User Manual

MAX1578/MAX1579
Complete Bias and White LED Power Supplies
for Small TFT Displays
4 _______________________________________________________________________________________
Note 1: All devices are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2: V
D1
is the forward-voltage drop of diode D1 in Figure 3.
Note 3: Time from CTRL going below the Dual-Mode threshold to IC shutdown.
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V
IN
= 3V, CTRL = ONBIAS = IN, T
A
= -40°C to +85°C, typical values are at T
A
= +25°C, unless otherwise noted. Note 1)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
N-CHANNEL SWITCH
LX On-Resistance I
LX
= 190mA
0.82
1.5 Ω
T
A
= +25°C
0.01
5
LX Leakage Current V
LX
= 28V, CTRL = GND
T
A
= +85°C 1
µA
LX Current Limit Duty cycle = 90%
500 700 900
mA
Typical Operating Characteristics
(Circuit of Figure 3, V
IN
= 3.6V, I
LED
= 20mA, 4 LEDs, CTRL = IN, T
A
= +25°C, unless otherwise noted.)
50
55
60
65
70
75
80
85
90
0 5 10 15 20 25
LED EFFICIENCY vs. I
LED
MAX1578toc01
LED CURRENT (mA)
EFFICIENCY (%)
2 LEDs
4 LEDs
6 LEDs
8 LEDs
50
55
60
65
70
75
80
85
90
2.5 3.0 3.5 4.0 4.5 5.0 5.5
LED EFFICIENCY vs. V
IN
MAX1578toc02
INPUT VOLTAGE (V)
EFFICIENCY (%)
I
LED
= 2mA
I
LED
= 10mA
I
LED
= 20mA
0
10
5
20
15
25
30
-40 85
LED CURRENT vs. TEMPERATURE
MAX1578toc03
TEMPERATURE (°C)
I
LED
(mA)
10-15 35 60
MAX1579
R
CS
= 13
Ω
MAX1578
R
CS
= 22
Ω
0
5
15
10
20
25
01.00.5 1.5 2.0 2.5
LED CURRENT vs. V
CTRL
MAX1578toc04
CTRL VOLTAGE (V)
I
LED
(mA)