MAX686 Datasheet, PDF (7/16 Pages) Maxim Integrated Products – DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch

DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
_____________________________Typical Operating Characteristics (continued)
(Circuits of Figures 1 and 2, V_CC = V_DD = V_IN = +5V, L1 = 22µH, SHDN = V_CC, C_REF = 0.1µF, TA = +25°C, unless otherwise noted.)
POWER-UP RESPONSE
(NEGATIVE CONFIGURATION)
MAX686 TOC14A
POWER-DOWN RESPONSE
(NEGATIVE CONFIGURATION)
MAX686 TOC14B
SHDN
5V/div
SHDN
5V/div
I_SET = V_CC
R_L = 4.7kΩ
0V
0V
V_OUT
5V/div
I_SET = V_CC
R_L = 4.7kΩ
500µs
-16.8V
V_OUT
5V/div
-16.8V
20ms/div
Pin Description
PIN
NAME
FUNCTION
1
PGND Power Ground. Connect to GND.
2
UP
Increment Output Voltage Input. Increments the DAC on each rising edge such that |V_OUT| increases.
3
DN
Decrement Output Voltage Input. Decrements the DAC on each rising edge such that |V_OUT| decreases.
Polarity Input. Changes polarity and threshold of FB to allow regulation of either positive or negative output
4
POL
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 = V_CC for negative
output voltage.
5
V_DD
Gate-Drive Supply for Internal MOSFET. Connect to V_CC.
6
ISET
Set LX Current Limit. Sets the peak current limit for the internal switch. Connect to V_CC for 500mA current
limit. Connect to GND for 250mA current limit.
7
SHDN
Shutdown Input. A logic low on SHDN places the MAX686 in shutdown mode. Connect to V_CC for normal
operation.
8
DACOUT DAC Output Voltage
9
REF
Reference Output. Bypass with a 0.1µF ceramic capacitor to GND.
10
FB
Feedback Input. Connect to an external voltage divider to set the MAX686 output voltage. See the section
Setting the Output Voltage with the DAC.
11
POK
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 V_IN or V_OUT.
12
V_CC
IC Power-Supply Input
13
GND
Ground
14
LCDON
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.
15
N.C.
No Connection. Not internally connected.
16
LX
Drain of Internal 28V, 500mA N-Channel Switch
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