PM6652 datasheet(39/53 Pages) STMICROELECTRONICS

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PM6652

Device description

Doc ID 16867 Rev 5

39/53

8.10.6

Overcurrent protection

The PM6652 controller can limit the maximum load current by skipping one or more

switching cycles if the valley current limit is detected. The current limit sensing is

independent from the current sensing for droop and IMON functions. Basically, the voltage

drop sensed between the PGND and PHASE pins, when the low-side MOSFET is on, is

compared with the voltage across the external RILIM resistor. The following equation helps to

program the valley current limit value (see

Figure 41):

Equation 20

Figure 41.

Valley current limit circuitry

The maximum programmable voltage on pin ILIM is 3.5 V (typ.); as a consequence the

maximum effective RILIM resistor is about 700 kΩ.

If, starting from the previous equation, a higher resistance is required the resulting low-side

MOSFET ON-resistance is not adequate for the designed application.

The maximum available load current, with the valley current limit technique, is equal to:

Equation 21

i.e. the maximum available current is the sum of the valley current limit value plus the half of

the inductor current ripple. The valley current limit is sensed each switching cycle, during

TOFF time (when the low-side MOSFET is turned on). This fault protection is not latched but

the typical behavior is the one shown in

Figure 42:

()

PHASE

PGND

ILIM

−

⋅

VCL

MAX

LOAD

∆

⋅

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