Datasheet

LTC3816
22
3816f
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 A R and A
R
R
tt
R
AVP SR G SR SEN G SR
VSR
AVPSR
VS
( ) ( ) ( )
•= =
RR VSR
SEN
C
ESL
R
• =
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 A R and A
R
R
AVP DCR G DCR DCR G DCR
VDCR
AVPDCR
( ) ( ) ( )
•= =
RR C
L
R
VDCR VDCR
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
+
Q
B
D
Q
T
V
IN
ESLL
C
OUT
3916 F08
V
OUT
I
L
SENSE RESISTOR
R
SEN
C
VSR
R
AVPSR
TG
BG
BSOURCE
I
TCFB
I
SENN
I
TC
LTC3816
SW
+
–
R
VSR
AITC
+
Q
B
D
Q
T
V
IN
L
C
OUT
3916 F09
V
OUT
I
L
INDUCTOR
DCR
C
VDCR
R
AVPDCR
TG
BG
BSOURCE
I
TCFB
I
SENN
I
TC
LTC3816
SW
R
VDCR
+
–
AITC
Figure 8. AVP Configuration with a Sense Resistor
Figure 9. AVP Configuration with Inductor DCR Current Sense
+
Q
B
D
Q
T
V
IN
L
C
OUT
3916 F10
V
OUT
I
L
INDUCTOR
DCR
NTC
C
VDCRN
R
AVPDCRN
TG
BG
BSOURCE
I
TCFB
I
SENN
I
TC
LTC3816
SW
R
PAR
R
SER
+
–
AITC
Figure 10. AVP with Inductor DCR Current Sense
and NTC Temperature Compensation