BC127 Minimum operating voltage


#1

Hello, all

In my application, I plan to use the BC127 and my main power supply is 3.0V (with no battery connection)

I’ve noticed that the minimum working voltage of the BC127 IS 3.1V because of VCHG specification:
There is an example of a fixed voltage configuration, similar to my application:

Now, I don’t understand one thing, If I don’t use the battery charger function, why still connect the related charging pins (VCHG, VBAT_SENSE) to the power supply even though there are disabled?

Why limit the module’s minimum working voltage to VCHG specification if it not in use…?

Can I simply connect my 3.0V power supply to VBAT and VDD_PADS? (no USB connection is required)

Thanks a lot!

Nir


#2

Hi,

The PTS (product technical specification) actually states that the operating voltage range is as per the normal Li Ion range of 3.3V to 4.7V since, as with most thing, it is primarily designed around handsets which revolve around these batteries.

https://source.sierrawireless.com/~/media/support_downloads/airprime/hardware_specs_user_guides/41110693%20bc127%20pts_r1.ashx

Regards

Matt


#3

Hi Matt
Sorry, I don’t accept your answer…
The PTS (product technical specification) also states that the operating voltages are lower than 3.3V (see table 4-1).
So, which one would you refer to?

Thanks,
Nir


#4

Nir,

I am referring to the basic electrical characteristics of the device stated in table 1-4 which is the benchmark and for which the unit is rated. I suspect that 4-1 is giving the minimum voltages for the actual chipset which in theory the unit can work with but there are no guarantees. It is the same for a lot of the WWAN chipsets as well where the base band can actually go down to 2.8V (and in some cases 1.8V) but we state a voltage of 3.3V as this enables us to guarantee operation within the specification.

Regards

Matt


#5

Matt,

Too bad there is no clear reference on the specification page, whether the spec refers to the module or to th chipset inside - and by the way, other modules like Silabs WT32i, or Laird BTM511, do specify very clear that operating voltages are below 3V, and there are no disclaimers about guaranteed operation.

Tell you the truth - as someone who is going to choose a module for my next product, I would not rely on technical specifications that detail different data without clearly explaining the conditions under which the component was tested for 100 percent reliability.

Thanks anyway for your reply.
Nir


#6

Hi, in this particular power supply scenario VCHG is also a module enable pin as the module will boot when the voltage on VCHG exceeds 3.1V. There are actually multiple fixed voltage supply configurations, we only included one (the one we extensively tested) to avoid confusion and bespoke device configuration as each supply configuration requires a different set of configuration parameters to work properly.

If we haven’t put you off the BC127 due to the documentation i’d be happy to look into a supply configuration that suits your needs and what the impact to the device configuration would be.

Kind Regards

Justin


#7

Hi Justin,
Thank you for your answer.
My main goal is to get low as I can get, in terms of battery voltage. meaning - as low as 3.1 - 3.2V.
Than I plan to use a 3.0V LDO to power the module, and obviously I need an extra 100-200mV above the LDO output voltage.
If I don’t supply VCHG at all, the module wont work?
Isn’t the VREGENA pin supposed to enable the module?

If VCHG is mandatory, it is possible for me to use 3.1V LDO - but its not the best solution.

So, my “best case” hardware design would be to use a single 3.0V as main supply (including logic levels), the “worst case” would be to use 3.1V as main supply, and include another 3.0V LDO for VCC_PADS logic levels.

What do you suggest?
Thanks again,
Nir


#8

Hi Nir, VBAT input support is minimum 2.8V so using a 3.0V LDO will be fine to supply the module. In this scenario, VBAT_SENSE, CHG_EXT & VCHG should be left disconnected and supply connected to VBAT alone. VREGEN is used to start the module however, it must only be driven once the input supply is stabilized (VREGEN pin voltage reference is VBAT), a 5ms delay is required post applying input voltage to VBAT before VREGEN is driven high. The recommended delay circuit if you are using the supply to the module as a reference for the delay is below. If VREGEN is controlled digitally from a PIC or HOST then you can add the delay in the controller.

Schematic snippet says 3.3V but is also valid down to 2.8V

image


#9

You can also use the same LDO to power VDD_PADS.


#10

Hi Justin,
Great! this is exactly what I wanted to hear.
I have some experience with BT modules that includes CRS’s Bluecore chipset, and it was a little strange when I read the BC127 spec - regarding the 3.3V operating voltage…
By the way, the VREGENABLE specification is also familiar to me - Thanks for the refinement.
I strongly encourage your company to add to the product’s datasheet some more details about the option I am implementing, it will help you in sales :slight_smile:

Thanks again for your help.
Nir
P.S. Jastin - could you please specify your job description is sierra?


#11

Hi Nir, i agree with your comment about providing better datasheet for BC127 and we are in progress of updating all the BC127 documentation to do so.

I’m the Senior Manager of the Short Range R&D development team in Sierra Wireless, a hardware engineer by trade.

Best Regards

Justin


#12

Hi Justin,
Glad to hear that you made a decision to update the datasheet, and thanks for your reply.

Best Regars,
Nir