TPS62742: Technical Inquiry at 400mA

TI-CSC

Genius 12995 points

Part Number: TPS62742

Hello E2E Experts,

Good day.

We want to make a final decision on a DCDC in the next couple of days, I wonder if we could get some help.

Requirements

Vin = Li-po battery (3.2~4.2V)

Vout = 3.3V (if Vin is less than 3.3V, it's ok to

Iout = typically 150uA, peak 350mA during RF activity.

Design goal: >90% efficiency across the full range

TPS62742

https://www.ti.com/product/TPS62742

This is the ideal candidate, but the datasheet says the output is limited max when the Vin is less than 0.7V higher than Vout. We want to clarify why it cannot delivery 400mA.

Thank you in advance for your assistance.

Regards,

CSC

over 2 years ago

0 Moheddin Pasha Shaik over 2 years ago

TI__Mastermind 18410 points

Hello Given,

Thank you for reaching out.

0.7 V would be the voltage drop due to the high side FET and the inductor. If you operate the device beyond that condition it could enter into 100% Duty cycle mode.

Thank You,

BR,

Moheddin

0 TI-CSC over 2 years ago in reply to Moheddin Pasha Shaik

TI__Genius 12995 points

Hello Moheddin,

Good day.

Just one follow-up, for TPS62742, what will happen if we run the 300mA for 100mS pulses at a 1sec period when it’s in 100% duty cycle mode?

Regards,

CSC

0 Moheddin Pasha Shaik over 2 years ago in reply to TI-CSC

TI__Mastermind 18410 points

Hello CSC,

Can you please provide me your test conditions such as Vin, Vout and Iout. Because the device enters into 100% duty cycle mode based upon the your Vin, Vout and Iout.

TI-CSC said:
what will happen if we run the 300mA for 100mS pulses at a 1sec period when it’s in 100% duty cycle mode?

Lets imagine that the device is in 100% duty cycle mode, then the high side FET is always ON and the Vout follows the Vin with reduction in voltage drop due to Rds ON of high side FET and inductor DCR. Now if there is a load transient condition, the device jumps form 100% duty cycle mode to switching mode based upon the load transient current.

TI-CSC said:
if we run the 300mA for 100mS pulses at a 1sec period

Can you please elaborate the condition.

Thank you,

Regards,

Moheddin.

0 TI-CSC over 2 years ago in reply to Moheddin Pasha Shaik

TI__Genius 12995 points

Hello Moheddin,

Good day.

Our test condition:
Vin = 3.3
Vout = 3.0
Iout is dynamic based on the wireless SoC.

Pls, see attached. This is a typical current consumption profile on 3.3V rail during 10 second period consumed by the TI CC3235 module we have.

Attachments.zip

You can see there are periodic WiFi activities that peak up to more than 150mA, but most of the time is much less than 100mA. It can be as high as 300mA for 100mS for each 1-second period.

What is the risk of using TPS62742?

Regards,

CSC

0 Moheddin Pasha Shaik over 2 years ago in reply to TI-CSC

TI__Mastermind 18410 points

Hello CSC,

I will get back to you by end of the day.

Thank you,

Regards,

Moheddin.

0 Moheddin Pasha Shaik over 2 years ago in reply to Moheddin Pasha Shaik

TI__Mastermind 18410 points

Hello CSC,

The 400mA maximum current defined in the datasheet is the sum of ILOAD and IOUT. So the maximum IOUT for TPS62742 is 300mA.

I assume you are using only the IOUT for output. In this case your load is exceeding the maximum load conditions.

I see the maximum load of 413.21mA in the attachment you shared. If your load is around 300mA with transient then you can go with TPS62742.

I would recommend our new device TPS628438 which is having smaller Iq of 275nA and also 600mA load capability available in WCSP package. (TPS62843 data sheet, product information and support | TI.com)

You can also check our lowest Iq device TPS6284X- (TPS62840 data sheet, product information and support | TI.com)

If you have any further questions please feel free to contact.

Thank you,

Regards,

Moheddin.

0 Moheddin Pasha Shaik over 2 years ago in reply to Moheddin Pasha Shaik

TI__Mastermind 18410 points

Hello CSC,

If you don't have any further questions, can you please close the thread by clicking on Resolved.
Thank you,

Regards,

Moheddin.

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TPS62742: Technical Inquiry at 400mA