LTC3882-1
49
Rev A
APPLICATIONS INFORMATION
R
L1
D1
L1
SW1
R
SENSE1
V
OUT1
C
OUT1
V
IN
C
IN
R
IN
R
L0
D0
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH.
L0
SW0
38821 F24
R
SENSE0
V
OUT0
C
OUT0
Figure 24. High Frequency Paths and Branch Current Waveforms
for most inductors suitable to LTC3882-1 applications, 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 capaci-
tor 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.
Use the nominal or measured value of DCR to program
IOUT_CAL_GAIN (in mΩ). The temperature coefficient
of the inductor’s DCR is typically high, like copper. Again,
consult the manufacturer’s data sheet. The LTC3882-1 can
adjust for this non-ideality if the correct MFR_IOUT_CAL_
GAIN_TC value is programmed. Typically this coefficient
is around 3900ppm/°C.
Resistor R1 should be placed close to the switch node,
to prevent noise from coupling into sensitive small-signal
nodes. Capacitor C1 should be placed close to the IC pins.
An example of discrete resistor sensing of output current is
shown in Figure 26. Previously, the parasitic inductance of
the sense resistor could represent a relatively small error.
New high current density solutions may utilize low sense
resistor values producing sense voltages less than 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. An
RC filter can be used to extract the resistive component
of the current sense signal in the presence of parasitic
inductance. For example, Figure 27 illustrates the voltage
