Datasheet

LTC2977
86
2977fa
For more information www.linear.com/LTC2977
APPLICATIONS INFORMATION
DCR divided by the number of phases. Care should to be
taken in the layout of the multiphase inductors to keep the
PCB trace resistance from the DC side of each inductor to
the summing node balanced in order to provide the most
accurate results.
Multiphase Design Example
Using the same values for inductance and DCR from
the previous design example, the value for R
CM1
will be
3kΩ for a three phase DC/DC converter if C
CM1
is left at
220nF. Similarly, the value for IOUT_CAL_GAIN will be
DCR/3=3.33mΩ.
Anti-aliasing Filter Considerations
Noisy environments require an anti-aliasing filter on the
input to the LTC2977’s ADC. The R-C circuit shown in
Figure 28 is adequate for most situations. Keep R40 = R50
≤ 200Ω to minimize ADC gain errors, and select a value
for capacitors C10 and C20 that does not add too much
additional response time to the OV/UV supervisor, e.g. τ
≅ 10µs (R = 100Ω, C = 0.10µF).
Figure 28. Antialiasing Filter on V
SENSE
Lines
V
PWR
V
DD33
V
DD33
V
DD25
V
IN_SNS
V
DACP0
V
SENSEP0
V
SENSEM0
V
DACM0
V
OUT_EN0
LTC2977*
0.1µF
0.1µF
V
IN
4.5V < V
IBUS
< 15V
GND
*SOME DETAILS OMITTED FOR CLARITY
ONLY ONE OF EIGHT CHANNELS SHOWN
V
IN
V
OUT
R20
R30
R10
2977 F28
RUN/SS
SGND
V
FB
GND
DC/DC
CONVERTER
LOAD
C10
C20
R50
R40
0.1µF
Figure 27. Multiphase DCR Current Sensing Circuits
R
CM2
R
CM1
R
CM1
R
CM1
R
CM2
R
CM1
/3
DCR
DCR
DCR
L
LL
2977 F27
TO LOAD
SWX3SWX2
SWX1
LTC2977
V
SENSEP1
V
SENSEM1
C
CM2
C
CM1
C
CM1
C
CM2