V_OUT drops below 32V, the IC re-enters soft-start. Bypass OUT to GND with a 0.1µF capacitor.
17
LX
Inductor Connection. Connect to the switched side of the external inductor as well as the anode of the
external diode. LX is high impedance during shutdown.
18
PGND Power Ground. Connect to GND and the exposed pad directly under the IC.
19
C1N
Main Charge-Pump Transfer Capacitor Negative Connection 1. Connect a 2.2µF capacitor between
C1N and C1P.
20
C2N
Main Charge-Pump Transfer Capacitor Negative Connection 2. Connect a 2.2µF capacitor between
C2N and C2P.
21
IN
Power-Supply Input. Connect to a 2.7V to 5.5V input supply. Bypass IN to GND with a 4.7µF capacitor.
22
C2P
Main Charge-Pump Transfer Capacitor Positive Connection 2. Connect a 2.2µF capacitor between
C2P and C2N.
23
C1P
Main Charge-Pump Transfer Capacitor Positive Connection 1. Connect a 2.2µF capacitor between
C1P and C1N.
24
V_DD
Regulated Main Charge-Pump Output. V_DD is regulated to 5.5V. Bypass V_DD to GND with a 4.7µF
capacitor. V_DD is connected to IN when ONBIAS is pulled low.
—
EP
Exposed Paddle. Connect directly to a ground plane, GND, and PGND directly under the IC.
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