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TPS54620: Vsense lead length

January 27, 2019, 4:53 pm
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Part Number:TPS54620

We have a design where it's better for us to put the TPS54620 on a daughter board, where the load (FPGA) is on the mother board. One approach is to use a bunch of pins on the connector between the boards to mitigate voltage drops. The other approach is to run the Vsense lead down the connector to the FPGA and use fewer pins on the connector. One engineer doesn't think that will work. How long can we run the pins between the Vsense pin to the load? Are there any considerations for the compensation network from the load to the Vsense pin?

Thanks.

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TPS65217: connecting VDC3 to VLDO1 after programming it for 3.3V operation

January 27, 2019, 5:24 pm
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Part Number:TPS65217

Hi,

We have a prototype design using the TPS65217C PMIC powering a Compute Module (raspberry pi) and associated peripherals (like LAN9514 and wifi chip).

We also use an STM32L4 to provide additional features that is powered from VLDO1, and this STM32L4 micro programs the voltages on the PMIC and starts it up (via PWR_EN pin). The VLDO1 is reprogrammed to output 3.3V so the STM32L4 can function at 3.3V as it is connected to 3.3V chips. This works great.

However we now would like to replace the STM32L4 with a higher powered STM32H7 micro, and I am worried that it will consume more current than VLDO4 can provide (100mA). However I cannot simply connect the STM32H7 to a VDCx pin (as they provide 1.1A each) as they don't turn on at startup, only VLDO1 provides voltage on startup, and we require the STM32H7 to program the PMIC and turn the other outputs on.

So I was wondering if we could connect VDC3 directly to the VDD rail that powers the STM32H7, this will be powered from VLDO1 at startup, the STM32H7 at reset draws approx 10mA until it speeds up and peripherals are enabled. Then once the PMIC is programmed and turned on, VDC3 outputs 3.3V to the STM32H7, and I assume there is no consequence to VLDO1 as it is a voltage regulator, and having 3.3V on its output will turn it off since it is higher than 1.8V.

Is my logic correct? Is there a better way to do this? Do I need to isolate VLDO1 from higher voltages? Do I program VLDO1 to 3.3v so its the same level as VDC3 at 3.3v? Do I insert a load switch that isolates VLDO1 after startup (then I have the problem of finding a load switch that prevents reverse current)?

Thanks in advance,

Kyran McGlasson
SAGE Automation

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Question of TPS54325

January 27, 2019, 5:30 pm
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We have a question.

Please tell us the current to set EN=High.

In datasheet, the voltage of EN pin is 1.6V to set EN=High.

Does this IC have the condition about current of EN pin?

Best regards,

Takahiro Nishizawa

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BQ27542-G1: How to fix the SOC

January 27, 2019, 5:32 pm
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Part Number:BQ27542-G1

Hi,Sir:

     For the test purpose, we want to fix the SOC value,

How to fix it?

Thanks!

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LM74700-Q1: LM74700-Q1 N-MOS Drive Question

January 27, 2019, 5:59 pm
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Part Number:LM74700-Q1

Hi Team,

My customer is trying to use the LM74700-Q1 for an ORING design. 

The part of it can be seen as below:

However, when the circuit started working, we captured the voltage drop on C16, which means the Vanode-Vcap, as beblow.

As you can see the charge pump seems working well at the very beginning, which raise to ~13V, then drop to ~12V, then raise to ~13V..etc. After ~100ms, it dropped to 5~6V as below, which lead to the failure of this design. 

Could someone help to comment on why this voltage dropped? Any issue with the current design? 

I would appreciate any comment! Many thanks!

