Is an error in FUNCTIONAL BLOCK DIAGRAM of the TPS53313 datasheet

I believe you are correct, the high side FET should be connected to VIN.  You should be able to get 1.8 V at lower input voltage than 7.4 V.  C15 is the BOOT capacitor.  It does not change the voltage of BP7.  BP& is generated from VIN by an internal LDO.  Can you post your actual schematic and some waveforms showing proper operation at VIN  > 7.4 V and improper operation at VIN < 7.4 V?

  Thanks John.  Some more test is made.the results are:

       1. The test circuit is similar to TPS53313EVM-078, the output voltage is set to 1.8V,  the operation mode set to skip mode.  the input power  set to 5V,  the output laod is 10om. the output is like a UNDERVOLTAGE PROTECTION, 18ms period wave, top voltage is about 1.4V, duration 7ms, bottom is 0 voltage. At that time,

the voltage at BP7 is a square wave, top 3V 11ms ,  bottom 2.4v 7ms .

    2.  use an 1Kom resistor to connect BP7 and Vin, it worked well.

    3.  I found When Voltage of BP7 greater than 4.2V, it worked well.

    4. question: when Vin less than 6V, just connect BP7 to Vin directly, is it OK?

       When Vin below 7.4V,  what rang of the  value of the resistor witch is used to connect BP7 and Vin is ok .

       Using this resistor,the circuit  is reliable. 

   5. In Datasheet,  just figure 3 show 5V input is ok, The Vin of  EVM  is 8V to 14V

       no word tell how to use the TPS53313 at 5V Vin. and how you get figure 3?

   Hongxing Zhu

 Beijing Infotronix Co. Ltd.,  zhu@pcm.cn

Let me see if I can direct someone to answer your questions.

HI Hongxing,

Can you send your schematic?

Also, send a waveform of Vbst - SW node with 5VIN VIN.

regards

Mingyue

                       The  Test  about  TPS153313 

1. Description about the application

 Input voltage: 5V

Output1: 3.3V  about 4A is needed;

Output2：-1.8V  about 3A is needed.

 5344.p1.tif

1. Design schematic:

3.3V output schematic:

 1715.p2.tif

-1.8V schematic:

 0654.p3.tif

1. Debug step1:

Part of -1.8V output

 5148.p4.tif

Problem: at 5V input, the voltage of BP7 is not correct, output wave from 0 to -1.4V;

        When input voltage go above 7.4V, the output become normal, even

        Decrease the voltage to 5V, the output is also normal.

Solution: using 1KΩ to connect BP7 with Vin, it become working normal.

1. Step2:

Input 5V and -1.8V, output from GND and -1V8, the schematic become:

The test result is similar to step1.

Connecting BP7 and Vin with 1KΩ resistor , it worked normal.

0250.p5.tif 

1. Step 3:

Debug 3.3V output

It is very lucky,  it worked well.

1. The deference of two part circuit:

The Volate of BP7 of 3.3V output part is:

When Vin<6V,  VBP7=Vin,

When Vin>6V,  VBP7=6.01V.

   The Volate of BP7 of1.8V output part is:

When Vin<6V,  VBP7 is in square wave,

When Vin>6V,  VBP7=6.01V.

Connect BP7 and Vin with 1kΩ, it become normal.

Because it is new design of us, may some mistake inside,   

We will test the circuit board future more, to find out the reason.

I hope it will not take too much your time, my be it just our mistake.

Hongxing Zhu

Beijing Infotronix

Hongxing,

You didn't mention your application is "-1.8V", You are using this device as a buck-boost configuration.

In the -1.8V schematic, why your 5VIN connected to GND?

In the failure case, Can you measure the voltage on the BP7? 

Regards

Mingyue

Hello Mingyue:

Because  the "-1.8V" application is out of Datasheet, so I did not mention.

When I found my "-1.8V" did not work well, I changed it to work as +1.8V output,

it is meet the application rang of datasheet. In order to avoid waste your time, I just discussed

within the rang of datasheet

I checked my 5VIN, it be not connected directly to GND, through a capacitor, it connected to GND.

In failure case, the BP7 is wave from 3V to 2.4V, the period is about 18ms, it seems low voltage protection.

2548.-1.8.tif,

Thank you very much, I have a good 5V to 3.3V board, more board will test, for +1.8V output and -1.8V output. 

It will report later.

Hongxing

Hello Friends:  

 I found the mistake, the PG pull up resistor should be 51K, but we make a mistake, an 51Ω

was in the place, it used too much current from BP7. now it is OK.

     The TPS53313 is the first time used by us. In the document  "Using the TPS53313EVM-078"  , the input rang is

from 8V to 14V. In  the table 3 in datasheet, the Vin input rang is 10.8 to 13.2V.  So I do not know what will happened  when Vin rang from 4.5 to 8V.

     I think  TPS53313 is a nice chip to supply negative power from +5V,  also because The maximum Vin can reach

20V, it will be  more reliable than a lot of chips which  maximum Vin is just 5.5V.

Hongxing Zhu

Beijing Infotronix Co. Ltd.

Good to know!

Just be careful when you do the -1.8, your duty cycle and OC will change compare with regular design.

regards

Mingyue

Thanks very much, I will take care of it.

Best regards!

Hongxing

Beijing Infotronix