Datasheet

LTC3861
21
3861fa
For more information www.linear.com/LTC3861
applicaTions inFormaTion
Current Sensing
To maximize efficiency the LTC3861 is designed to sense
current through the inductor’s DCR, as shown in Figure 6.
The DCR of the inductor represents the small amount of
DC winding resistance of the copper, which for most in
-
ductors applicable
to this application, is between 0.3mΩ
and 1mΩ. If the filter RC time constant is chosen to be
exactly equal to the L/DCR time constant of the inductor,
the voltage drop across the external capacitor is equal
to the voltage drop across the inductor DCR. Check the
manufacturer’s data sheet for specifications regarding the
inductor DCR in order to properly dimension the external
filter components. The DCR of the inductor can also be
measured using a good RLC meter.
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
3861 F06a
R
S
ESLL
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
FILTER COMPONENTS PLACED NEAR SENSE PINS
C
F
• 2R
F
≤ ESL/R
S
POLE-ZERO
CANCELLATION
V
LOGIC
V
CC
5V
IN
BG
GND
R
F
C
F
R
F
VINSNS
V
CC
PWM
ISNSPISNSN
LTC3861
GND
(6a) Using a Resistor to Sense Current
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
3861 F06b
DCRL
R1*
INDUCTOR
V
LOGIC
V
CC
5V
IN
*PLACE R1 NEAR INDUCTOR
PLACE C1 NEAR ISNSP, ISNSN PINS
BG
GND
C1*
VINSNS
V
CC
PWM
ISNSPISNSN
LTC3861
GND
R1 • C1 =
L
DCR
(6b) Using the Inductor to Sense Current
Figure 6. Tw o Different Methods of Sensing Current