MP1531 – LOW POWER, TRIPLE OUTPUT STEP-UP PLUS CHARGE PUMP FOR TFT BIAS
Selecting the Inductor
The inductor is required to force the higher
output voltage while being driven by the input
voltage. A larger value inductor results in less
ripple current that results in lower peak inductor
current. However, the larger value inductor has
a larger physical size, higher series resistance,
lower saturation current for a given package
size.
Choose an inductor that does not saturate at
heavy load transients and start-up conditions. A
good rule for determining the inductance is to
allow the peak-to-peak ripple current to be
approximately 30-50% of the maximum input
current. Make sure that the peak inductor
current is below the device current limit to
prevent loss of regulation. Calculate the
required inductance value by the equation:
V
IN
(
V
MAIN
−
V
IN
)
V
MAIN
×
f
SW
× ∆
I
L1
=
Where V
IN
is the input voltage, f
SW
is the
switching frequency, and
∆I
is the peak-to-peak
inductor ripple current.
Selecting the Input Capacitor
An input capacitor is required to supply the AC
ripple current to the inductor, while limiting noise
at the input source. A low ESR capacitor is
required to keep the noise at the IC to a minimum.
Since it absorbs the input switching current it
requires an adequate ripple current rating. Use a
capacitor with RMS current rating greater than the
inductor ripple current (see
Selecting The Inductor
to determine the inductor ripple current). The
input capacitor in Figure 3 is necessary in most
lab setups, but can be reduced in typical
application circuits if the source impedance is
lower.
V
IN
2.7V to 4.2V
C4
10nF
CT
EN
RDY
COMP
C3
10nF
IN2
D7
BAS40-04-7
D6
BAS40-04-7
D5
BAS40-04-7
GL
FB2
C9
56pF
REF
GND
FB3
PGND
C7
56pF
IN
SW
FB1
D1
B0530W
OFF ON
RDY
SW
V
MAIN
5V
D2
BAS40-04-7
MP1531
IN3
D4
BAS40-04-7
GH
D3
BAS40-04-7
V
GL
-10V
V
GH
15V
Figure 3—Triple Output Boost Application Circuit
MP1531 Rev. 1.2
5/22/2006
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