add8754dacpz-reel7 Analog Devices, Inc., add8754dacpz-reel7 Datasheet - Page 13

• Manufacturer Part Number: add8754dacpz-reel7
• Description: Lcd Panel Power, Vcom, And Gate Modulation
• Manufacturer: Analog Devices, Inc.

Inductor Selection
The inductor is an integral part of the step-up converter. It
stores energy during the switch-on time and transfers that
energy to the output through the output diode during the
switch-off time. Use inductance in the range of 1 μH to 22 μH.
In general, lower inductance values have higher saturation
current and lower series resistance for a given physical size.
However, lower inductance results in higher peak current,
which can lead to reduced efficiency and greater input and/or
output ripple and noise. Peak-to-peak inductor ripple current at
close to 30% of the maximum dc input current typically yields
an optimal compromise.
For determining the inductor ripple current, the input (V
output (V
the following equation:
Using the duty cycle and switching frequency, f
the on time by using the following equation:
Table 9. Inductor Manufacturers
Vendor
Sumida
Coilcraft
Toko
www.sumida.com
www.coilcraft.com
www.tokoam.com
D =
t =
ON
OUT
V
OUT
f
D
SW
) voltages determine the switch duty cycle (D) by
V
OUT
−
V
IN
Part
CMD4D11-2R2MC
CMD4D11-4R7MC
CDRH4D28-100
CDRH5D18-220
CR43-4R7
CR43-100
DS1608-472
DS1608-103
D52LC-4R7M
D52LC-100M
SW
, determine
L (μH)
2.2
4.7
10
22
4.7
10
4.7
10
4.7
10
IN
) and
Rev. 0 | Page 13 of 28
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The inductor ripple current ( Δ I
Solving for the inductance value, L ,
Make sure that the peak inductor current (the maximum input
current plus half of the inductor ripple current) is less than the
rated saturation current of the inductor. In addition, ensure that
the maximum rated rms current of the inductor is greater than
the maximum dc input current to the regulator.
For duty cycles greater than 50% that occur with input voltages
greater than half the output voltage, slope compensation is
required to maintain stability of the current-mode regulator.
For stable current-mode operation, ensure that the selected
inductance is equal to or greater than L
Max DC Current
0.95
0.75
1.00
0.80
1.15
1.04
1.40
1.00
1.14
0.76
Δ I =
L =
L
L
>
V
L
MIN
IN
V
Δ
IN
×
I
L
=
t
×
L
ON
V
1
t
ON
8 .
OUT
A
×
−
V
f
Max DCR (mΩ)
116
216
128
290
109
182
60
75
87
150
SW
IN
L
) in steady state is
MIN
:
1.2
1.2
3.0
2.0
3.5
3.5
2.9
2.9
2.0
2.0
Height (mm)
ADD8754
(5)
(6)
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