JAJSQX8 august 2023 TPSM843A26E
PRODUCTION DATA
When the external clock is present, the device synchronizes the switching frequency to the clock. Any time the external clock is not present, the device defaults to the internal PWM oscillator frequency.
If the device starts up before an external clock signal is applied, then the internal PWM oscillator frequency is set by the RFSEL resistor according to Section 7.3.5.3. The device switches at this frequency until the external clock is applied or anytime the external clock is not present.
If the external clock is applied before the device starts up, then the RFSEL resistor is not needed. The device then decodes the external clock frequency and selects an internal PWM oscillator frequency.
External Sync Clock Frequency (kHz) | Decoded Internal PWM Oscillator Frequency (kHz) |
---|---|
400 – 600 | 500 |
600 – 857 | 750 |
857 – 1200 | 1000 |
1200 – 1810 | 1500 |
1810 – 2640 | 2200 |
The thresholds for the external SYNC clock frequency ranges have approximately a ±5% tolerance. If the external clock frequency is within that tolerance range, it is possible for the internal PWM oscillator frequency to be decoded as either the frequency above or below that threshold. Because the internal frequency is what is used in case of the loss of the synchronization clock, TI recommends that the output LC filter and ramp selection are chosen for stability for either frequency. Table 7-3 shows the tolerance range of the decode thresholds. If the external clock is to be within any of these ranges, TI recommends to design the converter to ensure converter stability for both possible internal PWM oscillator frequencies.
Minimum (kHz) | Typical (kHz) | Maximum (kHz) |
---|---|---|
570 | 600 | 630 |
814 | 857 | 900 |
1140 | 1200 | 1260 |
1736 | 1810 | 1884 |