Hello,
I have an application with the following specs:
- Input voltage: 2 AAA alkaline batteries, so [ 2 to 3.2 ] V.
- Output voltage: 3.3 V
- Output current: can be 10mA, 30mA or 60mA.
- The TLV61220 is normally off and it is powered only when is necessary to supply the circuit.
Using the recommended components in the datasheet, the output voltage drops to 2.9V when the input voltage is between [2.9 - 3.1]V and the load is consuming 30 mA, for any other voltage range [2 - 2.9]V and [3.1 - 3.2]V the output is stable at 3.3V. In this case (30mA consumption), increasing the inductor value to 10uH, stabilizes the output for 3.3V for all the desire input range.
For a 60mA load, I can only get stable 3.3V output from [2.1 - 3.2]V by using a 15uH inductor and a lab power supply, increasing the inductor worsens the results (even if the output capacitor is increased). Using the AAA batteries instead of the lab power supply, the behaviour of the circuit (post-tlv61220) is not the one expected below 2.5V.
What may be the cause for this behaviour? Is it possible that the TLV61220 entering into discontinue mode in any of these cases and that may cause this effect? Can it be layout problems? The 4.7uH inductor should be just enough for my needs (at least until 2.2V), correct? Finally, any thoughts why alkaline batteries have such poor results when compared with a lab power suplly?
Many thanks for any advice.
Miguel
