LTC4121can't work if the input voltage under 15V.The design is according to the datasheet of LTC4121.But it works only the input is above 15V.It can't work if input under 15V(for example 9V in the schmatic) .please hep me
We have seen strong sensitivity of the operation of the LTC4121 to the physical placement of the capacitor at IN, capacitor at INTVcc and at BOOST. Improper placement can lead to the INTVcc voltage being pumped down by chip operation, leading to a UV lockout on the INTVcc voltage. In this scenario, the LTC4121 may rapidly cycle between on and off. A typical symptom of this problem is limited range of the input voltage; over certain input voltages, the LTC4121 will appear to stop working completely, or may charge at a much lower rate than programmed. The presence of this problem can be confirmed by applying an independent 4.3-5.0V, bypassed power supply between INTVcc and GND which will overpower the internal INTVcc. If the circuit behaves as expected with the independent supply, the problem is due to less-than-ideal placement of one or more of the 3 capacitors. The designer can review the DC1977A demo-board layout for a successful capacitor-placement strategy.
Here’s the location of the DC1977A design files. http://www.analog.com/media/en/reference-design-documentation/design-integration-files/DC1977A_with_Rework.zip
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