I am looking to use UCD7242 with low frequency range from 20-50 kHz according to these low frequency the values of L and C power stage , will be big let’s say L=200uH and C=300uF. So, Can I use this device (UCD7242) with these values of this low frequency? Also, Can I connect the PWM input to this device directly to the PWM output of eZDSP F28335, I mean without using any buffer circuit.
Yes, you can use the UCD7242 down at 20-50kHz, but you will run into some issues when operating at such a low frequency. First, you would liklely want to increase the value of the boostrap capacitors from 0.22uF to about 1uF so that they stay charged during the long on-times. Second, when operating at such low frequency, the current sense output may no longer report the accurate output current. The current sense circuitry requires activity on the PWM input pin at least every 5us to provide accurate output current reporting. If there is no PWM edge in about 5us, the chip assumes that power conversion has stopped and will report no current. This sets the lowest operating frequency to 200kHz. To be safe, the datasheet specifies a lower limit of 300kHz. If you can live without the current sense information, then the chip can be used at low frequencies. Third, yes, the value of the required inductor and output capacitors get quite large at the low frequency.
The PWM input is a 3.3V logic level input. You should be able to drive it from the F28335 without a buffer.
Joseph G. RenauerPower TechnologistTexas Instruments
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