Battery powered wearable, lowest possible V_in for 3.3V V_out?

Integrated Inductor Power Modules
1

Hello,

I’m considering to use the MPM3810 or MPM3820 for a battery powered and wearable controller. The system requires a single 3.3V rail capable of >1A, thus the aforementioned chips seem suitable. But I noticed that only the MPM3820 is “ideal for single cell Lithium batteries”. But I could not find any difference apart from the value of the integrated inductor and a lower R_dson. Is there more to this?

I’m also wondering about the chip’s behavior when V_in approaches V_out. If V_in reaches 3.3V, will it enter 100% duty cycle and remain stable? Or should there be a save delta voltage between the in and output, and how big would this be? A smaller minimum delta results in more usable capacity of the battery, which is very valuable to my compact design.
Is its stability at low delta effected by whether it’s a fixed output or has external feedback resistors?

Thank you in advance for your time and help.

Kind regards,

Theo

2

Hi @tpbruinsma,

The MPM3810 and MPM3820 are essentially the same device with one being capable of handling more current which will be the MPM3820.

When the Vin close to Vout, the low side MOSFET turns off. This doesn’t allow either of the devices to enter DCM. If DCM is requires, the off-time of the low-side MOSFET in continuous conduction mode (CCM) should be longer than 40ns. It means the maximum duty is 95% to guarantee DCM mode at light load.

Thank you
Saurabh