
MAX1748
Triple-Output TFT LCD DC-DC Converter
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 5, V
IN
= 3.3V, T
A
= +25°C, unless otherwise noted.)
8
10
18
20
12
16
14
22
24
58796101112
MAXIMUM POSITIVE CHARGE-PUMP OUTPUT
VOLTAGE vs. SUPPLY VOLTAGE
MAX1748toc10
V
SUPP
(V)
V
POS
(V)
I
POS
= 10mA
V
POS
= 22V
I
POS
= 1mA
I
POS
= 20mA
0.80
0.85
0.90
1.05
1.00
0.95
1.10
1.15
1.20
2.5 3.53.0 4.0 4.5 5.0 5.5
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX1748toc11
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (MHz)
MEASURED FROM THE
FALLING EDGE OF LX
V
MAIN
= 10V
I
MAIN
= 100mA
1.244
1.246
1.250
1.248
1.252
1.254
0201510 3025535404550
REFERENCE VOLTAGE
vs. REFERENCE LOAD CURRENT
MAX1748toc12
I
REF
(µA)
V
REF
(V)
V
IN
= 3.3V
V
MAIN
10mV/div
V
NEG
10mV/div
V
POS
10mV/div
RIPPLE WAVEFORMS
MAX1748toc13
1µs/div
V
MAIN
= 10V, I
MAIN
= 200mA,
V
NEG
= -5V, I
NEG
= 10mA,
V
POS
= 15V, I
POS
= 10mA
I
MAIN
200mA/div
I
LX
500mA/div
V
MAIN
200mV/div
LOAD-TRANSIENT RESPONSE
MAX1748 toc14
100µs/div
V
IN
= 3.3V, V
MAIN
= 10V,
R
MAIN
= 500Ω TO 50Ω (20mA TO 200mA)
I
MAIN
200mA/div
I
LX
500mA/div
V
MAIN
200mV/div
LOAD-TRANSIENT RESPONSE
WITHOUT INTEGRATOR
MAX1748toc15
100µs/div
V
IN
= 3.3V, V
MAIN
= 10V, INTG = REF,
R
MAIN
= 500Ω TO 50Ω (20mA TO 200mA)
-11
-9
-10
-7
-8
-4
-5
-6
-3
5867 9101112
MAXIMUM NEGATIVE CHARGE-PUMP
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX1748toc07
V
SUPN
(V)
V
NEG
(V)
I
NEG
= 20mA
I
NEG
= 1mA
I
NEG
= 10mA
V
NEG
= -10mA
14.4
14.5
14.6
14.9
15.0
14.7
14.8
15.2
15.1
15.3
086102 4 12 14 16 18 20
POSITIVE CHARGE-PUMP OUTPUT
VOLTAGE vs. LOAD CURRENT
MAX1748toc08
I
POS
(mA)
V
POS
(V)
V
SUPN
= 12V
V
SUPN
= 8V
V
SUPN
= 10V
40
50
80
60
70
90
100
086102 4 12 14 16 18 20
POSITIVE CHARGE-PUMP EFFICIENCY
vs. LOAD CURRENT
MAX1748toc09
I
POS
(mA)
EFFICIENCY (%)
V
SUPP
= 12V
V
SUPP
= 8V
V
SUPP
= 10V
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