SC415_08 datasheet(22/30 Pages) SEMTECH

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SC415

Layout Guidelines

As with any switch-mode converter, and especially a

dual-channel converter, a good pcb layout is essential for

optimum performance. The following guidelines should

be used for pcb layout.

Placement

Note that the pins on the IC are arranged in four groups,

i.e. Side1 Power, Side2 Power, Side1 Analog, and Side2

Analog, as shown below.

LX1

BST1

VDD1

DL1

EN1

SS1

LX2

BST2

VDD2

DL2

EN2

SS2

GND

(PAD)

SC415

Side 1

Power/Gate

Drive

Side 2

Power/Gate

Drive

Side 1

Analog

Side 2

Analog

Figure 17

For placement, power devices for side1 should be grouped

together near the gate drive pins for side1 (pins 23-24 and

1-8). Power devices for side2 should be grouped together

near the gate-drive pins for side2 (pins 15-20).

The feedback and VOUT sense components should

be located near the FBx/VOUTx pins. This includes the

feedback resistors and capacitors if used.

Ground Connections

When doing placement, be aware that there are four

grounds.

Power ground for Side1

Power ground for Side2

Analog ground for Side1

Analog ground for Side2

Note that grounds (1) and (2) are high-current and contain

high noise. These grounds carry the DL gate drive current

as well as the high switching current through the MOSFETs

and low-side diode. It is important to note that the SC415

has only one power ground pin (PAD, pin 25), which must

drive DL for both side1 and side2. As such, the low-side

MOSFET and diode will need to be near the IC.

Grounds (3) and (4) are low-current and intended for low-

noise VOUT/FB ripple sensing. Note that there is only one

analog ground pin (RTN, pin 9) which shared between

sides 1 and 2.

Proper connection between the grounds is needed

for good operation. Generally, all ground connections

between the power components and the SC415 should

be short and direct, without vias where possible. Each

side has significant high-current switching in the ground

path, moving between the input capacitors, the low-

side MOSFET, the low-side diode if used, and the output

capacitors.

Moreover, each side has significant high-

current pulses to/from the ground PAD, created by the DL

drive to the low-side MOSFETs. The DL gate-drive current

peaks can be 2 amps or more, with fast switching. As such

the ground connection between the low-side MOSFETs

and the ground PAD should be as short and wide as

practical.

Note that the ground PAD, which is the return path for

the high-noise DL drive current, is not accessible on the

top layer of the pcb, due to the other pins. The ground

Applications Information (continued)

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