LTC3816_15 Datasheet, PDF (22/44 Pages) Linear Technology – Single-Phase Wide VIN Range DC/DC Controller for Intel IMVP-6/IMVP-6.5 CPUs

LTC3816
APPLICATIONS INFORMATION
where A_AVP(SR) is the AVP gain with sense resistor con-
figuration and A_G(SR) is the sense resistor gain:
A_AVP(SR) = A_G(SR) •R_SEN
and
A_G(SR)
=
R_VSR
R_AVPSR
tt
R_VSR
•
C_VSR
=
ESL
R_SEN
Figure 9 shows the AVP configuration with current sense
implemented using the inductor DCR. The AVP DC transfer
function is:
V_OUT = V_DAC – A_AVP(DCR) • I_L = V_DAC – A_G(DCR) • I_L • R_DCR
where:
A _AVP(DCR) = A_G(DCR) •R_DCR
and
A_G(DCR)
=
R_VDCR
R_AVPDCR
R_VDCR
•
C_VDCR
=
L
R_DCR
Temperature Compensated Active Voltage
PositionING (AVP) With Inductor DCR
The inductor DCR AVP configuration improves the regula-
tor efficiency by eliminating the power losses associated
with a sense resistor. However, without proper temperature
compensation, the positive temperature coefficient of the
inductor DCR, 0.39%/°C, may compromise the output volt-
age accuracy. As the temperature of the inductor rises, its
DCR value increases, resulting in a greater V_OUT droop rate
(higher AVP gain). To compensate for the DCR temperature
shift, replace the resistor R_VDCR in Figure 9 with an NTC
resistor placed as close as possible to the inductor. Ideally,
the NTC resistor should have the same temperature as the
inductor. As temperature increases, the NTC resistance
drops, resulting in a reduction in the AITC amplifier voltage
gain. This compensates for the increase in DCR resistance
and maintains the AVP gain. The NTC resistor, however, is
highly nonlinear and must be linearized. Figure 10 shows
TG
SW
BG
LTC3816
BSOURCE
I_TCFB
–
I_TC
+^AITC
I_SENN
V_IN
Q_T
L
Q_B
D
C_VSR
I_L
ESL R_SEN
SENSE RESISTOR ₊
V_OUT
R_AVPSR
C_OUT
R_VSR
3916 F08
Figure 8. AVP Configuration with a Sense Resistor
TG
SW
BG
LTC3816
BSOURCE
I_TCFB
–
I_TC
+^AITC
I_SENN
V_IN
Q_T
Q_B
I_L
L DCR
INDUCTOR
D
R_AVPDCR
V_OUT
+
C_OUT
C_VDCR R_VDCR
3916 F09
Figure 9. AVP Configuration with Inductor DCR Current Sense
TG
SW
BG
LTC3816
BSOURCE
I_TCFB
–
I_TC
+^AITC
I_SENN
V_IN
Q_T
Q_B
I_L
L DCR
INDUCTOR
D
R_AVPDCRN NTC
V_OUT
+
C_OUT
C_{VDCRN RSER}
R_PAR
3916 F10
Figure 10. AVP with Inductor DCR Current Sense
and NTC Temperature Compensation
3816f
22