Datasheet

LTC3816
36
3816f
applicaTions inForMaTion
For this example, a Vishay IHLP-5050CE-01 0.33µH induc-
tor is chosen. According to the inductor data sheet, it has
a maximum DC current rating of 36.5A and a saturation
current of 62A. At room temperature, the typical DCR is
1.3mΩ and the maximum DCR is 1.5mΩ. At 125°C, the
DCR increases to approximately 2.085mΩ. The R
IMAX
resistor value can be calculated.
R I
I
R
I
A
IMAX LIMIT
L
DCR
IMAX MIN
= +






=
∆
2
29 75
2
( )
. •
.
0085
9
6 89
m
µA
k
Ω
= .
Choose 1% resistor R
IMAX
= 6.98k to ensure that the
regulator can supply the maximum load current under
the worst-case conditions.
If this large DCR variation is a problem, replace this induc-
tor with another inductor with a smaller DCR variation or
use an NTC temperature compensation circuit as shown in
Figure
21. Please refer to the Temperature Compensated
Active Voltage Positioning with Inductor DCR section.
Note that Figure 21 uses a resistive divider and requires
different component values for optimal temperature
compensation.
To derive the voltage drop across the inductor DCR (typically
1.3mΩ), place a 0.1µF capacitor across the current sense
input pins, I
SENP
and I
SENN
. The current sense filter resistor
value R
IDCR
can be calculated from the equation:
R
L
R C
µH
m µF
k
IDCR
DCR IDCR
= = =
•
.
. • .
.
0 33
1 3 0 1
2 538
Ω
Select R
IDCR
= 2.55k.
For the AVP section (refer to Figure 10), first select a 10k
NTC thermistor. In this example, the Murata NCP18XH103
is chosen. Next, select:
R
PAR
= R
NTC
at 25°C = 10k
The R
SER
resistor value can be obtained from the follow-
ing equation:
R R R
SER PAR PAR
≈
( )
( )
10
3
|| – ||R at 0°C R at 75°
NTC NTC
CC
( )
( )




°
( )
( )
– ||R R at C
PAR NTC
25
From the NTC data sheet:
R
NTC
at 0°C = 27.2k
R
NTC
at 75°C = 1.925k
Q
B
R
S
V
OUT
C
OUT
D
3816 F21
L DCR
INDUCTOR
NTC
Q
T
I
L
V
IN
TG
BG
BSOURCE
I
SENP
I
SENN
I
MAX
LTC3816
SW
+
R
SER
C
IDCR
R
IMAX
R
PAR
Figure 21. Inductor DCR Current Sense Using
NTC Temperature Compensation