SLVAFD6 July   2022 TPS564247 , TPS565242

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Analysis of the Floating-Input Pre-bias Output Operation
    1. 2.1 Analysis of FCCM Device
    2. 2.2 Analysis of PSM Device
  5. 3Experimental Verification
    1. 3.1 FCCM device
      1. 3.1.1 Bias Voltage > Target
      2. 3.1.2 Bias Voltage < Target
    2. 3.2 PSM device
      1. 3.2.1 Bias Voltage > Target
      2. 3.2.2 Bias Voltage < Target
  6. 4Summary
  7. 5References

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.

Table 3-2 Test Result of Vbias<Vtarget in FCCM Device
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
GUID-20220623-SS0I-L0LG-VSXQ-LRZ4QKSKDCN3-low.png Figure 3-3 Test Waveform of Vbias<Vtarget in FCCM Device