INDUCTOR DCR CURRENT SENSING

Co

Lx

VIN

Rs(DCR)

+

Cx

Rx

Control

logic

&

Driver

DRVH

DRVL

CSP

CSN

Inductor

Co

Lx

VIN

Rs(DCR)

+

Cx

Rx

Control

logic

&

Driver

DRVH

DRVL

CSP

CSN

Inductor

Rc

(

)

Lx

Cx

Rx

Rc

Rs

´

=

P

(17)

I

OCL(PEAK) + VOCL

1

Rs

Rx ) Rc

Rc

(18)

TPS51222

SLUS908 – JANUARY 2009............................................................................................................................................................................................... www.ti.com

To use inductor DCR as current sensing resistor (Rs), the configuration needs to change as below. However, the

equation that must be satisfied is the same as the one for the resistor sensing.

Figure 44. Inductor DCR Current Sensing

Figure 45. Inductor DCR Current Sensing With Voltage Divider

TPS51222 has a fixed V(OCL) point (60 mV). In order to adjust for DCR, a voltage divider can be configured a

described in Figure 45.

For Rx, Rc and Cx can be calculated as shown below, and overcurrent limitation value can be calculated as

follows:

Figure 46 shows the compensation technique for the temperature drifts of the inductor DCR value. This scheme

assumes the temperature rise at the thermistor (RNTC) is directly proportional to the temperature rise at the

inductor.

28

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