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TPS65251: Output Voltage is not stable in board to board

October 31, 2019, 8:01 am
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Part Number: TPS65251

We had manufactured 10 Nos of boards with TPS65251. In them around 8 Nos of baords, the output voltage of TPS65251 is working good without any issues

See the attached schematics.

 

But in remaining two boards we are facing the issues as the output voltage is not as per the expected.  0.7 V instead of 3.3V ; 1.5v instead of 2.5V, 1.2v instead of 1.8V.  The output is continuously fluctuating.

For the reference please find the below graph,

For 2.5v supply rail,  we are observing 2.5v and dropping to 1v & again returning back to 2.5V. with time period of 33msec

For 1.8v supply rail,  we are observing 1.8v and dropping to 0.5v & again returning back to 1.8V. with time period of 33msec

For 3.3v supply rail,  we are observing 1.8v and dropping to 0.7v & again returning back to 1.8V. with time period of 33msec

Also we had ensured all the resistor values are fine and 8 Nos of boards are working,  but two boards alone not working remaining boards never faced the issues.

Please support us

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TPS25200: Output discharge function in usb input protect application

October 31, 2019, 8:28 am
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Part Number: TPS25200

Hi Team,

Customer use TPS25200 in the usb protect circuit. Their output get large caps, the input cap is smaller compared with output cap. When they move away the USB input power, does it possible for the output discharge circuit discharge the output cap to 0V very fast? 

If not, is there any method to let the output discharge circuit work when move away the USB input? Could you give some comments on this application? 

Best Reards,

Will

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Sourcing Information TPS63810

October 31, 2019, 8:58 am
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(Please visit the site to view this file)

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WEBENCH® Tools/LM3488Q-Q1: Startup limitation current with my DC supply

October 31, 2019, 9:04 am
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Part Number: LM3488Q-Q1

Tool/software: WEBENCH® Design Tools

Good morning,

I designed a SEPIC using LM3488Q,

the problem is that when i turn on my power supply the output voltage stays at 3V (instead of 10V),

the Power mosfet does not have enough Vgs and the amount of current in the inductor keeps growing.

The scheme is the following:

the only difference is the power mosfet that I am using: FDD120AN15A

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BQ28Z610: Learning Cycle Not Successful - Log Provided For Review

October 31, 2019, 9:16 am
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Part Number: BQ28Z610

(Please visit the site to view this file)Hi there,

I am still having issues with completing a successful learning cycle with the bq28z610 gas gauge; attached are the log and data memory parameter files for the most recent attempt where I reduced the discharge and charge currents in an attempt to prevent significant cell voltage imbalance.  I am using LiFePO4 Tenergy 34009-0 cells setup in a 2S configuration.

I had previously been told that my charging setup was incorrect.  I've been attempting the learning cycles using a power supply set to the desired final charge voltage (7.3V) with it current limited to the desired charging current.  This appeared to cause problems as the taper current was never achieved and charging current would sometimes go in and out.  I was under the impression that the bq28z610 would regulate the charge current itself.  Is this true?  And what would be the best method for charging the cells?

I also reviewed our data memory parameters and did not find anything that seemed troublesome, but could this also be looked over?  Any feedback would be appreciated.

Thanks,

Nick

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UCC3895: 3KW phase shift schematic confirm

October 31, 2019, 9:33 am
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Part Number: UCC3895

sir,

could you help confirm any problems with the schematic, or have any suggestions,thanks for your help.

my specification: input 480v VDC to 380v VBUS/3KW.

(Please visit the site to view this file)

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LM431: Vref regulation voltage 2.6V instead of 2.5V

October 31, 2019, 9:32 am
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Part Number: LM431

Hello, I am using the LM431BIM3 in the control loop of a flyback converter. However instead of having a Vref of 2.5V, i am measuring 2.6V instead which makes my output regulates at 12.6V instead of 12V.

