BOOST efficiency and quiescent current consumption depend on the operating mode.

In Auto mode, BOOST switches automatically between High Power, Low Power, Ultra-Low Power, and Pass-through modes. In Low Power and Ultra-Low Power modes, the average output voltage of BOOST is 50 mV above the target level.

BOOST can be blocked from entering High Power mode (NOHP). In this case, it will automatically choose between Low Power, Ultra-Low Power, or Pass-through mode.

BOOST enters Pass-through mode when battery voltage is at least 100 mV above the target VOUT.

Exit criteria from Pass-through mode depends on the following settings:

  • Auto or High Power – BOOST exits to High Power mode when VOUT drops 50 mV below the target VOUT
  • Auto, No High Power or Low Power – BOOST exits to Low Power mode when VOUT falls below target VOUT +25 mV for longer than 30 μs

BOOST can be forced to High Power, Low Power, or Pass-through modes through registers BOOST.GPIO, BOOST.PIN, or BOOST.OPER. When forced to High Power or Low Power mode, it can still enter Pass-through mode. When in forced Low Power mode, Ultra-Low Power mode is not available.

Note: A GPIO pulled HIGH should request for a lower power mode. For example, GPIO HIGH=Low Power (host sleeping) and GPIO LOW=High Power (host active). This ensures that the host is supplied when a host reset occurs.
Figure 1. BOOST operating modes
Boost operating modes

High Power mode

High Power mode has the highest output current capability IVOUT_MAX and highest quiescent current IQHP.

Low Power mode

Low Power mode provides less output current but also consumes much less quiescent current IQLP compared to High Power mode. See Figure Load current triggering mode change vs. VOUT for details.

Ultra-Low Power mode

Ultra-Low Power mode has very low quiescent current consumption IQULP.

Pass-through mode

Pass-through mode has very low quiescent current consumption IQPT and can provide output current up to IVOUT_MAX_PT.

In case Pass-through is a valid operating mode for the application (e.g. a fresh battery has higher voltage than target VOUT), it is strongly recommended to set BOOST in Auto mode. The only additional configuration needed is the setting of the output voltage either by using pin VSET or register BOOST.VOUT. Once battery has been discharged and its voltage falls, BOOST automatically exits the Pass-through mode to regulate the output voltage.

In order to use forced Pass-through mode, BOOST output voltage VOUT has to be first configured to the minimum setting (1.8 V) and only then forced Pass-through mode is to be set in register BOOST.OPER. Forced Pass-through operation continues until the mode is changed by the host, even if battery voltage falls below 1.8 V.