MAX1514 Maxim Integrated Products, MAX1514 Datasheet - Page 18

• Manufacturer Part Number: MAX1514
• Description: (MAX1513 / MAX1514) TFT-LCD Power-Supply Controllers
• Manufacturer: Maxim Integrated Products

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taken from an appropriate curve in the Typical
Operating Characteristics, and an estimate of LIR
based on the above paragraphs:
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input cur-
rent at the minimum input voltage (V
following equation:
The expected efficiency at that operating point (η
can be taken from an appropriate curve in the Typical
Operating Characteristics.
Calculate the ripple current at that operating point and
the peak current required for the inductor:
The inductor’s saturation current rating and the
MAX1513/MAX1514s’ current limit (I
I
exceed I
Considering the typical operating circuit, the maximum
load current (I
and 30mA for REG G to provide V
stage negative charge pump provides 30mA to REG N
for V
provides 20mA to REG P for V
effective maximum output current (I
with a 15V output and a typical 5V input voltage. The
switching frequency is set to 1.5MHz. Choosing an
LIR of 0.6 and estimating efficiency of 85% at this
operating point:
Using the circuit’s minimum input voltage (4.5V) and
estimating efficiency of 80% at that operating point:
TFT-LCD Power-Supply Controllers
18
PEAK
L
______________________________________________________________________________________
GOFF
, and the inductor’s DC current rating should
=
L
I
RIPPLE
⎛
⎜
⎝
I
IN(DC, MAX)
PEAK
=
I
I
IN DC MAX
15
IN DC MAX
5
, and the one-stage positive charge pump
(
(
⎛
⎜
⎝
V
V
V
⎞
⎟
⎠
MAIN
V
,
,
2
MAIN(MAX)
IN
=
=
⎛
⎜
⎝
0 5
I
V
IN DC MAX
.
⎞
⎟
⎠
IN MIN
)
.
)
(
15
2
A
(
⎛
⎜
⎝
=
=
V
I
×
MAIN EFF
L
,
I
0 5
-
MAIN EFF
) is 400mA for I
1 5
4 5
)
V
×
.
.
.
V
MAIN
5
×
IN MIN
(
A
MHz
)
V
V
V
MAIN
(
(
+
(
V
×
×
MAIN
)
I
RIPPLE
-
15
⎞
⎟
⎠
GON
0 8
×
)
)
⎛
⎜
⎝
.
V
× η
MAIN(EFF)
2
V
×
0 85
×
IN
LIM
0 6
f
OSC
.
GAMMA
.
-
IN(MIN)
. Altogether, the
f
V
OSC
≈
MIN
) should exceed
MAIN
V
⎞
⎟ ≈
⎠
IN MIN
2 1
⎞
⎟
⎠
MAIN
.
⎛
⎜
⎝
(
η
A
) using the
LIR
. The one-
) is 500mA
TYP
2 2
.
)
)
directly
µ
⎞
⎟
⎠
DataSheet4U.com
H
MIN
)
The ripple current and the peak current are:
The inductor DCR should be low enough for reasonable
efficiency. As a rule of thumb, do not allow the voltage
drop across the inductor DCR to exceed a few percent
of the input voltage at I
Many notebook panel designs have height constraints
on the components. If a thin inductor with the required
current rating is not available, use two thin inductors in
series or parallel.
After selecting the inductor, use the following steps to
design the current-sense network for lossless current
sensing.
1) Calculate the RC time constant of the sense network
using the typical inductance and typical DCR:
2) Determine the component values of the sense net-
work. Select C
3) Calculate the worst-case high sense voltage over
temperature using the maximum DCR value (R
found in the inductor technical specifications:
where I
the Inductor Selection section, TC is the temperature
coefficient of copper (0.5%/°C) and ∆T is the difference
between the specified temperature for R
maximum expected inductor temperature.
4) Compare the calculated sense voltage with the mini-
mum value of the current-limit threshold in the Electrical
Characteristics (100mV). If the sense voltage is between
80mV and 100mV, use the current-sense configuration
in Figure 8 with the calculated C
V
SENSE
I
RIPPLE
PEAK
I
PEAK
is the peak inductor current calculated in
=
S
=
=
, and then calculate R
I
PEAK
2 1
2 2
.
.
4 5
A
Current-Sense Network Selection
τ
.
µ
R
H
+
V
S
×
PEAK
=
×
1 0
×
R
=
R
.
L MAX
2
15
L TYP
(
(
.
15
A
(
C
L
V
τ
S
V
≈
S
×
)
)
-
and R
2 6
1 5
×
4 5
.
.
.
(
A
MHz
1
S
V
+
)
using:
S
L(MAX)
above.
TC
≈
×
1 0
.
and the
∆
L(MAX)
A
T
)
)
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