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Boost Mode TON_MAX

In Boost mode, the BB_TON_MAX field in the LDOC_BB_CTRL register should be set to a non-zero value to ensure a finite on-time

under all conditions. Without this protection, in certain scenarios (e.g., where the inductor peak current may be limited by battery impe-

dances and inductor and power train resistances), the inductor current may not reach the threshold of the peak current detector and the

Boost converter power train NMOS will not turn off.

3.2.1.6 Boost Mode TOFF Maximum Limiting

In certain scenarios, the battery voltage at the input to the EFP01 in boost mode can be as high as, or higher than, the desired output.

For example:

• A Li/FeS2 battery can have an output voltage as high as 1.8 V at the very start of its life, which would be problematic in an applica-

tion where the regulated output needs to be 1.8 V.

• Two alkaline or Li/FeS2 batteries in series can provide a voltage as high as 3.6 V. If a 3.3 V regulated output is desired, the buck/

boost configuration can be used, but the buck/boost configuration efficiency is ~5-8% less than the wired boost configuration.

A PFM converter, such as the EFP01, cannot typically operate in a boost mode with an input voltage even slightly higher than the out-

put. In this scenario, the inductor current during the TOFF interval may never reach zero (a requirement for the converter to signal the

end of the discharge phase), resulting in an inaccurate and poorly regulated output voltage.

To address this issue, the EFP01 has a TOFF maximum limiting feature to enforce a maximum discharge interval time. When the

BB_TOFF_MAX field in the BB_CTRL6 register is set to a nonzero value, the TOFF discharge interval is ended after a set period of

time, even if the inductor current has not reached zero, with any residual inductor current is discharged into the VOA pin.

To avoid extremely large ripple voltage, TOFF maximum limiting should only be enabled when the maximum battery voltage is no higher

than 0.3V above the programmed VOA voltage.

EFP01 Energy Friendly PMIC Family Data Sheet

System Overview

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EFP01 Datasheet(PDF) 15 Page - Silicon Laboratories