JAJSKF5 データシート

JAJSKF5D September 2021 – November 2024 TPSM82864A , TPSM82866A

PRODMIX

7.3.1 Power Save Mode

As the load current decreases, the device seamlessly enters power save mode (PSM) operation. In PSM, the converter operates with a reduced switching frequency and a minimum quiescent current to maintain high efficiency. Power save mode is based on a fixed on-time architecture, as shown in Equation 1. The inductance used in the RCF package using MagPack technology is 200 nH typical where the inductance used in the RDJ and RDM packages is 220 nH typical.

Equation 1.

t_{O N} = \frac{V_{O U T}}{V_{I N} \times f_{S W}}

For very small output voltages, an absolute minimum on time of approximately 50ns is kept to limit switching losses. The operating frequency is thereby reduced from the nominal value, which keeps efficiency high. The switching frequency in PSM is estimated as:

Equation 2.

f_{P S M} = \frac{2 \times I_{O U T}}{{t_{O N}}^{2} \times \frac{V_{I N}}{V_{O U T}} \times \frac{V_{I N} - V_{O U T}}{L}}

The load current at which PSM is entered is at one half of the ripple current of the inductor and can be estimated as:

Equation 3.

I_{L o a d (P S M - e n t r y)} = \frac{V_{I N} \times t_{O N}}{2} \times \frac{1 - \frac{V_{O U T}}{V_{I N}}}{L}

In power save mode, the output voltage rises slightly above the nominal output voltage. This effect is minimized by increasing the output capacitance.