Typical operating characteristics (continued) – Rainbow Electronics MAX1579 User Manual
Page 5
Typical Operating Characteristics (continued)
(Circuit of Figure 3, V
IN
= 3.6V, I
LED
= 20mA, 4 LEDs, CTRL = IN, T
A
= +25
°C, unless otherwise noted.)
MAX1578/MAX1579
Complete Bias and White LED Power Supplies
for Small TFT Displays
_______________________________________________________________________________________
5
PWM-DIMMING WAVEFORMS
MAX1578toc08
V
CTRL
I
IN
V
OUT
AC-COUPLED
V
IN
AC-COUPLED
2V/div
50mV/div
20mA/div
20mV/div
40
µs/div
0
400
200
800
600
1200
1000
1400
0
2
3
1
4
5
LCD BIAS SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1578toc09
INPUT VOLTAGE (V)
I
IN
(µ
A)
V
CTRL
= 0V
LCD BIAS STARTUP SEQUENCE
MAX1578toc10
V
ONBIAS
V
POS
V
NEG
V
MAIN
5V/div
5V/div
10V/div
5V/div
10ms/div
BOOST STARTUP AND
SHUTDOWN WAVEFORMS
MAX1578toc07
V
CTRL
I
IN
V
OUT
V
IN
AC-COUPLED
2V/div
5V/div
0V
100mA/div
20mV/div
4ms/div
0
5
10
15
20
25
0
40 50
20 30
10
60 70 80 90 100
LED CURRENT vs.
DIRECT-PWM DUTY CYCLE
MAX1578toc05
PWM DUTY CYCLE (%)
I
LED
(mA)
f
PWM
= 200Hz TO 200kHz
BOOST-SWITCHING WAVEFORMS
MAX1578toc06
V
IN
AC-COUPLED
V
LX
V
OUT
AC-COUPLED
20mV/div
10V/div
200mV/div
400ns/div