LTC3816_15 Datasheet, PDF (23/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

APPLICATIONS INFORMATION
the NTC compensation network. To determine the compo-
nent values, first, select the NTC with room temperature
resistance approximately equal to R_VDCR that has the
smallest temperature coefficient (β constant in the NTC
data sheet. Using an NTC with a higher β constant gen-
erates a less optimal temperature compensation). Next,
calculate the resistances R_PAR and R_SER from the following
equations where the NTC resistances at different tempera-
tures is obtained from the manufacturer’s data sheet.
R_PAR = R_NTC at 25°C
( ) ( ) ( ) ( ) ^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}
Note that the above equations optimize temperature
compensation at hot. At extreme cold temperature, the
temperature compensation is less effective.
With the NTC resistor network, the temperature compen-
sated AVP transfer function becomes:
V_OUT = V_DAC – A_AVP(DCRN) • I_L = V_DAC – A_G(DCRN) • I_L • R_DCR
where A_AVP(DCRN) and A_G(DCRN) are the AVP and DCR gain
using the inductor DCR current sense with NTC temperature
compensation configuration.
A _AVP(DCRN) = A_G(DCRN) •R_DCR
and
A_G(DCRN)
=
R_NTCNET
R_AVPDCRN
C_VDCRN
=
L
R_NTCNET
•
R_DCR
( ) ^R_NTCNET ^{= R}_SER ^{+ R}_PAR ^||R_NTC ^
Figure 11a shows the room temperature AVP DC transfer
curves obtained using inductor DCR current sense with and
without NTC temperature compensation. There is only a
slight difference in the transfer curve at heavy load. Figure
11b shows the AVP transfer curve obtained at 125°C, it
shows the improvement in AVP accuracy with the NTC
resistor network.
Figure 12 shows another easy way to compensate for the
inductor DCR temperature coefficient. In this configura-
tion, a linear PTC resistor is connected from the SW node
to the I_TCFB pin. The PTC thermistor ’s temperature coef-
ficient of 0.411%/°C compensates for the change in DCR
LTC3816
1.02
T_A = 25°C
1.01
1.00
IDEAL + 1.5%
0.99
IDEAL
0.98
0.97
IDEAL – 1.5%
0.96
0.95
0.94
0
WITH NTC
WITHOUT NTC
5 10 15 20 25 30
I_LOAD (A)
3816 F11a
Figure 11a. AVP Transfer Curve Using Vishay
IHLP-5050CE-01 0.33µH (DCR = 1.3mΩ) Inductor
DCR Current Sense with A_G(DCRN) = 1 at T_A = 25°C
1.02
T_A = 125°C
1.01
1.00
IDEAL + 1.5%
0.99
IDEAL
0.98
0.97
IDEAL – 1.5%
0.96
0.95
0.94
0
WITH NTC
WITHOUT NTC
5 10 15 20
I_LOAD (A)
25 30
3816 F11b
Figure 11b. Same Setup as Figure 11a. Improvement
in AVP Accuracy with NTC Temperature Compensation
Network at T_A = 125°C
TG
SW
BG
LTC3816
V_IN
Q_T
Q_B
D
I_L
L DCR
INDUCTOR
LPTC
V_OUT
+
C_OUT
BSOURCE
I_TCFB
–
I_TC
+^AITC
I_SENN
C_VDCRP
R_VDCRP
3916 F12
LPTC: VISHAY TPFT1206 SERIES, 4110ppm/°C
Figure 12. AVP Using Inductor DCR Current Sense
with Linear PTC Temperature Compensation
3816f
23