Hello,
Our customer has questioned the switching frequency is slightly shifted to 700kHz even he sets 650kHz. Although he applies 866k-ohm as temporary on RF against recommended 870k-ohm, the resistance gap is only 0.5%.
Would you let him know if this resistance gap causes the switching frequency? If not please let us know, how comes the switching frequency differences, what is the resistor tolerance against recommended 870k-ohm.
best regards,
The TPS53219A controller uses discrete detection of the RT resistor to select an internal On-time generator scaling to control the switching frequency. The switching frequency is not continuously set based on the analog resistance of the RT resistor. The frequency variation is not due to the 870k-Ohm RT resistor, the same switching frequency would be found for 866kOhms or 862kOhms
700kHz is within the expected tolerance of the 650kHz oscillator setting from 580kHz to 720kHz.
In addition, while the on-time generator attempts to compensate for application variations, D-CAP mode control is, fundamentally, Pulse Frequency Modulation, so some part to part and configuration to configuration variation in frequency is expected.
As for the tolerance of the recommended resistors, TI recommends using a 1% tolerance resistor with a nominal value within 1% of the values recommended in the datasheet.
