LM27761: LM27761DSG failure problem

May I ask whether there is any progress on the problem that the EN pin without limiting current resistor will burn out the chip that was consulted on Monday?

Recently, we have a new product that needs to use the negative pressure chip, so we need to check this design problem as soon as possible, so as to make subsequent decisions.

ANY FEEDBACK? 

Hello user,

Thanks for your question and sorry for the late answer.

The topic of current limiting resistor on EN pin is strictly dependent on the specific device implementation.

Referring to the EVM (Using the LM27761EVM Evaluation Module), you can see that in J1 connector VIN and EN are shorted together, thus it should be fine if you connect directly EN and VIN in your application.

Did you have any actual problem with this connection? 

Please ask again if I misunderstood your question.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

Because we cannot find the root cause of the damage of LM27761, we temporarily suspect that this chip is not suitable for our application scenario.

Our negative voltage is mainly used as the negative power supply for the op-amp and the reference input voltage for the op-amp. The output of the op-amp is also negative, and the output of the op-amp supplies power to the CMOS sensor.

Please help to recommend the negative power chip. It is better not to operate in this charge pump mode. The requirements are as follows: the input voltage is 3.3V, the output voltage is -3V to -5V, and the output current is greater than 220mA;

The volume is best within 3*3mm, the peripheral circuit does not need inductors, diodes and other large package devices is best;

EN is a high-impedance CMOS input. As long as you stay inside the limits shown in the Absolute Maximum Ratings, no current will flow. This is not the cause of your failures.

A charge pump inverter with a single flying capacitor cannot generate a voltage whose absolute value is higher than the input voltage. Additionally, the output impedance of the inverter will limit the voltage further (at 220 mA, the voltage drop will be more than 500 mV). The LM2682 is a doubling inverter, but does not provide enough current. You need an inductor-based inverter like the TPS63700 or LMR70503.

Hello User,

as Clemens previously stated, you cannot use LM27761 to obtain a voltage whose absolute value is higher than the input voltage, due to its working principle.

If you need a device with that characteristics you should check the Inverting converters in: Buck/Boost Regulator | Inverting Buck/Boost | Overview | TI.com

In particular TPS63700 and LMR70503   could be suitable for your solution, as Clemens observed.

Unfortunately for these type of topologies you need to place an inductor externally.

Please ask again if you have any more questions.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

Hi Clemens,

Thank you very much for your input.

Best regards,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

Please tell me. For example, the maximum output current of LM27761 is 250mA. Does this chip have the ability of sink current?

Hello User,

Thanks again for your question.

Can you please better clarify what you mean by that?

The device sinks current from the output during shutdown, when it discharges the output capacitor.

Referring to the datasheet:

Instead during operation, if the load injects a current in the output capacitor that causes the output voltage to rise (in absolute value), I don't think that the devices would be able to keep Vout regulated anymore.  In order to confirm that, I would need to run same lab measurements, since I don't have first hand experience with the topic.

However, referring to your previous question, LM27761 is not able to satisfy your specifics since you need an output voltage larger (in absolute value) that the input one.

If your specs are still the same, I would suggest you to have a look at   TPS63700 and LMR70503,that could be more suitable for your application.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).