LM2623: About output rising time

Tsukui Yusuke

Guru 21930 points

Part Number: LM2623
Other Parts Discussed in Thread: TPS61240

Hi,

Customer is planning to use LM2623 following conditions.

[Conditions]

-Vin=3V to 4V

-Vout=5V

-Iout=250mA

-Out put cap=470uF

Customer wants to know how to calculate the rise time of this condition.
Alternatively,Is there a startup waveform for reference?

I confirmed it, but the information was not mentioned in the data sheet.
Could you give me your advice?

Best Regards,
Yusuke Tsukui

over 7 years ago

0 Jasper Li over 7 years ago

TI__Mastermind 46905 points

you can consider the TPS61240 for this application, the solution will be much smaller.

0 Tsukui Yusuke over 7 years ago in reply to Jasper Li

Guru 21930 points

Li-san,

Thank you for your support.
I will introduce TPS61240 to the customer.
However,Examination of the LM2623 had progressed in the customer.
Could you give me advice about LM2623 output rising time?

Best Regards,
Yusuke Tsukui

0 Tsukui Yusuke over 7 years ago in reply to Tsukui Yusuke

Guru 21930 points

Hi,

Can I get the information?
I will attach the waveform.
If you need more information or if I should clarify my comment ,
please let me know.

Best Regards,
Yusuke/Japan Disty

0 Garrett Roecker over 7 years ago in reply to Tsukui Yusuke

TI__Mastermind 21720 points

Hi Yusuke,

I'm looking into the question currently. Just to clarify the customer is looking for the rise time of the output voltage at start-up, correct? I will measure it on the EVM for the LM2623 and confirm.

Thanks,

Garrett

0 Tsukui Yusuke over 7 years ago in reply to Garrett Roecker

Guru 21930 points

Garrett-san,

Thank you for your response.
Customers will continue to want to know rise time.
Could you tell me your measurement data?

Best Regards,
Yusuke/Japan Disty

0 Garrett Roecker over 7 years ago in reply to Tsukui Yusuke

TI__Mastermind 21720 points

Hi Yusuke,

Measuring on the EVM the ramp up time is about 200us after the minimum start-up voltage is achieved on the input voltage.

Thanks,

Garrett

0 Tsukui Yusuke over 7 years ago in reply to Garrett Roecker

Guru 21930 points

Garrett-san,

Thank you for your kind support.
By the way,
Is there a way to calculate the rise time?

Best Regards,
Yusuke Tsukui

0 Garrett Roecker over 7 years ago in reply to Tsukui Yusuke

TI__Mastermind 21720 points

Hi Yusuke,

There is not an easy way to calculate the rise time. If the customer is wanting to extend the rise time of the output a diode, capacitor and resistor can be add as shown in figure 1 of this application report. By adding this circuit the rise time of the output will be increased.

Thanks,

Garrett

0 Tsukui Yusuke over 7 years ago in reply to Garrett Roecker

Guru 21930 points

Garrett-san,

Thank you for your kind correspondence.
I have read the application report.
I will introduce it to customers.

Best Regards,
Yusuke Tsukui

0 Tsukui Yusuke over 7 years ago in reply to Tsukui Yusuke

Guru 21930 points

Garrett-san,

Let me ask you one more thing.
Customer want to know the rise time when EN is set to High after voltage is applied to Vin.
(1.Vin start up　 2. EN→High)
Could you tell me the rise time and waveform?

Best Regards,
Yusuke Tsukui

0 Tsukui Yusuke over 7 years ago in reply to Tsukui Yusuke

Guru 21930 points

Hi,

Can I get the information?
I will attach the waveform.
If you need more information or if I should clarify my comment ,
please let me know.
Customers are going to make an evaluation with EVM.
However, the EVM can not independently control the EN terminal.
Therefore, customers want to know it.

Best Regards,
Yusuke/Japan Disty

0 Garrett Roecker over 7 years ago in reply to Tsukui Yusuke

TI__Mastermind 21720 points

Yusuke,

The rise time of the waveform is going to be based on the output capacitance. As mentioned before there is no easy way to calculate the rise time of the output. If the enable pin is pulled up separately from the output voltage, there will be a small delay time before switching begins. Once switching starts the the output voltage will ramp from VIN to VOUT. If the soft-start circuit from the application note provided is implemented then this ramp time can be programmed.

Thanks,

Garrett

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LM2623: About output rising time