10/12/2016 7:19 PM
Dear,

1. Vin = 5V (from 5V - 3A DC/DC power). Vin_lim is set at 4.65V, is it ok ?
2. I am not clear about input voltage limit function.
- With Vin = 5V, if Vin_lim is set > 5V - what happen ?
- With Vin = 5V, if Vin_lim is set < 5V - what happen ?
3. In datasheet, "When the voltage on VLIM pin hits the reference voltage of 1.52V, the output of the input voltage limit error amplifier will drop in to control the operation duty. In this mode, the input voltage will be clamped according to the value set by the resistor divider"
- What mode is in normal condition, VLIM pin > 1.52V or VLIM < 1.52 V ?
- Input voltage will be clamped - you mean Vin will be clamped ?
4. In our current design, Vin = 5V, Vin_lim = 4.65 V, Vsys = 4V, L = 1.2uH, Cout = 22u.

- Big ripple in Vsys (attached waveform), without battery inserted.

- Vin = 5V , adjust VILIM pin voltage > 1.52V.

- Vin = 5V, adjust VILIM pin voltage < 1.52V.

Thanks,

Nguyen Tran

 10/14/2016 6:01 PM

Nguyen,

The main purpose of Vin limit is to ensure the source voltage doesn't drop below certain set limit when the device is drawing power higher than the source's maximum power. Therefore, when the input voltage drops below the voltage limit, the regulator will operate in separate loop to prevent Vin drops below the set voltage.

At normal operation, the Vlim should be greater than 1.52V. At abnormal condition (e.g. a 5V source with 5W power), if the regulator is drawing 2A from the source, then the source voltage will be pulled lower. When it reaches the Vlim, the device will operate in another loop which clamp the Vin above set voltage in order to prevent over drawing power.

At your case, if Vin=5V, and Vlim is purposely set above 1.52V, then the regulator may be trying to keep the Vin above 5V, which cannot be done.

Thanks,

Kevin

 10/26/2016 10:04 PM

Hi Kevin,

With setting (Vin = 5V, Vsys = 3.9V)

- With battery pack inserted, Vsys is Ok

- But without battery pack inserted, Vsys output get big ripple. is it normal ?

Regards,

Nguyen

 10/27/2016 4:19 PM

Nguyen,

Please try to add a 22uF cap on BATT. It may help on the Vsys.

Thanks,

Kevin

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