MAX686EEE datasheet(7/16 Pages) MAXIM

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DAC-Controlled Boost/Inverter

LCD Bias Supply with Internal Switch

_______________________________________________________________________________________

_____________________________Typical Operating Characteristics (continued)

(Circuits of Figures 1 and 2, VCC = VDD = VIN = +5V, L1 = 22µH, SHDN = VCC, CREF = 0.1µF, TA = +25°C, unless otherwise noted.)

VOUT

5V/div

-16.8V

POWER-UP RESPONSE

(NEGATIVE CONFIGURATION)

MAX686 TOC14A

500

µs

SHDN

5V/div

ISET = VCC

RL = 4.7kΩ

VOUT

5V/div

-16.8V

POWER-DOWN RESPONSE

(NEGATIVE CONFIGURATION)

MAX686 TOC14B

20ms/div

SHDN

5V/div

ISET = VCC

RL = 4.7kΩ

Reference Output. Bypass with a 0.1µF ceramic capacitor to GND.

REF

Feedback Input. Connect to an external voltage divider to set the MAX686 output voltage. See the section

Setting the Output Voltage with the DAC.

Power-OK Sense Input/Power-OK Comparator Input. When the voltage applied to POK is greater than

1.125V, LCDON is low. Connect to a resistive voltage divider monitoring VIN or VOUT.

POK

IC Power-Supply Input

VCC

Ground

GND

Gate-Drive Supply for Internal MOSFET. Connect to VCC.

VDD

Set LX Current Limit. Sets the peak current limit for the internal switch. Connect to VCC for 500mA current

limit. Connect to GND for 250mA current limit.

ISET

Shutdown Input. A logic low on SHDN places the MAX686 in shutdown mode. Connect to VCC for normal

operation.

SHDN

DAC Output Voltage

DACOUT

Polarity Input. Changes polarity and threshold of FB to allow regulation of either positive or negative output

voltages. POL also changes the polarity of the DAC output such that increasing codes always increases the

magnitude of the output voltage. Set POL = GND for positive output voltage, or set POL = VCC for negative

output voltage.

POL

Decrement Output Voltage Input. Decrements the DAC on each rising edge such that

|VOUT| decreases.

Increment Output Voltage Input. Increments the DAC on each rising edge such that

|VOUT| increases.

Power Ground. Connect to GND.

PGND

FUNCTION

NAME

Power-OK Comparator Open-Drain Output. Connect to external switch to turn LCD power on or off. See the

section

Controlling the LCD Using POK and LCDON.

LCDON

No Connection. Not internally connected.

N.C.

Drain of Internal 28V, 500mA N-Channel Switch

Pin Description

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