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LTC3261 output voltage lose

Hi ADI experts,

I use LTC3261 inverting charge pump to generate a negative voltage which supplying OPA AD8009ARZ.

Each LTC3261 providing 4 OPAs.

In my experiments, the input voltage of LTC3261 is +5V, and the pin RT = 0, pin MODE = 0, then LTC3261 operates in 500kHz constant frequency.

The output voltage of LTC3261 should be -VIN = -5V.

But I noticed that the output voltage only -2.9V.

While I remove all OPAs, the output voltage of LTC3261 is -5V which is expected.

Then I add 1 OPA in my experiments, the output voltage of LTC3261 is -4.5V, adding 2 OPAs the output voltage is -4V, and adding 4 OPAs the output voltage is -2.9V.

In other words, the output voltage loss 500mV by adding one OPA.

Besides, I use a power supply to provide -5V voltage to OPAs, I measured the -5V power consumption is 70mA.

The 70mA should be fine for LTC3261, it describes up to 100mA output current in the specifications.

Below is my schematic and experiments.

The yellow trace is Vin and green trace is Vout.

Below is the measurement between flying capacitor 1uF.