TPS61178: Optinal parameter for COMP pin

Hirokazu Takahashi

Part Number: TPS61178

Hello Support team,

Could you support below question?

Q1. Could you let me know the maximum value of STARTUP?
Q2. We want to keep the output voltage drop due to load transient under 0.45V under the following conditions. May I request ot estimate the optimal constant of COMP terminal?
* Vin : 4.5V~9.5V
* Vout : 12V
* Iout : 1A
* Fsw=1MHz
* L=1.5uH(DFE322520F)
* Cout=6.5uF(min)~9.9uF(max) or 11.5uF(min)～17.4uF(max)
with Ceramic capacitor

Best Regards,
Hirokazu Takahashi

over 6 years ago

0 Jasper Li over 6 years ago

TI__Mastermind 46905 points

Hi Takahashi-san

what is the meaning of " maximum value of STARTUP?"? is it the maximum startup time.

the COUT is the effective capacitance considering the DC bias, correct?

0 Hirokazu Takahashi over 6 years ago in reply to Jasper Li

TI__Expert 8420 points

Hello Jasper-san

Thanks for your reaching out.
Sorry for my typo.

"maximum value of STARTUP" means "tSTARTUP, Startup time".
Cout means output capacitor.

Best Regards,
Hirokazu Takahashi

0 Jasper Li over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 46905 points

Hi Takahashi-san,

it is for the same application that you also request efficiency, correct?

if yes, let's finalize the power components firstly.

0 Hirokazu Takahashi over 6 years ago in reply to Jasper Li

TI__Expert 8420 points

Hello Jasper-san

Thanks for your suggestion.
Yes, but Q1 is inquiry regarding specification. May I ask it on this sread?
Q1. Could you let me know the maximum value of tSTARTUP?

Best Regards,
Hiroakzu Takahashi

0 Jasper Li over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 46905 points

Hi Takahashi-san,

For tps611781

it is approximately 76mA at 4.5V input and 23mA at 9.5V input from the EVM

the startup time is also related to the VIN. refer to the page 3 of this application note to calculate the startup time

http://www.ti.com/lit/an/slva940a/slva940a.pdf

0 Hirokazu Takahashi over 6 years ago in reply to Jasper Li

TI__Expert 8420 points

Hello Jasper-san

Thanks for supporting the current data at no load condition.

I have question regarding tSTARTUP.
According to "8.3.3 Startup" in p.11 datasheet, I think that tSTARTUP
will mean soft start time.
It may relate with VREF and VFBSS according to the equation (2) at p.3 in the application note which you attached in previous post. What is VFBSS?

Best Regards,
Hirokazu Takahashi

0 Jasper Li over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 46905 points

Hi Takahashi,

the startup of this device divide into precharge phase and linear ramping-up phase. the pre-charge phase is typical 2.6ms.

the linear ramping-up phase period is 3.2mS from if the FB voltage is from zero to 1.198V. but the FB is not from zero in real application. so this period can be calculated through equation (3) of the application note. VFBSS is ramping up rating of the FB pin voltage.

0 Hirokazu Takahashi over 6 years ago in reply to Jasper Li

TI__Expert 8420 points

Jasper-san

Thanks a lots.
Both of datasheet and application note describe tSTARTUP as typ 3.2ms.
I understand we can calculate the soft start phase time by equation(3) in application note.
But we want to know the maximum time of startup.
Could you let me know maximum value of tSTARTUP?

Best Regards,
Hirokazu Takahashi

0 Jasper Li over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 46905 points

Hi Takahashi,

there is no min/max for this spec. from process variation, I would expect +-20% variation.

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TPS61178: Optinal parameter for COMP pin