TPS61178: Boost converter from 2.7V-3.6V to 15V with a TPS611781 boost converter

D3jun58

Part Number: TPS61178

Hello,

I would like to make a boost converter from 2.7V-3.6V to 15V at a maximum output current 1A (just every 1 second for 40 ms) and an average output current lower than 100 mA.
I choose TPS611781RNWR step up converter for this job. I used WEBENCH which gave me next schematic:

I made a switcher with values of components, but switcher doesn't work.
Measured voltages on pins are next:
BST: 4.68V
VIN: 3.58V
EN: 3.3V
VCC: 5.1V
DISDRV: 0.17V
FB: 0.43V
COMP: 1.19V
ILIM: 1.2V
FREQ/SYNC: 0V

For a M3 transistor I used STT4P3LLH6 from ST Microelectronics and for inductor I used XAL7030-152MEC made by Coilcraft.

Firstly, I noticed that WEBENCH gave me 931k and 86k6 resistors for a feedback, but if I calculate output voltage with this two values of resistors by formula in datsheet I get a lower voltage (around 14.1V), but this must not be a reason for non-working.
What could be wrong in my example?

Many thanks!
BR,
Dejan.

over 5 years ago

0 Jasper Li over 5 years ago

TI__Mastermind 46905 points

Hi Dejan,

what is the output voltage at the circuit?

what is the output capacitor using? and please change the Rcomp to 15K and Ccomp=6.8n

0 Minqiu Xie over 5 years ago

TI__Mastermind 21565 points

Hi Dejan:

May you export the WeBench simulation into TINA model, and then upload in this forum to let me check?

Export TINA-TI Transient Spice Model from WEBENCH :http://www.ti.com/lit/mo/slvmay6a/slvmay6a.pdf

I did the simulation with XAL7030-152MEC and Si7633DP as M3, it works well.

0 D3jun58 over 5 years ago in reply to Jasper Li

Intellectual 370 points

Hello Jasper,

Cout consists of parallel combination of 3 x 22 uF / 25V (C3216X5R1E226M160AB) capacitors. Voltage on them is exactly 5V.
Cout1 constits of parallel combination of 2 x 10 uF / 25V (GRM21BR61E106MA73L) capacitors.

I will change Rcomp and Ccomp...I will let you know...

Thanks!
Best regards,
Dejan.

0 D3jun58 over 5 years ago in reply to Minqiu Xie

Intellectual 370 points

Hello Miniqiu,

TINA model is attached to this post.

Many thanks,
Best regards,
Dejan.WBDesign120_TINA-TI.zip

0 Minqiu Xie over 5 years ago in reply to D3jun58

TI__Mastermind 21565 points

Hi Dejan:

I guess the phenomenon you observing is the soft start phase.

I have checked the simulation model. It could work well in TINA, with setting simulation time longer than 8ms to ensure it complete the soft start. It will take some time, just wait with patience.

0 D3jun58 over 5 years ago in reply to Minqiu Xie

Intellectual 370 points

Hello Minqiu,

switcher doesn't work also if I keep it enabled for a few minutes. I get only 5-5.1V on output.
I must say that I can hear some audiable noise from inductor and also I think that inductor became a little warm also when is no load on output. If I connect load on output, output voltage drops.
Maybe important information is that Cin (input capacitor) constists of 3 x 22 uF / 16V (1206X226K160CT) capacitors.

Many thanks,
Best regards,
Dejan.

0 Minqiu Xie over 5 years ago in reply to D3jun58

TI__Mastermind 21565 points

Hi Dejan:

So there is no load during the startup, right?

Please catch the waveform during the startup. Especially for Vin, SW and Vout pin, together with the voltage after the external FET. Thank you.

0 Minqiu Xie over 5 years ago in reply to Minqiu Xie

TI__Mastermind 21565 points

Hi Dejan:

As long time not hear you, I assume you have solved the issue. I'll close this post.

If not, just reply below. Thank you~

0 D3jun58 over 5 years ago in reply to Minqiu Xie

Intellectual 370 points

Hello Miniqu,

sorry I was out of the office in previous two weeks...
I re-soldered all components and now switcher works!! But output voltage is around 14.2 V and not 15 V as choose in simulation tool. But for values of 931kOhm (Rftbt) and 86k6 (Rfbb) 14.2V is correct value. I think that there is drift in Webench?

The switcher now works but I can measure very high current consumption when there is no load on output. Around 40-50mA ... and when I touch components around COMP circuit with finger, electrical consumption drops...maybe the values for COMP circuit are not right calculated by Webench?

Many thanks,
BR,
Dejan.

0 Minqiu Xie over 5 years ago in reply to D3jun58

TI__Mastermind 21565 points

Hi Dejan:

So glad to hear it works now.

According to the calculation, the Vout is around 14.1V. The Webench may don't have enough resistance value for divide.

For the power consumption, it's mainly caused by the FPWM mode for TPS611781. May I know why you select TPS611781? If you care lot about the efficiency with light load, I'll recommend the TPS61178 for you. TPS61178 has power save mode and consume much less power during the light load.

Power management

Power management forum

TPS61178: Boost converter from 2.7V-3.6V to 15V with a TPS611781 boost converter