Rainbow Electronics MAX1885 - Manual (Page 10)

MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
10 ______________________________________________________________________________________
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.)
30
50
40
70
60
90
80
100
NEGATIVE CHARGE-PUMP EFFICIENCY
vs. LOAD CURRENT
MAX1778 toc10
I NEG (mA)
EFFICIENCY (%)
0 10 20 30 40
V SUPN = 7V
V SUPN = 8V
V SUPN = 6V
V NEG = -5V
-14
-10
-12
-6
-8
-4
-2
2 6 8 4 10 12 14
MAXIMUM NEGATIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1778 toc11
V SUPN (V)
V
NEG
(V)
I NEG = 10mA
I NEG = 1mA
1.23
1.24
1.25
1.26
1.27
0 20 40 60 80 100
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
MAX1778 toc12
I REF ( µA)
V
REF
(V)
STEP-UP CONVERTER LOAD-TRANSIENT
RESPONSE
MAX1778 toc13
200mA
0
8.1V
8.0V
7.9V
1A
0
40 µs/div
A. I MAIN = 20mA to 200mA, 200mA/div
B. V MAIN = 8V, 100mV/div
C. INDUCTOR CURRENT, 1A/div
C
INTG = 1000pF
C
B
A
STEP-UP CONVERTER LOAD-TRANSIENT
RESPONSE WITHOUT INTEGRATOR
MAX1778 toc14
200mA
0
8.1V
8.0V
7.9V
1A
0
40 µs/div
A. I MAIN = 20mA to 200mA, 200mA/div
B. V MAIN = 8V, 100mV/div
C. INDUCTOR CURRENT, 1A/div
INTG = REF
C
B
A
STEP-UP CONVERTER LOAD-TRANSIENT
RESPONSE (1 µs PULSES)
MAX1778 toc15
0.5A
0
8.0V
7.9V
1A
0.5A
0
4 µs/div
A. I MAIN = 0 to 500mA, 500mA/div
B. V MAIN = 8V, 100mV/div
C. INDUCTOR CURRENT, 500mA/div
C
B
A