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LM3464A: About the LED drive power supply

January 27, 2019, 6:03 pm
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Part Number:LM3464A

Dear all:

       Please find an existing LED drive power supply project:

Input characteristics: 1. Input voltage: 120v-277vac frequency: 47-63hz; 2.2. Harmonic (THD):THD 15% (120-277vac);3. The PF: 0.95 PF or less (120-277 - vac)

Output characteristics: 1. Two groups of outputs, the output power of each group is about 15W Pout=15W, the total output power is P =2Pout=15*2=30W;2. During normal operation, the lamp voltage is Vout= 42-43v, and each group has independent open circuit and short circuit protection functions;3. The output is constant current, and the output current of each group is Iout= 340-360ma, and the center value is Iout=350mA;4. Dimming: 0-10v dimming. When the DC Source is adjusted to "0v", the light shall be turned off, and the light shall not flicker;5. Efficiency: over 90% output efficiency of the whole machine (120-277vac)

Q1:Can this scheme be realized with LM3464A?LM3464A can support 0-10v dimming. Should the light be turned off when the DC Source is adjusted to "0v" and there should be no flicker?

Q2:Is there a cheaper, more appropriate device proposal?

  • Please find an existing LED drive power supply project

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Variable high voltage/high current DC buck converter

January 27, 2019, 6:14 pm
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Hi,

I have a need to design a buck converter that can step down from 400 Vdc to variable output from 40 to 300 Vdc. The source supply is 1KW, so the current can be up to 2.5 A. The control voltage is preferably a serial digital, but a variable dc input from 0-5 Vdc will work. Is there a reference design with TI chip that I can learn from? Thank you,

Bobby. 

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LM5145EVM-HD-20A: high current consumption at 0A loading

January 27, 2019, 6:35 pm
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Part Number:LM5145EVM-HD-20A

Hi expert,

My customer used LM5145 at their industrial design. They used two LM5145 EVMs to achieve two phase Buck topology. But when they tested with single EVM board, they found out Iin is high about 35mA when Vin=30V and Iout=0A. I also tested another EVM board and the result is the same. Would you kindly help to check if it is normal operation? Thanks a lot!!

Best regards,

Ann Lien

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UCC2895: VCC is shorted to GND

January 27, 2019, 7:01 pm
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Part Number:UCC2895

when debugging the PSFB circuit with UCC2895,  it is founded that VCC pin is shorted to PGND pin.

could you advise possible reasons can result the phenomenon? TKS.

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BQ25898: BQ25898 thermal question

January 27, 2019, 7:07 pm
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Part Number:BQ25898

Hi,

Customer did the thermal measurement with BQ25898.

We found the max temperature of the chip is 91 degree C during 3A charging.

The spec. of max operation temperature is 85 degree C.

The measurement is based on without shielding case(open frame).

Could you check if this number is reasonable?

Best regards,

Randy Chen

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TPS54340: TIDA-IPAD-AUTOMOTIVE-CHARGER-REFERENCE-DESIGN

January 27, 2019, 7:41 pm
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Part Number:TPS54340

Dear Sir,

My customer would refer this reference design, he would know D100 function ?

Thanks!

Steven

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TPS7A63-Q1: TPS7A63-Q1 ESD Sensitive & pcb Layout problem

January 27, 2019, 7:57 pm
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Part Number:TPS7A63-Q1

Dear TI:

   Custom use tps7a6350-q1 for ESD Test, But it fauiled ----nReset pin output low voltage.and external light blink one time.
the output cap is 10uf*3=30uf.  I Double may the bad PCB layout cause the problem.

the test condition: 
ESD Voltage : 2kv /4kv ...
 

I Double the interruption from the nReset net.  Cause the 5v  output voltage (white led) has no blink.


Pcb Layout as fellow:

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TPS22916: Auick discharge of TPS22916

January 27, 2019, 8:21 pm
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Part Number:TPS22916

Hi

Please let me ask you a question about TPS22916 just in case.
I think this device has quick output discharge.
Does this function operate under disabled and no input?

