TPS40170: TPS40170 OUTPUT SHORT ISSUE

ANBARASU SEMBANAN

Prodigy 140 points

Part Number: TPS40170

Hi All,

I am using the TPS40170RGYT for the below configuration,

Input :45 -50 VDC

Typical: 47.5VDC

Maximum Output Current: 8A

Output Voltage: 35VDC

Switching Freq: 197.239 kHz

While performing the fist power ON itself the output voltage observed as 0.3VDC instead of 35VDC . Further subsequent verification the IC getting abnormal heat & observed at the SW pin w.r.t GND impedance was 5.7 Ohms.

Removed the IC & verified the impedances for the below points w.r.t GND,

LDRV-202.8 Ohms

VBP-14.3 Ohms

SW-5.7 Ohms

HDRV - 72.6 Ohms

BOOT - 4.9 Ohms

Please suggest the what is the impact to make the output to get short with ground & attached the schematic for reference.

Looking for the valuable feedback.

Note: I checked in web bench design & I am able o get the output voltage as I am expected.

Regards,

S.Anbarasu.

over 7 years ago

0 ANBARASU SEMBANAN over 7 years ago

Prodigy 140 points

WebenchReportsServlet3.pdf 8688.SCH.docx

0 Ambreesh Tripathi over 7 years ago in reply to ANBARASU SEMBANAN

TI__Expert 6860 points

Anbarasu ,

Here are the recommendations on debugging the issue :

1. Since you have changed the output capacitance for your design . You will need to re compensate to ensure closed loop stability . Here is the design with 470uF output capacitance .

webench_design_1225793_857_690014180.pdf

2. During the power turn on event , Please probe the input voltage , HDRV , LDRV and Switch node and share the result .

3. How is the Switch node waveform looks like ? Does it have lot of ringing ?

4. Please share the Layout for the review .

---Ambreesh

0 ANBARASU SEMBANAN over 7 years ago in reply to Ambreesh Tripathi

Prodigy 140 points

Hi Ambreesh,

Thanks for your feedback!

I removed the fault TPS40170 IC and replaced with new one & measured the below output voltages for the input,

S.No	Input Voltage	Output Voltage	Supply Current
1	5V	3.761V	0.003A
2	10V	3.98V	0.004A
3	15V	4.145V	0.004A
4	20V	4.308V	0,004A
5	25V	4.458V	0.004A
6	30V	5.475V	0.005A
7	35V	6.54V	0.005A
8	40V	7.25V	0.005A
9	45V	7.83V	0.005A

2) Attached the waveforms as requested.

3) Yes I am observing the ringing at SW pin.

4) Attached the PCB file for your review.

a) HDRV Waveform

a) LDRV Waveform

c) SW_BEFORE INDUCTOR

d) SW_BEFORE INDUCTOR STABLE OP

e) SW_AFTER INDUCTOR WAVEFORMBRD01002_REV_B1.pcb

0 Ambreesh Tripathi over 7 years ago in reply to ANBARASU SEMBANAN

TI__Expert 6860 points

Anbarasu ,

THe PCB file is not attached with the reply . Can you please repost witht he PCB file .

Also did you try recompensating the design ? Also the the Mosfet gate Drives are low then how come you are getting high voltage at the SW node ?

---Ambreesh

0 ANBARASU SEMBANAN over 7 years ago in reply to Ambreesh Tripathi

Prodigy 140 points

Due to the AGND & PGND shorting was missed in the PCB design ,so due to that the output voltage measured high.
I did manual short & verified on the next module and working fine .

Power management

Power management forum

TPS40170: TPS40170 OUTPUT SHORT ISSUE