The OPAMP bus clock (CLK_OPAMP_APB) can be enabled and disabled in the Power Manager, and the default state of CLK_OPAMP_APB can be found in the Peripheral Clock Masking.
A clock (CLK_ULP32K) is required by the voltage doubler for low voltage operation (VCC < 2.5V). The CLK_ULP32K is a 32KHz clock which is provided by the OSCULP32K oscillator in the OSC32KCTRL module.