BQ76952: LDO without output when battery drop below 1.5V

Hello User,

That is not what the datasheet is trying to explain. That was the test condition to test for the headroom of the BJT pre-regulator. But the required headroom voltage can be 1.91-V at most.

If using the BJT pre-regulator, there is an overhead voltage required for it to regulate REGIN correctly. For example, to ensure that we maintain a LDO voltage of 3.3-V, the REGIN voltage should be greater than ~4.1-V (as per datasheet specs).

In order to maintain ~4.1-V on the REGIN pin with our pre-regulator, the collector voltage would need to be ~6.7-V. (VBE + 4.1-V + VBREG_HDRM = 0.7 + 4.1 + 1.91 = ~6.7-V). This is the voltage requited on the collector of the BJT to ensure that REGIN gets the right voltage on the pin.

With 4s system and 1.5-V a cell, you would only get ~6-V of stack voltage, which probably would drop further in voltage if you have a diode to the BJT path.

If you want the LDO to work properly with this low voltage, you would require a different step-down circuit.

Best Regards,

Luis Hernandez Salomon