During shutdown, the battery input is connected to the output through the inductor and the internal synchronous rectifier of the MAX8569. This allows the input battery (rather than a separate backup battery) to provide backup power for devices such as an idled microcontroller, SRAM, or real-time clock, without the usual diode forward drop. Drive SHDN to VOUT (logic-high) to enable the IC for normal operation.
If the voltage rail sourced by the boost regulator (VOUT) 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.