Rainbow Electronics MAX1779 - Manual (Page 8)

MAX1779
Low-Power Triple-Output TFT LCD DC-DC
Converter
8 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 RDY Active-Low Open-Drain Output. Indicates all outputs are ready. The on-resistance is 125 Ω (typ).
2 FB
Main Boost Regulator Feedback Input. Regulates to 1.25V nominal. Connect feedback resistive
divider to analog ground (GND).
3 INTG
Main Boost Integrator Output. If used, connect 2200pF to analog ground (GND). To disable
integrator, connect to REF.
4 IN
Supply Input. +2.7V to +5.5V input range. Bypass with a 0.1 µF capacitor between IN and GND, as
close to the pins as possible.
5 GND Analog Ground. Connect to power ground (PGND) underneath the IC.
6 REF
Internal Reference Bypass Terminal. Connect a 0.22 µF capacitor from this terminal to analog ground
(GND). External load capability to 50 µA.
7 FBP
Positive Charge-Pump Regulator Feedback Input. Regulates to 1.25V nominal. Connect feedback
resistive divider to analog ground (GND).
8 FBN Negative Charge-Pump Regulator Feedback Input. Regulates to 0V nominal.
9 SHDN Active-Low Logic-Level Shutdown Input. Connect SHDN to IN for normal operation.
Typical Operating Characteristics (continued)
(Circuit of Figure 5, V IN = +3.3V, T A = +25°C, unless otherwise noted.)
4ms/div
POWER-UP SEQUENCING
MAX1779-23
A. V SHDN = 0 to 2V, 2V/div
B. V MAIN = 5V, R MAIN = 50 Ω, 2.5V/div
C. V NEG = -8V, R NEG = 8k Ω, 10V/div
D. V POS = +12V, R POS = 12k Ω, 10V/div
2V
10V
A
B
0
-10V
0
5V
C
0
D
200 µs/div
STARTUP WAVEFORM
(L = 33 µH)
MAX1779-22
A. V SHDN = 0 to 2V, 2V/div
B. V MAIN = 5V, 1V/div
C. I L , 500mA/div
R MAIN = 50 Ω
2V
0
A
B
3V
500mA
0
5V
C