LM5175EVM: Getting Short after some time interval

gagandeep singh

Part Number: LM5175EVM
Other Parts Discussed in Thread: LM5175, LM5176, LM5175RHFEVM-HD

Hello

I am using LM5175 to generate 12 V and 6 A output .

The input voltage range is 20- 34 V which is obtaining through step down tansformer and Full wave Bridge Rectifier.. The Switching frequency is 120kHz .

Either HDRV1 and SW1 or HDRV2 and SW2 are getting short. Please suggest the solution for this . Please find the attached Schematic also

over 7 years ago

0 Vijay86929 over 7 years ago

TI__Genius 11490 points

Hi Gagandeep,

It is not clear why a buck-boost converter is needed in this application considerating that VIN is alway higher than VOUT.

0 gagandeep singh over 7 years ago in reply to Vijay86929

Intellectual 300 points

Hello Vijay

We have another usecase with DC supply for boost conversion. TI local FAE suggested to go with this part

0 Alan Martin over 7 years ago

TI__Expert 4365 points

What is the value of the bulk capacitor that follows the bridge rectifier previous to being attached at VCC_IN of the included schematic?

What is the amount of 100Hz or 120Hz voltage ripple present at VCC_IN?

0 gagandeep singh over 7 years ago in reply to Alan Martin

Intellectual 300 points

Hi Alan

Please Find the Schematic Before VCC_IN and Ripple waveform input to the VCC_IN.

We have attached 3 bulk caps of mili farad value before VCC_IN to filter the DC .

0 Priyanka Khangarot over 7 years ago in reply to gagandeep singh

Prodigy 150 points

Hi TI Team,

Please help on the above issue.

0 Vijay86929 over 7 years ago in reply to Priyanka Khangarot

TI__Genius 11490 points

Hi Gagandeep,

Not sure if I understand the meaning of HDRV1 - SW1 short. Can you elaborate a little what abnormal behavior you see?

We typically suggest using a 8.2V zener clamp across BOOT2-SW2 (across CBOOT2). Same suggestion for CBOOT1.

Regards

0 gagandeep singh over 7 years ago in reply to Vijay86929

Intellectual 300 points

Hi Vijay

Impedence across HDRV1 and SW1 pin is 100kohm without input power.

With input power of 24 v AC, 12 V output is generated and output voltage gets drop after some time duration and impedence across HDRV1 and SW1 pins is about 90 ohm .

i have test with zener diode of 8.2 V and output starts fluctuating . please check the connections of diode .

0 Vijay86929 over 7 years ago in reply to gagandeep singh

TI__Genius 11490 points

Hi Gagandeep,

The zener across CBOOT1 (C18) is correctly placed. There should be a similar on across CBOOT2.

The symbol though belongs to a schottky so please double check.

I also encourage you to check LM5176 which is the newer slightly higher voltage version of LM5175. It is pin compatible with LM5175 in TSSOP package.

Regards

0 Vijay86929 over 7 years ago in reply to gagandeep singh

TI__Genius 11490 points

Hi Gagandeep,

The zener across CBOOT1 (C18) is correctly placed. There should be a similar on across CBOOT2.

The symbol though belongs to a schottky so please double check.

I noticed that you are usings 100V FETs. LM5175 works best with FETs with lower QRR and switching noise. I suggest optimizing the FETs to be somewhat similar to LM5175RHFEVM-HD.

I also encourage you to check LM5176 which is the newer slightly higher voltage version of LM5175. It is pin compatible with LM5175 in TSSOP package.

Regards

0 gagandeep singh over 7 years ago in reply to Vijay86929

Intellectual 300 points

Hello Vijay

We tested by mounting Zener diode (BZT52H-C8V2) on both CBOOT1 and CBOOT2. Do we require current rated zener diode ?

Result : It generated 12 V only in no load condition only, as the load of 0.2 A applied its output goes below 10V.

we are using QFN package of LM1575 , LM5176 is available in only TSSOP package cannot go with that.

0 Vijay86929 over 7 years ago in reply to gagandeep singh

TI__Genius 11490 points

Hi Gagandeep,

What abou the FETs (see my comments above)?

Regards

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LM5175EVM: Getting Short after some time interval