R2=4.7k, R1=18k, R3=2.2k, R4=1k, Cz=22n.

The voltage across R3=7V

The voltage across R4=1.1V 

voltage across VAK of LM431=3.9V

Can someone help me understand why Vref=2.6V? and how to make it 2.5V? I guess Vref is current dependent..

Thanks

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TPS62821: Can I design with 250uF output capacitance?

October 31, 2019, 9:52 am
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Part Number: TPS62821

Hi,

I’m working on a core power supply for a small FPGA and I have a few questions about some parts.

The requirements are:

Vin: 2.8 – 4.5V

Vout: 1.1V +/- 2.5%

Iout: 1 – 2 A

I’m looking at the TPS62821 (1A) and the TPS62825 (2A). Using the FPGA vendors tools I’ve come up with a capacitance requirement of about 250uF, however both of those parts don’t recommend more than 47 – 100uF of output capacitance, or at least suggest that other values should be evaluated carefully. The FPGA vendors tools model the power supply as a voltage source in series with a resistor (1m ohm by default) and an inductor (20nH). They suggest that those values should be adjusted to match the power supply’s datasheet, but I’m not sure how to come up with the correct values. It is possible that with better values for those parameters the capacitance requirements would be reduced. Do you have any idea how to characterize those things?

Both parts also recommend a feed forward capacitor for larger output capacitances. Is it possible to adjust the value of that capacitor to achieve stability with a larger output capacitance? If so, how would I go about doing that?

Thank you,

Lauren

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TPS731: Acceptable to force OUT pin to 4.2V?

October 31, 2019, 11:29 am
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Part Number: TPS731

I'm analyzing a potential fault condition where a 4.2 V stiff supply gets applied to the OUT pin of TPS731. The regulation FB network will be set for around 3.7 V. IN is at 5V (USB).

Is this safe for the part?

Will there be appreciable leakage current from OUT to IN?

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TPS65263-1Q1: SYNC POLARITY

October 31, 2019, 11:43 am
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Part Number: TPS65263-1Q1

I have a 67 % DC square wave, 1 Mhz, wich i want this TPSxx to syncronize to. This is exactly the switch node voltage of another buck, cascaded on the out of CH1 of TPS65263-1Q1.

Datasheet explains that:

-the active sync edge for TPS is the falling one.

-CH1 is 180° w respect to other channels

-on page 22 the period  "....At the end of every clock cycle, the low-side MOSFET sourcing current is compared to the internally set low-side sourcing current limit. ...." enforces the idea that the transition to 'ON' state will take place at cycle start, thus at sync pulse falling edge..... 

BUT

-Figure 63 on page 36 shows real case scoped signals. Polarity of signals here seem counterdicting explainations; Anyway CH1 here transition high a little while after the sync falling edge. So, if confirmed, a little inverting buffer may do.

Question:

1) what am i missing? Is it that CH1 is 0°, and CH2 & CH3 are 180° rotated, instead? This would explain everything. 

2) Apart from the reasons, will CH1 always have it's rising edge within a reasonably little time from sync fall, for every TPS DUTY CYCLE? 

Thanks, Francesco

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BQ40Z50-R2: chemistry data files

October 31, 2019, 12:11 pm
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Part Number: BQ40Z50-R2

Will BQStudio export the chemistry data to a file (e.g. srec, binary, text) as opposed to directly programming the bq40z50 gauge?

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UCC28704: Design validation of a 5V/1A Universal AC/DC

October 31, 2019, 11:43 am
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Part Number: UCC28704

We're developing a Universal AC/DC 5V/1A using the UCC28704, that was based on the WeBench Design Tool. We houve some doubts about the circuit, since we're using the 7508110151 transformer from Wurth, but can't seem to find any reference from it on the WeBench, will our circuit function correctly using these components ?

We will also need to supply some non-isolated components, which will require approximately 3V3/20mA. Is it possible to use the auxiliary winding with a low quiescent LDO ? If so, whre is the best place to connect it ?

