LTC3882-1
50
Rev A
For more information
Figure 25. Inductor DCR Output Current Sense
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
38821 F25
DCR
L
R1*
INDUCTOR
V
CC
V
LOGIC
5V
IN
*PLACE R1 NEAR INDUCTOR
PLACE C1 NEAR I
SENSE
+
, I
SENSE
–
PINS
BG
GND
C1*
VINSNS
V
CC
PWM
I
SENSE
+
I
SENSE
–
LTC3882-1
GND
R1 • C1 =
L
DCR
V
DD33
APPLICATIONS INFORMATION
Figure 26. Discrete Resistor Output Current Sense
waveform across a 2mΩ resistor with a 2010 footprint.
The waveform is the superposition of a purely resistive
component and a purely inductive component. If the
RC time constant is chosen to be close to the parasitic
inductance divided by the sense resistor (L/R), the re-
sultant waveform looks resistive, as shown in Figure 28.
For applications using low maximum sense voltages,
check the sense resistor manufacturer’s data sheet for
information about parasitic inductance. In the absence of
data, measure the voltage drop directly across the sense
resistor to extract the magnitude of the ESL step and the
following equation to determine the ESL:
ESL =
V
ESL(STEP)
∆I
L
•
t
ON
•
t
OFF
t
ON
+ t
OFF
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
38821 F26
V
CC
V
LOGIC
5V
IN
BG
GND
C
F
VINSNS
V
CC
PWM
I
SENSE
+
I
SENSE
–
LTC3882-1
GND
FILTER COMPONENTS PLACED NEAR SENSE PINS
V
DD33
R
F
R
F
R
S
ESL
L
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
C
F
• 2R
F
≤ ESL/R
S
POLE-ZERO
CANCELLATION
If low value (<5mΩ) sense resistors are used, verify that
the signal across C
F
resembles the current through the
inductor, and reduce R
F
to eliminate any large step associ-
ated with the turn-on of the primary switch.
Output Voltage Sensing
Accurate Kelvin sensing techniques should be used
to connect the output voltage differentially back to the
LTC3882-1 V
SENSE
±
pins of the master channel for the best
output voltage regulation at the point of load. These pins
also provide the ADC inputs for output voltage telemetry.
