TLV1117: TLV1117-ADJ output problem

Hardy Ma

Part Number: TLV1117
Other Parts Discussed in Thread: LM117

Hi TI team，

My application：Vin = 5V，Vout = 2.8V，Iout = 0.5A；

Describe：I use TLV1117-ADJ for simple testing. By calculating, R1 and R2 value use 3.9K, Cin and Cout and Cadj is no addition.

By testing found, the output voltage increases with the input voltage, the dropout voltage stay in 0.8V.

Please help to analyze the reason. Many thanks.

over 7 years ago

0 Ryan Eslinger over 7 years ago

TI__Guru 55940 points

Hi Hardy,

Do you have any scope shots that you can share of Vin, Vout, and Iout to help us debug.

Is it possible that R1 does not have a solid connection or that there is an unintentional leakage path that could be impacting the output voltage such as excess flux?

Very Respectfully,
Ryan

0 Hardy Ma over 7 years ago in reply to Ryan Eslinger

Intellectual 470 points

Hi Ryan，
Thanks for your reply.
If the output voltage is 2.8V, the feedback resistance chooses how much value is appropriate?
Is R1 = R2 = 3.9K appropriate?

0 Ryan Eslinger over 7 years ago in reply to Hardy Ma

TI__Guru 55940 points

Hi Hardy,

You may be able to improve your accuracy by reducing the size of resistors. The reason this will help improve accuracy is because by reducing the resistor values, you will be increasing the current through the resistor divider. This reduces the effect of any change in Ifb because Ifb will become more negligible as the resistor divider current increases.

Very Respectfully,
Ryan

0 kai klaas69 over 7 years ago

Guru 140200 points

Hi Hardy,

your programming resistors are much too high. Take 240R for the upper resistor. Remember that minimum load current of TLV1117 is 5mA. Minimum reference voltage is 1.2V. So, the upper resistor should be 1.2V / 5mA = 240R. It's like designing the LM117.

Kai

0 Hardy Ma over 7 years ago in reply to kai klaas69

Intellectual 470 points

Hi，
Thanks.

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TLV1117: TLV1117-ADJ output problem