Best Regards, Drauzio.

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TPS61088: Vout max

October 31, 2019, 12:39 pm
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Part Number: TPS61088

My customer needs to run the output voltage as high as 13V.  Does that mean the TPS61088 cannot be used? Must they limit it to 12.6 V output? 

What things should they be careful with running the output voltage so high?

Thanks

Viktorija

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Isolated DCDC converter/Module

October 31, 2019, 12:42 pm
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Hello,

I need an isolated power solution that can take 5Vin, 5 or 3.3Vout, and 10mA out.

Would Flyback be the best solution here because of the need for isolation? Could you recommend best solution/direct me to the best family of devices?

Thanks,

Adam

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TPS7A92: Rtheta JB Question

October 31, 2019, 12:49 pm
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Part Number: TPS7A92

We've noticed that the Rtheta-JB is 29.1C/W for this device TPS7A9201DSK. Comparing to the TPS7A7100RGT which has an RthetaJB of 17.2C/W

Why are the JB thermal resistances so dramatically different given the Rtheta JC specs are about the same -  is this correct?  Are there two different constructions inside? 

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BQ77915: BQ77915 EVM - How to Reset Overcurrent Fault Without Load Removal

October 31, 2019, 12:59 pm
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Part Number: BQ77915

Hello,

I have been having issues with trying to reset an over current fault with the BQ77915. Is removing the load the only possible way to reset the fault? This is not possible for our use case, so Ideally there would be another way to reset the fault. Connecting the battery charger is also not always possible for the product that this chip is being used for.

I tried using the BQ7791504, since that was recommended in a similar forum post to this one. I replaced the IC that was on the EVM with the BQ7791504. This ended up causing the overcurrent protection feature to not work at all, and I was able to draw a significant amount of current from my battery. This is not ideal, along with having the temperature sensing features disabled for the BQ7791504.

If removing the load is the only way to reset this fault, is there a similar TI chip that does not have this "feature"?

Regards,

Alex Mazur

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BQ77915EVM-014: Battery Balancing Occuring Whenever Battery is Plugged In

October 31, 2019, 1:03 pm
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Part Number: BQ77915EVM-014

Hello,

I am having battery balancing trigger whenever I plug in my 7S battery pack into the BQ77915EVM. According to the datasheet, battery balancing only occurs when a power adapter is plugged in (i.e. battery pack is being charged). However, I see battery balancing happening whenever I plug in my battery pack. What is the cause of this?

Regards,

Alex Mazur

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BQ25120A: inductor alternative for bq25120

October 31, 2019, 1:40 pm
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Part Number: BQ25120A


I'm using BQ25120A with spec recommended 2.2uH inductor - GLFR1608T2R2M-LR.
It was chosen due to the smallest package size in recommended inductors list - 0603 - and sufficient current - 150mA.
It is nearing the EOL so needs a replacement. 
It looks that CBMF1608T2R2M by TAIYO YUDEN would fit the bill. Can you please confirm this choice or suggest the alternative.
Thanks
Igor
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LMZ22010: Can this part and the LMZ23610 be synched to an SSFM clock source?

October 31, 2019, 2:05 pm
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Part Number: LMZ22010

The requirement is that the part must be able to be synchronized to an external spread spectrum frequency modulated (SSFM) clock source that has it's clock frequency spread over a bandwidth that is +/- 10% of the set frequency.

Do these 2 devices have that capability?

Thanks,
Lauren

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TPS65131: BSW Pin during fault conditions

October 31, 2019, 2:24 pm
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Part Number: TPS65131

Hello,

The device datasheet states that the device has both an internal current limit over voltage protection and a thermal shutdown protection. What the datasheet does not explicitly say is what happens to the BSW pin during a fault. If a fault occurs will the BSW pin turn off the PFET?

Thanks,

John

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