LM27761: LM27661 Inverting operation

taichi

Expert 1395 points

Part Number: LM27761
Other Parts Discussed in Thread: LM2775, TPS63024, LM27762

Hello,

Can LM27661 uses at inverting buck-boost operation?

My Customer is considering by LM27761 at Specification of the following described.

Vin : 2.5~4.2V (Li-Ion)

Vout / Iout : -3.3V / 200mA

Is there the device if they cannot use it?

Regards,

Taichi Nakamura

over 7 years ago

0 Juha Karttunen over 7 years ago

TI__Intellectual 1120 points

Taichi-san,

No boost operation unfortunately. One option would be to use LM2775 to boost battery voltage to 5V and then invert and regulate it to -3.3V with LM27761. Minimum input voltage for LM2775 is 2.7V for 125mA output current and 3.1V for 200mA output current.

Regards,
Juha

0 taichi over 7 years ago in reply to Juha Karttunen

Expert 1395 points

Juha-san

Thank you your reply.
they need output voltege ±3.3V for 200mA.
So, I propose to make 3.6V by TPS63024(buck-boost converter) and LM27662(LDO+Inverting+LDO).

Regards,
Taichi Nakamura

0 Juha Karttunen over 7 years ago in reply to taichi

TI__Intellectual 1120 points

Taichi-san,

Please note 3.6V is not enough for LM27762 if 200mA is needed. Inverting charge pump has 2.5ohm internal resistance, which causes 0.5V voltage drop. Also there has to be enough headroom for the LDO. I would say the LM27762 needs at least 4.0V input voltage for +/-3.3V@200mA output.

Regards,
Juha

0 taichi over 7 years ago in reply to Juha Karttunen

Expert 1395 points

Juha-san,

I understand to need 0.5V voltage drop by inverting charge pump.
Output voltage of buck/boost set to 4.0V.
Thank you.

Regards,
Taichi Nakamura

Power management

Power management forum

LM27761: LM27661 Inverting operation