PM6652 datasheet(26/53 Pages) STMICROELECTRONICS

26 / 53 page

Device description

PM6652

26/53

Doc ID 16867 Rev 5

Equation 1

where KOSC is a constant value (140 ns typ.) and τ is the internal propagation delay (40 ns

typ.).

This leads to a nearly constant switching frequency, regardless of input and output voltages.

When the output voltage goes lower than the internal programmed voltage (see

Section 8.5:

Droop function for details), the on-time one-shot generator directly drives the high-side

MOSFET for a fixed on-time, allowing the inductor current to increase; after the on-time, an

off-time phase, in which the low-side MOSFET is turned on, follows.

If the DPRSLPVR control pin is set low, the low-side MOSFET is turned off only when the

output voltage becomes lower than the programmed value again, and a new cycle begins. In

this working mode the switching frequency is almost load independent, as shown below.

Refer to

Section 8.4: Differential remote sensing section for details about the light load, high-

efficiency algorithm.

The duty cycle of the buck converter, in steady-state conditions, is given by:

Equation 2

The switching frequency is therefore calculated as:

Equation 3

where:

Equation 4

can be set by varying the external resistor ROSC, placed between the VIN and VOSC pin.

RINT is the integrated switching frequency programming resistor (typ. 17 kΩ).

The resulting switching frequency is theoretically independent from battery and output

voltage; actually the conduction losses due to MOSFET ON-resistance, inductor DCR and

PCB traces can slightly influence the programmed value.

OSC

OUT

OSC

OUT

OSC

OUT

OSC

OUT

⋅

≅

OSC

INT

OSC

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