SLVAFD6 July 2022 TPS564247 , TPS565242
3.1.2 Bias Voltage < Target
In the experiment, the target output voltage is 5 V, bias output is 4.95 V. It should be noticed that TPS565247 has the large duty operation function. From the data sheet, if Vin/Vbias< 1.6, and Vbias< target, the frequency will smoothly reduce with the ratio Vin/Vbias, the minimum switching frequency is limited about 200 KHz. Based on bias output voltage and Equation 8, even though with normal frequency (570 KHz), Vin will not exceed 1.6 Vbias. So the switching frequency will reduce to minimum 200 KHz, as shown in Figure 3-3. From the test result in Table 3-2, the calculated input voltage based in Equation 8 is 5.055 V, very closed to measured value.
| Test device | Vbias | Fsw | Toff_min | Vin from eq(5) | Vin measured |
|---|---|---|---|---|---|
| TPS565247 | 4.95 V | 200 KHz | 104 ns | 5.055 V | 5.08 V |
Figure 3-3 Test Waveform of
Vbias<Vtarget in FCCM Device