LTC3816_15 Datasheet, PDF (36/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

LTC3816
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_IMAX
=


I_LIMIT
+
∆I_L
2


R_DCR
I_IMAX(MIN)
=
29.75A
•
2.085mΩ
9µA
=
6.89k
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_IDCR
=
R_DCR
L
• C_IDCR
=
0.33µH
1.3mΩ • 0.1µF
=
2.538k
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_SER
≈
10
3

R_PAR ||
R_NTC
at
0°C
– R_PAR || R_NTC at 75°C

( ) ( ) ^{– R}_PAR ^{|| R}_NTC ^{at 25°C}
From the NTC data sheet:
R_NTC at 0°C = 27.2k
R_NTC at 75°C = 1.925k
LTC3816
TG
SW
BG
V_IN
Q_T
Q_B
BSOURCE
I_SENP
I_SENN
I_MAX
R_IMAX
I_L
L DCR
INDUCTOR
D
NTC
R_S
V_OUT
+
C_OUT
R_SER
C_IDCR
R_PAR
3816 F21
Figure 21. Inductor DCR Current Sense Using
NTC Temperature Compensation
3816f
36