IR3721 datasheet(11/16 Pages) IRF

11 / 16 page

IR3721

DATA SHEET

Page 11 of 16

www.irf.com

09/15/08

LAYOUT GUIDELINES

Refer to figures 7 through 11 for guidance laying out

the IR3721. These guidelines also apply to resistive

current sensing. The following guidelines will

minimize sources of noise and error, which is

required because millivolt level signals correspond to

amps of inductor current.

1. Place the capacitor Ccs2 close to the VO and

VCS pins of the IR3721. Treat VO and VCS as a

differential signal pair back to the IC as shown in

the elliptical area designated #1 of figure 8.

2. Sense the inductor (or shunt) Kelvin style at its

terminals. Route the leads back as a differential

pair. Refer to area #2 of figure 8.

3. Route signal VOUT back to the IC VK pin on its

own dedicated trace. Refer to area #3 of figure 8.

4. Place the thermistor near the inductor. Refer to

area #4 of figure 8. Route the thermistor leads

back to the rest of the network using differential

traces. Mount the rest of the thermistor network

consisting of Rs, Rp, and R1 close to the IC.

5. Use an isolated dedicated ground plane

connected only to components associated with

the IR3721 that connect to GND as shown in

figure 9. Connect this dedicated ground plane at

one location only to the ground of the monitored

voltage. The thermally relived via in figure eight

illustrates this connection.

6. Bypass IC VDD pin 5 to GND pin 4 with a high

quality 0.1 μF ceramic capacitor. Refer to area #6

of figure 8.

7. Bypass the IC VK pin to GND with a high quality

0.1 μF ceramic capacitor. Refer to area #7 of

figure 8.

DI_FILT

GND

C_VK

0.1uF

Rth

R_DI_FILT

C_DI_FILT

VOUT

IR3721

GND_1

VCC

GND_4

GND_3

VCC_1

C_VDD

0.1uF

Rcs1

Ccs1

VOUT

VDD

Rcs2

Ccs2

Figure 7 Example schematic

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