Best regards,
Yokota
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UCC256302: UCC256302 VCR capacitance is set, the calculated value and the theoretical value are deviated

January 27, 2019, 8:44 pm
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Part Number:UCC256302

Problem: When the VCR is set, the calculated value and the theoretical value are deviated. VCR is divided into capacitance, according to calculation, cl2 47pF, cl9 10nF
 
This set of parameters with full load limit power, VCR will be clamped to 7V
 
Adjust cl9 to 6.8nF, it can be loaded normally, VCR is 5.6V
 
Attach a calculation book and related schematics to help you see where the problem is?

By the way, look at other parameters are there any problems?
 

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TPS8268090: TPS8268090 Inductor Body and Substrate clearance

January 27, 2019, 8:59 pm
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Part Number:TPS8268090

Hi TI Experts,

We need to know what is the gap ( minimum height ) under the inductor component between inductor body and substrate, please refer picture below :

The concern is we need to use mold compound with correct filler size to prevent any unfilled/void.

Please advice,

Thanks,

Teach Me

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UC3843: DC/DC 12Vdc to 280Vdc 400W

January 27, 2019, 9:14 pm
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Part Number:UC3843

Hi Sir,

We are designing DC/DC power supply.  Spec requirement as below. 

Input : 12Vdc

Output : 250Vdc -280Vdc  , 400W

1) Could you please recommend suitable IC or reference design ? 

2) Can we use p/n UC3843 ?  Or Does it have other more suitable IC ? Please help to recommend. 

BR,

CCphi

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TPS92661-Q1: For unused LED pins

January 27, 2019, 9:22 pm
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Part Number:TPS92661-Q1

Hi team,

Can you please reply the following quetion?

In TPS92661-Q1, the datasheet recommends "When configuring for connections having fewer than 12 LEDs, the LEDs should be connected as shown in Figure 34."

-. What is the purpose of connecting the unused pins to GND? Is it just for reducing power consumption, otherwise for making current path to GND?

-. If the unused pins are not connected to GND, what is the expected problem?

Thanks,

Sam Lee

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UCC5310: UCC5310M

January 27, 2019, 9:41 pm
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Part Number:UCC5310

Hi,

In our design we are using UCC5310MCDR gate driver IC but this is non-Automotive part.

Please recommend the Automotive  alternate part for the same.

Specifications:

Temp: -40 to 125 degreeC/150 degreeC

Qualification: AEC/RoHS

Status: Active

 

 Thanks,

Priyanka

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TPS22965: Non functioning of TPS22965NQWDSGRQ1 load switch

January 27, 2019, 9:55 pm
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Part Number:TPS22965

We are using two load switches TPS22965NQWDSGRQ1(U202) and TPS22965QWDSGRQ1 (U203) in our design.

Please refer the attached images (Sch1 and Sch2) for design reference.

Design Details : 

ParametersU202U203
Input Voltage3.3V1.8V
Bias Voltage5V5V
Enable signal Controlled by uC (3.3V LVCMOS level)Controlled by uC (3.3V LVCMOS level)
CT voltage (probed after fault)0V0V
Output Voltage (probed after fault)0V0V

Problem observed :

Load switch outputs are not raised as we expected even though the input voltage, Enable signals are driven properly.

Things noted:

CT voltage is not appeared on the CT capacitor pin.

Suspected that load switch is not able to generate the gate voltage, hence output voltage is not appeared at the output.

Clarification / Support required:

Causes which will failure the load switch.

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BQ78350-R1: the LEDs display wrong at low temperature

January 27, 2019, 10:07 pm
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Part Number:BQ78350-R1

Hello:

         First fully charge the batteryunder and at low temperature （-30℃），the battery can discharge more than 2 hours!

Fully charge the battery ,then discharge the battery at -30℃. After a few minuters and press the LED button，only the LED1 blink .LED2...LED5  not bright.

Actually there's a lot of remaining capacity, I use five LEDs to display the capacity，So under low temperature the display of remaining capacity is inaccurate.

I want to know what am I setting up wrong?(Please visit the site to view this file)

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