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TPS63070: TPS63070 Buck-Boost Converter power up problem

Part Number: TPS63070
Other Parts Discussed in Thread: TPS63027, TPS63020

Dear friends,

 

Please help to solve "Power up" problem for TPS63070 adjustable Buck-Boost Converter, that we plan to use in our new design

 

1.    Problem description:

 

The  converter fails to reach the desired output voltage 5.36V upon power up with resistive loads more than 0.7A (the design requirement for the output load is 0..1.5A)

  • For example, after power up, the output voltage sets to 4.86V @ 0.9A load and to 3.55V @ 1.5A load
  • The power good output (PG) remains "Low"

Once the converter starts "NOT OK", reducing the load to the level below 0.7A cause to output voltage rise to desired value 5.36V and to PG output rise to "High". At this stage, the output load can be increased up to 1.5A and converter will continue to operate properly

The same is, if the converter starts "OK" with the output loads below 0.7A -  than, the load can be increased up to 1.5A and converter will continue to operate properly

 

2.    Design spec:

 

Input voltage: 4.75V...5.25V, provided by DC/DC isolated supply 24V/5V, 12W

Output voltage: 5.36V±1.5%

Output current: 0..1.5A

  • Hi,

    It looks like this is the reduced start up current limit implemented in this device. Did you take a look at Fig. 17, 19 and 40 of the datasheet?
  • Hi Sabrina,
    Thank you very much for the answer
    My interpretation for start-up current 0.7 – 0.75A on Fig. 40 was, that it is only in the beginning, when converter starts to build the output voltage – otherwise I need to use additional device to disconnect the 1.5A load during power up and then, after power up will finished, connect the load to converter output
    To overcome this problem – is it possible to use the component feature of selection between two levels of the output voltages. It means, that first start with 2.5V output (current will be less than 0.7A) and then, after PG raised to "High", switch to 5.36V using VSEL and FB2 pins (output current will be increased to 1.5A)?
  • Hi Zeev,

    In my opinion it is possible to use the feature selection feature, and use the PG signal to monitor when to switch.

    As a side note TPS63027 and TPS63020 could eventually suit this spec

  • Hi Sabrina,

    Thank you very much,

    Using TPS63020 is very good advice. It footprint allows direct assembly on our main driver board