Rainbow Electronics MAX1885 - Manual (Page 16)

MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
16 ______________________________________________________________________________________
MAX1778 toc48
B
A
4.00V
3.50V
4.50V
4.00V
3.50V
4.50V
10 µs/div
VCOM BUFFER
LARGE-SIGNAL RESPONSE
A. V BUF + = 3.50V TO 4.50V, 0.5V/div
B. BUFOUT = BUF-, 0.5V/div
C
BUF = 1 µF, V
SUPB = 8V
MAX1778 toc49
C
B
A
3.8V
8.0V
200mA
4.2V
0
-200mA
4.0V
4 µs/div
VCOM BUFFER
LOAD-TRANSIENT RESPONSE
A. I BUFOUT = 200mA PULSES, 200mA/div
B. BUFOUT = BUF-, 200mV/div
C. V
MAIN = 8V, 50mV/div
V SUPB = V MAIN , BUF+ = GND, C BUF = 1 µF
MAX1778 toc50
C
B
A
3.5V
8.0V
500mA
4.5V
0
-500mA
4.0V
4 µs/div
VCOM BUFFER
LOAD-TRANSIENT RESPONSE
A. I BUFOUT = 400mA PULSES, 500mA/div
B. BUFOUT = BUF-, 0.5V/div
C. V
MAIN = 8V, 100mV/div
V SUPB = V MAIN , BUF+ = GND, C BUF = 1 µF
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V IN = +3.3V, SHDN = IN, V MAIN = V SUPP = V SUPN = V SUPB = V SUPL = 8V, BUF- = BUFOUT,
BUF+ = FLTSET = TGND = PGND = GND, T A = +25°C.)
MAX1778 toc51
C
B
A
8.1V
7.8V
2V
4V
2V
0
4V
0
100 µs/div
VCOM BUFFER STARTUP
A. RDY, 2V/div
B. BUFOUT = BUF-, C
BUF = 1 µF, 2V/div
C. V SUPB = V MAIN = 8V, I MAIN = 20mA, 200mV/div
BUF+ = GND
MAX1778 toc51
C
B
A
8.1V
7.8V
2V
4V
2V
0
4V
0
100 µs/div
VCOM BUFFER STARTUP
A. RDY, 2V/div
B. BUFOUT = BUF-, C
BUF = 1 µF, 2V/div
C. V SUPB = V MAIN = 8V, I MAIN = 20mA, 200mV/div
BUF+ = GND