Datasheet

LTC3829
15
3829fa
For more information www.linear.com/LTC3829
APPLICATIONS INFORMATION
1mΩ and the peak sense voltage can be as low as 20mV.
In addition, inductor ripple currents greater than 50%
with operation up to 1MHz are becoming more common.
Under these conditions the voltage drop across the sense
resistor’s parasitic inductance is no longer negligible. A
typical sensing circuit using a discrete resistor is shown in
Figure 2a. In previous generations of controllers, a small
RC filter placed near the IC was commonly used to reduce
the effects of capacitive and inductive noise coupled in
the sense traces on the PCB. A typical filter consists of
two series 10Ω resistors connected to a parallel 1000pF
V
IN
V
IN
INTV
CC
BOOST
TG
SW
BG
PGND
FILTER COMPONENTS
PLACED NEAR SENSE PINS
SENSE
+
SENSE
–
SGND
LTC3829
V
OUT
3829 F02a
C
F
• 2 • R
F
≤ ESL/R
S
POLE-ZERO
CANCELLATION
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
R
S
ESL
C
F
R
F
R
F
V
IN
V
IN
INTV
CC
BOOST
TG
SW
BG
PGND
ITEMP
R
NTC
*PLACE C1 NEAR SENSE
+
,
SENSE
–
PINS
**PLACE R1 NEXT TO INDUCTOR
INDUCTOR
OPTIONAL
TEMP COMP
NETWORK
DCRL
SENSE
+
SENSE
–
SGND
LTC3829
V
OUT
3829 F02b
R1**
R2C1*
R
P
R
S
R1
||
R2 × C1 =
L
DCR
R
SENSE(EQ)
= DCR
R2
R1 + R2
(2a) Using a Resistor to Sense Current
(2b) Using the Inductor DCR to Sense Current
Figure 2. Two Different Methods of Sensing Current
capacitor, resulting in a time constant of 20ns. This same
RC filter, with minor modifications, can be used to extract
the resistive component of the current sense signal in the
presence of parasitic inductance. For example, Figure 3
illustrates the voltage waveform across a 2mΩ sense
resistor with a 2010 footprint for the 1.2V/15A converter
operating at 100% load. The waveform is the superposi-
tion of a purely resistive component and a purely inductive
component. It was measured using two scope probes
and waveform math to obtain a differential measurement.
Based on additional measurements of the inductor ripple