LTC3716 Datasheet, PDF (25/28 Pages) Linear Technology – 2-Phase, 5-Bit VID, Current Mode, High Efficiency, Synchronous Step-Down Switching Regulator

LTC3716
APPLICATIO S I FOR ATIO
3) Are the SENSE ^– and SENSE ⁺ leads routed together with
minimum PC trace spacing? The filter capacitors between
SENSE ⁺ and SENSE^– pin pairs should be as close as
possible to the LTC3716. Ensure accurate current sensing
with Kelvin connections at the current sense resistor. See
Figure 10.
4) Does the (+) plate of C_IN connect to the drains of the
topside MOSFETs as closely as possible? This capacitor
provides the AC current to the MOSFETs. Keep the input
current path formed by the input capacitor, top and bottom
MOSFETs, and the Schottky diode on the same side of the
PC board in a tight loop to minimize conducted and
radiated EMI.
5) Is the INTV_CC 1µF ceramic decoupling capacitor con-
nected closely between INTV_CC and the PGND pin? This
capacitor carries the MOSFET driver peak currents. A
small value is recommended to allow placement immedi-
ately adjacent to the IC.
6) Keep the switching nodes, SW1 (SW2), away from
sensitive small-signal nodes. Ideally the switch nodes
should be placed at the furthest point from the
LTC3716.
7) Use a low impedance source such as a logic gate to drive
the PLLIN pin and keep the lead as short as possible.
The diagram in Figure 11 illustrates all branch currents in
a 2-phase switching regulator. It becomes very clear after
studying the current waveforms why it is critical to keep
the high-switching-current paths to a small physical size.
High electric and magnetic fields will radiate from these
“loops” just as radio stations transmit signals. The output
capacitor ground should return to the negative terminal of
the input capacitor and not share a common ground path
with any switched current paths. The left half of the circuit
gives rise to the “noise” generated by a switching regula-
tor. The ground terminations of the sychronous MOSFETs
and Schottky diodes should return to the negative plate(s)
SW1
D1
L1
R_SENSE1
V_IN
R_IN
+
C_IN
V_OUT
+ ^COUT
R_L
BOLD LINES INDICATE
HIGH, SWITCHING
CURRENT LINES.
KEEP LINES TO A
MINIMUM LENGTH.
SW2
D2
L2
R_SENSE2
3716 F11
Figure 11. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator
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