PM6652 datasheet(32/53 Pages) STMICROELECTRONICS

32 / 53 page

Device description

PM6652

32/53

Doc ID 16867 Rev 5

The previous equation also shows the frequency dependence of the DCR current sensing

technique. During load variation the sensed DCR can also increase, if the time constant

matching is not adequate; in order to avoid this situation the following equation must be

verified:

Equation 10

Figure 31 shows the VCORE load transient response when Equation 10 is not verified

whereas in

Figure 32 the load transient response shows a better time constant matching.

If a thermal compensation is required in order to compensate for the inductor's DCR

variation, due to a temperature increase, RB is replaced by a complete network, based on

an NTC (negative temperature coefficient) thermistor (Rn).

Figure 33 shows an example of

an NTC-based thermal compensation network (Rs, Rp and Rn). The resulting RB1

equivalent resistance and NTC network attenuation are:

Equation 11

and the time constant due to the CA capacitor may be computed as follows:

Equation 12

In the PM6652 the CSNS and VOUT inputs are high-impedance pins so a very small

leakage current can be measured, in the range of 50 nA to 100 nA. This leakage current,

sourced by CSNS, is multiplied by the equivalent resistance measured across the CA

DCR

≥

Figure 31.

L >

Figure 32.

L <

()

NTC

)

(

()

⋅

PM6652 Datasheet(PDF) 32 Page - STMicroelectronics