Manual

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 10203040
V
SUPN
= 7V
V
SUPN
= 8V
V
SUPN
= 6V
V
NEG
= -5V
-14
-10
-12
-6
-8
-4
-2
2684 101214
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 20406080100
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
MAX1778 toc12
I
REF
(
µ
A)
V
REF
(V)
STEP-UP CONVERTER LOAD-TRANSIENT
RESPONSE
MAX1778 toc13
200mA
0
8.1V
8.0V
7.9V
1A
0
40
µ
s/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
µ
s/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
µ
s PULSES)
MAX1778 toc15
0.5A
0
8.0V
7.9V
1A
0.5A
0
4
µ
s/div
A. I
MAIN
= 0 to 500mA, 500mA/div
B. V
MAIN
= 8V, 100mV/div
C. INDUCTOR CURRENT, 500mA/div
C
B
A