Data Sheet

TB67S249FTG

2017-08-18

OSCM oscillator frequency (chopping frequency) calculation

OSCM oscillator frequency can be calculated by using the external component values (ROSC and COSC), and the formula

is shown below. (COSC is fixed to 270 pF.)

fOSCM = 4.0 x ROSC

(-0.8)

COSC and ROSC are external components to set the oscillator frequency. When adjusting the oscillator frequency with

components, it is recommended to fix COSC to 270 pF and change the constant number of ROSC.

Moreover, the relation between the chopping frequency for constant current PWM (fchop) and the OSCM oscillator

frequency (fOSCM) is as follows;

fchop = fOSCM / 16

For normal operation, setting the frequency in the range of 50 kHz to 70 kHz and adjusting suitably as needed is

recommended

When the chopping frequency is set high, the current ripple will be smaller, which will lead to a higher reproducibility of a

waveform. However, the chopping frequency per unit time is increased and so the gate loss and the switching loss of the

integrated MOSFET will be larger, which will lead to an additional heat generation. On the other hand, when the chopping

frequency is set low, the current ripple will be larger but the heat generation is reduced. Please set the frequency according

to the usage conditions and environment.