Typical operating characteristics (continued), Pin description – Rainbow Electronics MAX686 User Manual
Page 7
MAX686
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
_______________________________________________________________________________________
7
_____________________________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.)
V
OUT
5V/div
-16.8V
0V
POWER-UP RESPONSE
(NEGATIVE CONFIGURATION)
MAX686 TOC14A
500
µ
s
SHDN
5V/div
I
SET
= V
CC
R
L
= 4.7k
Ω
V
OUT
5V/div
-16.8V
0V
POWER-DOWN RESPONSE
(NEGATIVE CONFIGURATION)
MAX686 TOC14B
20ms/div
SHDN
5V/div
I
SET
= V
CC
R
L
= 4.7k
Ω
Reference Output. Bypass with a 0.1µF ceramic capacitor to GND.
REF
9
Feedback Input. Connect to an external voltage divider to set the MAX686 output voltage. See the section
Setting the Output Voltage with the DAC
.
FB
10
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
.
POK
11
IC Power-Supply Input
V
CC
12
Ground
GND
13
Gate-Drive Supply for Internal MOSFET. Connect to V
CC
.
V
DD
5
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.
ISET
6
Shutdown Input. A logic low on SHDN places the MAX686 in shutdown mode. Connect to V
CC
for normal
operation.
SHDN
7
DAC Output Voltage
DACOUT
8
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 = V
CC
for negative
output voltage.
POL
4
Decrement Output Voltage Input. Decrements the DAC on each rising edge such that
|
V
OUT
|
decreases.
DN
3
PIN
Increment Output Voltage Input. Increments the DAC on each rising edge such that
|
V
OUT
|
increases.
UP
2
Power Ground. Connect to GND.
PGND
1
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
14
No Connection. Not internally connected.
N.C.
15
Drain of Internal 28V, 500mA N-Channel Switch
LX
16
Pin Description