ISL6277A

35

FN8322.0

December 19, 2012

5

VR_HOT_L

Follow AMD recommendations. Placement of the pull-up resistor near the IC is recommended.

6

SVD

Use good signal integrity practices and follow AMD recommendations.

7

VDDIO

Use good signal integrity practices and follow AMD recommendations.

8

SVT

Use good signal integrity practices and follow AMD recommendations.

9

ENABLE

No special considerations.

10

PWROK

Use good signal integrity practices and follow AMD recommendations.

11

IMON

Place the IMON resistor close to this pin and keep a tight GND connection.

12

NTC

The NTC thermistor must be placed close to the thermal source that is monitored to determine Core thermal

throttling. Placement at the hottest spot of the Core VR is recommended. Additional standard resistors in the

resistor network on this pin should be placed near the IC.

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

TABLE 14. LAYOUT CONSIDERATIONS FOR THE ISL6277A CONTROLLER (Continued)

ISL6277A PIN

SYMBOL

LAYOUT GUIDELINES

Vo

ISEN3

L3

ISEN2

ISEN1

L2

L1

Phase1

Phase2

Phase3

GND

INDUCTOR

CURRENT-SENSING TRACES

VIAS

INDUCTOR

CURRENT-SENSING TRACES