Texas Instruments Step Down Converter Bypass Mode Low Power Wireless Appl. Evaluation Module TPS62733EVM-726 TPS62733EVM-726 Ficha De Dados

Códigos do produto

TPS62733EVM-726

Test Summary

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4.3

Test Procedure

1. Make sure that the EVM setup is according to

Table 1

and

Figure 1

, and preset the power supply to

3.3 VDC at a current limit of approximately 150 mA.

2. Turn on the input supply and verify the input voltage is approximately 3.3 VDC (DMM 1) and the output

voltage is at approximately 2.1 or 2.3 VDC for TPS62730 or TPS62733, respectively (DMM 2).

3. Look at CH1 and CH2 and verify that the duty cycle is near 70% and the ripple is less than 10-mV

ripple; see

Figure 6

for typical waveforms.

4. Vary the load between 0 and 100 mA [1 k

to 21

(TPS62730) or 1 k

to 23

(TPS62733)].

Observe the change in the switching waveform from PFM with discontinuous ringing to PWM mode. It
may be necessary to change the time scale on the scope to 1 µs/div for light loads. See

Figure 7

and

Figure 8

for various loads. Set the load back to approximately 21

5. Vary the input voltage from 3.3 VDC to 3.9 VDC and back to 2.4 VDC to see the change in duty cycle.

6. Reduce the input voltage from 2.4 VDC to 1.9 VDC and verify that the switcher automatically goes into

bypass mode, disabling the switcher and turning on the internal bypass FET. The output should be the
input voltage minus the IR drop across the pass FET (approximately 2

). The STAT pin should go to

the high-impedance state with R1 pulling it to the output voltage. Conditions for the capture of

Figure 9

were: CH2 moved to the J7 (STAT) header relative to ground, 1 V/div, dc-coupled, the time scale set
to 50 µs/div (a slower time scale may be required, depending on power-supply decay), single-
sequence trigger on CH2, and input power removed. The figure shows the switch node going into
PFM, then disabling switching, and then indicating bypass mode by R1 pulling the STAT pin up to the
output voltage (approximately 2.2 VDC).

CAUTION

The following step disables the buck converter and switches the input voltage
to the output. Make sure not to exceed the maximum system input voltage in
this step or the later steps that place the JP1 shunt in the bypass position.

7. Move the shunt on jumper JP1 from the ON position to the Bypass position. Notice that this action

disables the switcher and switches the input voltage to the output via the bypass switch. The output
should be the input voltage minus the IR drop across the pass FET (approximately 2

). The STAT pin

should go to the high-impedance state with R1 pulling it to the output voltage. Move the shunt on
jumper JP1 to the ON position.

8. For steps 9 through 13, one can view the figure and determine the oscilloscope setup.

9. See

Figure 10

for the transition from converter switch mode to bypass mode by pulling the ON/BYP pin

low.

10. Remove the bypass jumper to see the transition from bypass mode to converter switch mode; see

Figure 11

11. See

Figure 12

for typical hot-plug power up.