Datasheet

MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC/DC
Converters with Buffer
11
Maxim Integrated
RIPPLE VOLTAGE WAVEFORMS
MAX1778 toc16
8V
-5V
20V
1µs/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
= 400Ω
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
= 20Ω
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
= 4kΩ, 10V/div
D. STEP-UP CONVERTER: V
MAIN
= 8V, R
LOAD
= 40Ω, 10V/div
E. NEGATIVE CHARGE PUMP: V
NEG
= -5V, R
LOAD
= 500Ω, 10V/div
E
B
A
2V
5V
20V
0
-10V
C
D
POWER-UP SEQUENCE
(CIRCUIT OF FIGURE 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
100µs/div
POWER-UP INTO SHORT-CIRCUIT
(CIRCUIT OF FIGURE 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.)