This is a common question, and the answer is relatively simple. With standard non-synchronous boost converters, there is a direct path between the input voltage to the output voltage. This path consists of the inductor and the forward-biased diode. In the example circuit in the datasheet, you can see the direct DC path will be there even when the boost converter is disabled. When enabled, the converter will perform the switching and regulation function to create a boosted output, as expected.
If the voltage rail sourced by the boost regulator (VBOOST) needs to be controlled, and completely switched off, there are two methods to accomplish this:
- Insert a load switch or simple P-FET in series between VBOOST and the Load.
- Select a Boost Regulator with TRUE SHUTDOWN.
Maxim has a number of High-Efficiency, Synchronous Boost Regulators with TRUE SHUTDOWN:
- MAX17220-MAX17225 for Nanopower Iq applications
- MAX17250 for 18V and below applications
- MAX20471-MAX20473 for 5.25V and below applications
- MAX77231 for low current, ultra-low noise and low ripple
- MAX8815A and MAX1947 for ultra-high efficiency and simplicity from a very low input voltage, to name a few.