Rainbow Electronics MAX1885 - Manual (Page 13)

MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
______________________________________________________________________________________ 13
0
1 1000 100 10
100
40
20
80
60
MAX1778 toc27
FREQUENCY (kHz)
PSRR (dB)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
C LDOOUT = 4.7 µF
I LDOOUT = 40mA
0 40
REGION OF STABLE C LDOOUT ESR
vs. LOAD CURRENT
MAX1778 toc28
I
LDOOUT
(mA)
C
LDOOUT
ESR (
Ω
)
10 20 30
100
0.01
0.1
10
1
C LDOOUT = 1 µF
STABLE REGION
MAX1778 toc29
B
A
4.96V
4OmA
0
5.00V
100 µs/div
LOAD-TRANSIENT RESPONSE
(INTERNAL LINEAR REGULATOR)
A. I
LDO
= 100 µA TO 40mA, 40mA/div
B. V LDO = 5V, 20mV/div
V SUPL = V LDO + 500mV
MAX1778 toc30
B
A
4.94V
4OmA
0
5.00V
100 µs/div
LOAD-TRANSIENT RESPONSE NEAR
DROPOUT (INTERNAL LINEAR REGULATOR)
A. I LDO = 100 µA TO 40mA, 40mA/div
B. V LDO = 5V, 20mV/div
V IN = V LDO + 100mV
MAX1778 toc31
C
B
A
0.5A
0
5.0V
8.0V
1.0A
10 µs/div
INTERNAL LINEAR-REGULATOR
RIPPLE REJECTION
A. V LDOOUT = 5V, I LDOOUT = 40mA, 10mV/div
B. V MAIN = V SUPL = 8V, 200mV/div
C. I MAIN = 0 TO 750mA, 500mA/div
MAX1778 toc32
C
B
A
4V
2V
2V
0
2V
4V
0
400 µs/div
INTERNAL LINEAR-REGULATOR
STARTUP
A. V S HDN = 0 TO 2V, 2V/div
B. V LDOOUT = 5V, R LDOOUT = 125 Ω, 2V/div
C. V MAIN = 8V, R MAIN = 40 Ω, 2V/div
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.)