Rainbow Electronics MAX1885 - Manual (Page 11)

MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
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RIPPLE VOLTAGE WAVEFORMS
MAX1778 toc16
8V
-5V
20V
1 µs/div
A. V
MAIN
= 8V, I
MAIN
= 200mA, 10mV/div
B. V NEG = -5V, I NEG = 10mA, 20mV/div
C. V POS = 20V, I POS = 5mA, 20mV/div
C
B
A
STEP-UP CONVERTER
SOFT-START (LIGHT LOAD)
MAX1778 toc17
0
6V
0.5A
1ms/div
A. V SHDN = O TO 2V, 2V/div
B. V MAIN = 8V, 2V/div
C. INDUCTOR CURRENT, 500mA/div
R
LOAD = 400 Ω
C
B
A
2V
8V
4V
0
STEP-UP CONVERTER
SOFT-START (HEAVY LOAD)
MAX1778 toc18
0
6V
1.0A
1ms/div
A. V SHDN = O TO 2V, 2V/div
B. V
MAIN
= 8V, 2V/div
C. INDUCTOR CURRENT, 500mA/div
R
LOAD = 20 Ω
C
B
A
2V
8V
4V
0.5A
0
POWER-UP SEQUENCE
MAX1778 toc19
0
0
10V
2ms/div
A. V SHDN = O TO 2V, 2V/div
B. RDY, 5V/div
C. POSITIVE CHARGE PUMP = V
POS = 20V, R LOAD = 4k Ω, 10V/div
D. STEP-UP CONVERTER: V MAIN = 8V, R LOAD = 40 Ω, 10V/div
E. NEGATIVE CHARGE PUMP: V NEG = -5V, R LOAD = 500 Ω, 10V/div
E
B
A
2V
5V
20V
0
-10V
C
D
POWER-UP SEQUENCE
(CIRCUIT OF FIG.10)
MAX1778 toc20
0
10V
0
1ms/div
A. RDY, 2V/div
B. POSITIVE CHARGE PUMP, V
POS(SYS) = 20V, 10V/div
C. STEP-UP CONVERTER: V MAIN(SYS) = 8V, 10V/div
D. NEGATIVE CHARGE PUMP, V NEG = -5V, -5V/div
B
A 2V
20V
0
-5V
C
D
4V
MAX1778 toc21
C
B
A
10V
5V
4V
5V
2V
0
0
0
100 µs/div
POWER-UP INTO SHORT-CIRCUIT
(CIRCUIT OF FIG. 10)
A. RDY, 2V/div
B. GATE OF N-CH MOSFET, 5V/div
C. STEP-UP CONVERTER, V
MAIN(START) = 8V, 5V/div
V MAIN(SYS) = GND
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.)