Heat generation of REG710NA-3.3

Takahiro Nishizawa

Genius 5575 points

We have a question about REG710NA-3.3.

Please tell us the formula of heat generation.

Vin, Vout, Iout, RΘja.

What information do we need to calculate the heat generation?

For example ,LDO :

(Vin-Vout) x Iout x RΘja

Best regards,

Takahiro Nishizawa

over 6 years ago

0 Julian Hagedorn over 6 years ago

TI__Mastermind 20900 points

Nishizawa-san,

you need to first calculate the power loss inside the device which depends on your specific input and output voltage. You can calculate the power loss with:

Ploss = Pin*(100%-efficiency)

From this you can calculate the temperature increase.

regards,

Julian

0 Clemens Ladisch over 6 years ago

Guru 316440 points

Assuming that the charge pump works in boost mode (V_in is less than 4.0 V), it simply doubles the input voltage and then gets rid of the remaining voltage like an LDO.

Therefore, the efficiency is approximately V_out / (2 × V_in) (see section 8.4.2 of the datasheet), and the temperature increase is approximately (2 × V_in − V_out) × I_out × R_ΘJA.

The efficiency becomes noticeably worse at small load currents:

0 Takahiro Nishizawa over 6 years ago in reply to Clemens Ladisch

Genius 5575 points

Thank you for your support!

Increasing temperature : (2 x Vin - Vout) x Iout x RΘja

Is this understanding correct?

efficiency=Vout / (Vin x 2)

Why does this formula change to (2 x Vin - Vout) in the formula of increasing temperature?

Is efficiency not related to the formula of increasing temperature?

Best regards,

Takahiro Nishizawa

0 Clemens Ladisch over 6 years ago in reply to Takahiro Nishizawa

Guru 316440 points

The input current is double the output current, so P_in = V_in × 2 × I_out. Therefore,

P_loss	= P_in × (1 − efficiency)
	= V_in × 2 × I_out × (1 − V_out / (2 × V_in))
	= 2 × V_in × I_out − I_out × V_out × (2 × V_in) / (2 × V_in)
	= (2 × V_in − V_out) × I_out

0 Takahiro Nishizawa over 6 years ago in reply to Clemens Ladisch

Genius 5575 points

Thank you for your answer!

We understand the formula of Ploss.

Increasing temperature=Ploss x RΘja

Is this understanding correct?

Best regards,

Takahiro Nishizawa

0 Clemens Ladisch over 6 years ago in reply to Takahiro Nishizawa

Guru 316440 points

Yes.

Power management

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Heat generation of REG710NA-3.3