SLUAAY9 August 2024 TPS543320 , TPS543620 , TPS543820
For this application note, different combinations of R1, RFSEL, and C1 were analyzed and the high voltage and low voltage applied to the SYNC/FSEL pin were recorded. A function generator was used to emulate a clock generator signal, with the output configured to a square wave with an amplitude of 3.3V and the frequency changing depending on the chosen RFSEL. For the sake of evaluation, this circuit was built using through-hole components, however surface-mount versions of these components are easy to find for a traditional application. All results were taken with three EVMs running in parallel. A summary of the results of the various test configurations is shown in Table 3-1.
| RFSEL (kΩ) | FSW (kHz) | R1 (kΩ) | C1 (nF) | Clock Signal Frequency (kHz) | SYNC/FSEL High Voltage (V) | SYNC/FSEL Low Voltage (V) |
|---|---|---|---|---|---|---|
24.3 | 500 | 1.1 | 100 | 600 | 2.64 | -0.160 |
24.3 | 500 | 1.1 | 1 | 600 | 2.56 | -0.120 |
4.99 | 2200 | 1.1 | 100 | 2000 | 1.8 | -0.180 |
4.99 | 2200 | 1.1 | 1 | 1900 | 1.8 | -0.200 |
11.7 | 1000 | 1.1 | 1 | 1200 | 2.28 | -0.200 |
11.7 | 1000 | 0.5 | 1 | 1200 | 2.56 | -0.160 |
11.7 | 1000 | 2 | 1 | 1200 | 2 | -0.160 |
The oscilloscope shots measuring the switching frequency of the TPS543620, the voltage at the SYNC/FSEL pin, and the voltage of the clock signal when the clock is turned off and on are shown in Figure 3-1 through Figure 3-11. For example, The switching frequency of the device when the signal generator is off is shown in Figure 3-1. Channel 1 is the voltage applied to the SYNC/FSEL pin, channel 2 is the switching frequency of the device, and channel 3 is the function generator signal. The device is switching at 514.2kHz, which corresponds to the selected frequency value of the 24.3kΩ RFSEL. The dynamic change of the switching frequency once the signal generator is turned on is shown in Figure 3-2. The switching frequency of the device is recorded to be 599.6kHz, lining up with the values selected for the clock signal, which is set to an amplitude of 3.3V with a frequency of 600kHz. The SYNC/FSEL pin is receiving a signal with a high of 2.66V and a low of -140mV, which is within the specs of the device pin.