TPS61170 in SEPIC

uMin

Intellectual 860 points

Other Parts Discussed in Thread: TPS61170, TPS61170EVM-316, TPS55340, TPS61175, TPS61500

Hi,

Would like to use TPS61170 in SEPIC mode. However it seems like both SwitchPro and Webench are unable to do simulation in SEPIC config. Is there any tools that can do SEPIC simulation with TPS61170 ?
Can the SW pin used as an MOSFET driver to drive a larger external FET ?

Thanks for your help.

Regards,

CM.

over 13 years ago

0 Jeff F over 13 years ago

TI__Guru**** 166416 points

Regarding 1, unfortunately SEPIC designs are not scheduled to be included in WeBench for a few more months. However, there are app notes (http://www.ti.com/litv/pdf/slva337 and http://www.ti.com/litv/pdf/slyt309) and a TPS61170EVM-316 SEPIC EVM that might help.

Regarding 2, no. However, you might consider the TPS61175 or TPS55340 if you need more power. There are SEPIC EVMs for both of those.

0 uMin over 13 years ago in reply to Jeff F

Intellectual 860 points

Hi Jeff,

Thanks for your prompt response. I would like to use a PWM signal into the CTRL pin of TPS61170 to adjust the output voltage depending on load condition. Is there any higher power part with this CTRL pin ?

Thanks,

CM.

0 Jeff F over 13 years ago in reply to uMin

TI__Guru**** 166416 points

The TPS61500 is the LED driver version of the TPS61175. You can use it configured for analog dimming like d/s Figure 1 and with the OVP circuit set slightly higher than your highest output voltage. Then use a PWM signal on the EN pin to change the voltage on FB pin.

0 uMin over 13 years ago in reply to Jeff F

Intellectual 860 points

Hi Jeff,

Thanks for your quick response.

Can TPS61500 be configured in SEPIC ?

Thanks,

0 uMin over 13 years ago in reply to uMin

Intellectual 860 points

Hi Jeff,

I just found your comment in the following message, so I guess the answer to my previous question is Yes.

http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/68973/249642.aspx#249642

Thanks for your help,

CM.

0 Jeff F over 13 years ago in reply to uMin

TI__Guru**** 166416 points

Yes, the TPS61500 can be configured as a SEPIC. You would design it the same as TPS61175, replacing the LEDs with a resistor.

0 uMin over 13 years ago in reply to Jeff F

Intellectual 860 points

Hi Jeff,

In TPS61500 analog dimming config, what is the max PWM freq that can be applied to the EN pin ? In the datasheet, it spec PWM freq range as 200Hz to 1000Hz. On the EVM, 40kHz PWM signal is used, and it still works well. Is it safe to use higher freq than those spec in the datasheet ? We try to avoid switching in the audible range.

Thanks.

CM.

0 Jeff F over 13 years ago in reply to uMin

TI__Guru**** 166416 points

We haven't tested the IC for switching frequencies that high so we cannot guarantee operation (specifically accuracy) at frequencies above 1000 Hz. The IC works by using the input PWM signal to drive a chopper circuit to reduce the bandgap voltage and therefore change the LED current. With the capacitor on DIMC, the ripple on VREF and therefore FB is minimal. The audible noise problem is caused by ripple on ceramic output capacitors. You should not have audible noise even at the lower frequencies.

0 uMin over 13 years ago in reply to Jeff F

Intellectual 860 points

Hi Jeff,

Thanks for your reply. If you look at Figure 11 in TPS61500 datasheet, it seems to indicate that Analog Dimming Linear can be acheived with PWM freq at 200Hz, 5kHz and 40kHz. And looks like it is able to operate at least up to 40kHz. But under the section "Recomended Operating Conditions", it says PWM dimming freq range is 200Hz - 1000Hz.

Thanks,

CM.

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TPS61170 in SEPIC