SC2597

10

Critical Layout Guidelines

Bias and Reference Capacitors:

A 1μF capacitor must be placed as close as possible to the

IC and connected between pin 6 (VDD) and the ground

plane.

A 0.1μF capacitor must be placed as close as possible to

the IC and connected between pin 4 (VREF) and the

ground plane. The user has an option to add this capaci-

tor to the circuit but it is recommended to layout with a

capacitor place holder.

VDDQ Reference Capacitor:

An R-C filter from the supply used for VDDQ consisting of

a 100 Ω resistor and a 0.1μF capacitor should be placed as

close as possible to the IC and connected between pin 5

(VDDQ) and the ground plane, as shown on page 6.

VTT and VIN Capacitors:

Since SC2597 provides both sink and source capabilities,

the loop impedance through the input and VTT capacitors

plays an important role in circuit stability. Figure 4 shows

both sink and source current loops. Close attention to

board layout is needed to reduce ESL in these loops.

During a bode plot measurement for the sourcing current

loop, an injected small AC signal flows around the loop

from C

IN

to Q

T

through C

VTT

and then returns to C

VIN

through

the ground plane. Therefore, it is recommended to keep

the C

IN

and C

VTT

capacitors as close as possible to reduce

the ESL impedance between them. Similarly in the sinking

PG ND on top and bottom layers

C6

C7

C4

C5

Route VTT sense

trace on inner layer

VTT copper pour on top

and bottom layers

VIN copper pour on top

and/or bottom layer

C3

C2

C1

C 4,C5 shown located

on bottom side

Figure 3 — Component Placement and Layout

current loop, an injected small AC signal flows from C

VTT

through Q

B

and then returns to C

VTT

through the GND

plane. Therefore, it is recommended to keep ESL small for

this loop. Balancing the ESL of those loops gives the best

case for stability.

VIN

VTT

GN D

S ourcing C urrent

Loop

VIN

VTT

GN D

S inking C urrent Loop

Figure 4 — Small AC Signal Current Loops

Figure 2 — Gain and Phase Bode Plot

Fc = 810KHz, PM = 36 degree at 1A Source