Datasheet
MAX1513/MAX1514
TFT-LCD Power-Supply Controllers
______________________________________________________________________________________ 19
5) If V
SENSE
is greater than 100mV, the current-feed-
back signal is too high and can trip the current limit
before the full load current is delivered. Use the cur-
rent-sense configuration in Figure 9 to attenuate the
sense signal. Define the scale factor (SF) as:
Calculate R
S1
and R
S2
:
6) If V
SENSE
is less than 80mV, the current-feedback
signal is low relative to the current-limit threshold. Use
the Figure 8 configuration, or, if good current-limit
accuracy is desired, use the optional current-sense
configuration in Figure 10 to increase the amplitude of
the sense signal. Calculate R
S3
and R
S4
:
If the 2.2µH inductor used in the typical operating cir-
cuit (Figures 1 and 2) had a typical DCR of 24mΩ and a
maximum DCR of 30mΩ, the RC time constant of the
sense network would be:
Select C
S
= 0.1µF and calculate R
S
:
Assuming ∆T is 40°C and TC is 0.5%, the worst-case
high sense voltage over temperature is:
Because V
SENSE
would be between 80mV and 100mV,
the circuit in Figure 8 should be used. The closest 1%
standard value for R
S
is 909Ω.
If the 2.2µH inductor used in the typical operating cir-
cuit (Figures 1 and 2) has a typical DCR of 45mΩ and a
maximum DCR of 56mΩ, the RC time constant of the
sense network is:
Select C
S
= 0.1µF and calculate R
S
:
Assuming ∆T is 40°C and TC is 0.5%, the worst-case
high sense voltage over temperature is:
R
s
F
S
.
.
==
48 9
01
489
µ
µ
Ω
τ
µ
µ
.
.==
22
45
48 9
H
m
s
Ω
VAm CmV
SENSE
. . .=× +×°
()
=2 6 30 1 0 005 40 93 6Ω
R
s
F
S
.
.
==
91 7
01
917
µ
µ
Ω
τ
µ
µ
.
.==
22
24
91 7
H
m
s
Ω
R
VV
V V mV V
R
RRR
S
MAIN IN MIN
MAIN IN MIN SENSE
S
SSS
3
43
100
()
()
=
+
×
=
-
--
-
R
R
SF
R
RSF
SF
S
S
S
S
1
2
1
1
=
=
×
-
SF
mV
V
SENSE
=
100
MAX1513
MAX1514
L
R
S
C
S
V
IN
V
MAIN
C
S+
C
S-
GATE
GND
FB
Figure 8. Lossless Current Sensing with 80mV < V
SENSE
< 100mV
MAX1513
MAX1514
L
R
S1
C
S
V
IN
V
MAIN
C
S+
C
S-
GATE
GND
FB
R
S2
Figure 9. Lossless Current Sensing with V
SENSE
> 100mV