Questions Regarding TPS61170 Application Report SLVA319C

Kenichiro Kurihara

Other Parts Discussed in Thread: TPS61170

Hi,

I have several questions regarding the SLVA319C report.

I have simulated Gt(s) equation (7) on page 7 and did not get the same plot as Figure 2. I added an additional pole modeled by a stray capacitance of 10pF and arrived at the same plot. Is that what TI did here?

I used the equation (8) as well as (9) and modeled GPW(s) and did not get the same plot as Figure 3. When I added a factor of 100 to SE equation (11) I arrived at the same plot. Is there a factor of 100 missing in SE? What are the A and F values used for the plot in equation (11)? I used A = 12290 equation (11) of the TPS61170 datasheet and F = 1Mhz for my simulation. 100 also is the DC gain for GPW(s).

Finally I'm hoping to use the IC to go from 14V to 24V @ 150mA. Following the application report I arrived at a inductance of 63uH. Is that too large. The datasheet recommends 10uH~22uH.

Thanks,

Ken

over 11 years ago

0 Jim Chen (SEM) over 11 years ago

TI__Intellectual 2370 points

I think you can start with 10uH as Fig.9 says on D/S pg.19.

0 Kenichiro Kurihara over 11 years ago in reply to Jim Chen (SEM)

Prodigy 20 points

Jim,

Because my required current is low, with a 10uH inductor my Ip will be larger than Kind * Iin_DC. The application note SLVA319C suggest not to do. Can you comment on that?

Also I'd really like to get answers on the initial questions I asked about what Se values were used for the simulation in the application note.

Ken

0 Jim Chen (SEM) over 11 years ago in reply to Kenichiro Kurihara

TI__Intellectual 2370 points

Pg.1 of SLVA319C is a reference design for 24V output. Iout can goes up to 300mA.

So you are OK with 22uH. 10uH should also be Ok according to Figure19 on datasheet.

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Questions Regarding TPS61170 Application Report SLVA319C