LTC3882_15 Datasheet, PDF (47/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

APPLICATIONS INFORMATION
LTC3882
V_IN
R_IN
C_IN
SW1
L1
R_{SENSE1 VOUT1}
D1
C_OUT1
R_L1
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH.
SW0
D0
L0
R_{SENSE0 VOUT0}
C_OUT0
R_L0
3882 F24
Figure 24. High Frequency Paths and Branch Current Waveforms
A useful CAD technique is to make separate ground
nets and use a 0Ω resistor to connect them to system
ground.
8. Place all small-signal components away from high
frequency switching nodes. Place decoupling capaci-
tors for the LTC3882 immediately adjacent to the IC.
9. A good rule of thumb for via count in a given high cur-
rent path is to use 0.5A per via. Be consistent when
applying this rule.
10. Copper fills or pours are good for all power connec-
tions except as noted above in rule 3. Copper planes
on multiple layers can also be used in parallel. This
helps with thermal management and lowers trace
inductance, which further improves EMI performance.
Output Current Sensing
The I_SENSE+ and I_SENSE– pins are high impedance inputs to
internal current comparators, the current-sharing loop and
telemetry ADC. The common mode range of the current
sense inputs is approximately 0V to 5.5V. Continuous linear
operation is provided throughout this range. Maximum
differential current sense input (I_SENSE+ – I_SENSE–) is 70mV,
including any variation over temperature. These inputs
must be properly connected in the application at all times.
To maximize efficiency at full load the LTC3882 is designed
to sense current through the inductor’s DCR, as shown in
Figure 25. The DCR of the inductor represents the small
amount of DC winding resistance of the copper, which
for most inductors suitable to LTC3882 applications, is
between 0.3mΩ and 1mΩ. If the filter RC time constant is
3882f
For more information www.linear.com/LTC3882
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