Rainbow Electronics MAX749 - Manual (Page 9)

Figure 9b. Maximum Output Current vs. Input Voltage,
V
OUT = -12V
Figure 9c. Maximum Output Current vs. Input Voltage,
V
OUT = -15V
Figure 9d. Maximum Output Current vs. Input Voltage,
V
OUT = -24V
Figure 9e. Maximum Output Current vs. Input Voltage,
V
OUT = -48V
Choosing an Inductor
Practical inductor values range from 22µH to 100µH,
and 47µH is normally a good choice. Inductors with a
ferrite core or equivalent are recommended. The induc-
tor’s saturation current rating – the current at which the
core begins to saturate and the inductance falls to 80%
or 90% of its nominal value – should ideally equal the
current limit (see
Current-Sense Resistor section).
However, because the current is limited by the
MAX749, the inductor can safely be driven into satura-
tion with only a slight impact on efficiency.
For highest efficiency, use a coil with low resistance,
preferably under 300m
Ω . To minimize radiated noise,
use a toroid, pot-core, or shielded inductor.
MAX749
Digitally Adjustable LCD Bias Supply
_______________________________________________________________________________________ 9
Figure 9a. Maximum Output Current vs. Input Voltage,
V
OUT = -5V
0
MAX749-Fig 13
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
R
SENSE
(
Ω
)
5
10
15
20
25
3 2 4 5 6
1.0
0.5
0.3
0.25
0.2
V OUT = -48V
L = 47 µ H
80
0
2 6
20
60
MAX-749-Fig10
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
4
40
100
120
140
3 5
V OUT = -12V
L = 47 µ H
R
SENSE
(
Ω
)
0.2
0.25
0.3
0.5
1.0
60
0
MAX749-Fig 11
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
6
20
2 4
40
80
100
3 5
R
SENSE
(
Ω
)
V OUT = -15V
L = 47 µ H
0.2
0.25
0.3
0.5
1.0
60
0
10
50
MAX749-Fig 12
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
6
30
20
2 4
40
3 5
R
SENSE
(
Ω
)
1.0
0.5
0.3
0.25
0.2
V OUT = -24V
L = 47 µ H
0
MAX749-Fig 9
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
R
SENSE
(
Ω
)
50
100
150
200
250
3 2 4 5 6
1.0
0.5
0.3
0.25
0.2
V OUT = -5V
L = 47 µ H