ISL6277

FN8270 Rev 1.00

Page 34 of 37

Mar 8, 2012

13

ISEN3

GND. Place Cisen capacitors as close as possible to the controller and keep the following loops small:

1. Any ISEN pin to another ISEN pin

2. Any ISEN pin to GND

The red traces in the following drawing show the loops to be minimized.

14

ISEN2

15

ISEN1

16

ISUMP

Place the current sensing circuit in general proximity of the controller.

Place capacitor Cn very close to the controller.

Place the NTC thermistor next to Core VR Channel 1 inductor so it senses the inductor temperature correctly.

Each phase of the power stage sends a pair of VSUMP and VSUMN signals to the controller. Run these two

signals traces in parallel fashion with decent width (>20mil).

IMPORTANT: Sense the inductor current by routing the sensing circuit to the inductor pads. If possible, route the

traces on a different layer from the inductor pad layer and use vias to connect the traces to the center of the

pads. If no via is allowed on the pad, consider routing the traces into the pads from the inside of the inductor.

The following drawings show the two preferred ways of routing current sensing traces.

17

ISUMN

18

VSEN

Place the filter on these pins in close proximity to the controller for good coupling.

19

RTN

20

FB2

Place the compensation components in general proximity of the controller.

21

FB

22

COMP

23

PGOOD

No special consideration.

24

BOOT1

Use a wide trace width (>30mil). Avoid routing any sensitive analog signal traces close to or crossing over this

trace.

25

UGATE1

These two signals should be routed together in parallel. Each trace should have sufficient width (>30mil). Avoid

routing these signals near sensitive analog signal traces or crossing over them. Routing PHASE1 to the Core VR

Channel 1 high-side MOSFET source pin instead of a general connection to PHASE1 copper is recommended for

better performance.

26

PHASE1

TABLE 14. LAYOUT CONSIDERATIONS FOR THE ISL6277 CONTROLLER (Continued)

ISL6277 PIN

SYMBOL

LAYOUT GUIDELINES

Vo

ISEN3

L3

Risen

ISEN2

ISEN1

L2

L1

Risen

Risen

Phase1

Phase2

Phase3

Ro

Ro

Ro

GND

Cisen

Cisen

Cisen

Cvsumn

Vsumn

INDUCTOR

CURRENT-SENSING TRACES

VIAS

INDUCTOR

CURRENT-SENSING TRACES