How to configure cell battery and USB power

RE: How to configure cell battery and USB power

hmolesworth — Tue, 23 Jul 2024 15:59:08 GMT

Ah, good point. 3 x 47uF are not that big but I see the problem. 2 x 4.7uF will shorten the useable coin cell battery life, perhaps by 10%, as more of the pulse current has to be supplied from the coin rather than the coin trickle-charging the capacitors and the risk of current-pulse-induced nRF52840 resets will occur sooner. Mitigate by using PPI and keeping the CPU in sleep as much as possible and set VDD to 2.8V. Rapid advertising Tx burst raise the risk of resets, reducing the attempts will also help; instead of (say) 20 Tx advertising per second 1 per second is much better even if then it takes longer to connect. Ditto in Beacon Mode. Worst case change the design to use an external DC-DC battery-to-VDD at 1.8V instead of 2.8V, but that takes as much physical space as 3 x 47uF.

RE: How to configure cell battery and USB power

Serafino Convertini — Tue, 23 Jul 2024 07:20:06 GMT

Hi, if I use 150uF 10V I must use a lot of capacitor and I lost the requirement of smal size :O. At the moment I have 2x 4.7uF 6.3V

RE: How to configure cell battery and USB power

hmolesworth — Mon, 22 Jul 2024 16:25:20 GMT

In case you are not familiar with why I always use 3xvoltage for the capacitor voltage rating as a rule-of-thumb, have a look at this White Paper. 3x is perhaps over cautious, but 2x is mandatory (my view). Ceramics are the only suitable capacitor type, others (Tant, Electrolytic, Super, etc) are too leaky or have short life. Capacitor De-rating Issues nwp_030.pdf

This paper specifically refers to nRF52840 design

RE: How to configure cell battery and USB power

hmolesworth — Mon, 22 Jul 2024 16:02:37 GMT

I would suggest just use your latest circuit as-is, but change the LTC411 to the MAX40203 and set VDD to 1.8V via REGOUT0. Best test before commiting to PCB layout ..

Keep in mind that the coin cell will not work well in low voltage situations (ie below 1.8V + a bit) as REG0 might misbehave, hence the need for large capacitance on the coin cell (and some on VDD).

Edit: VDDH High voltage mode operating voltage 2.5 minimum, so coin cell (as seen at VDDH) must not dip below 2.5V

RE: How to configure cell battery and USB power

Serafino Convertini — Mon, 22 Jul 2024 15:43:20 GMT

Whereas the device must work for long period, if I should use 1.8V as VDD and I have a coin cell with 3V. How could I provide a 1.8V voltage on the nRF. Should I use a DCDC stage to generate 1.8V starting from 3V (coin cell)?

RE: How to configure cell battery and USB power

hmolesworth — Mon, 22 Jul 2024 15:39:07 GMT

Actually provided the coin cell is not used for long periods (the Iq issue) your latest circuit should work well as you can now set VDD to a lower voltage, typically 1.8V, which reduces current drain. However that requires all external peripheral devices (if any) on VDD or a nRF52 port pin to be specified at 1.8V supply, which is generally true nowadays. 1.8V halves the current from a 3.4V coin, and is still pretty good at 2.7V coin; I generally use 1.8V. Note if you have LEDs those require a buck-boost from the battery or a simple voltage doubler from the battery; when on battery power both of those will be required in any case.

What value is the doubled capacitor? I usually recommend low-leakage 150uF 10V on the coin cell, much higher than most reference designs.

RE: How to configure cell battery and USB power

Serafino Convertini — Mon, 22 Jul 2024 15:31:03 GMT

So your proposal is:

using 2x MAX40203 in place of 1x LTC4411 for the less quiescent current;
Connect the VBUS (via MAX40203) to VDDH;
Connect VBAT (via MAX40203) to VDD;
Enabling only the DCDCEN0;

Are you agree?

RE: How to configure cell battery and USB power

hmolesworth — Mon, 22 Jul 2024 15:23:14 GMT

The LTC4411 is a good choice if the battery is not (say) a CR2032 used for long periods; the Iq current (quiescent current to Gnd) is much higher for the LTC4411 (10s uA) compared with the MAX40203 (<1uA) which might not be important if only sparse use on the battery. Using daisy-chaned (ie both) DC-DC is also slightly less efficient, but only a few percent. This becomes an isse if (say) a 1 year shelf-life is required before use.

Both DC-DC need to be enabled by registers, and the VDD output voltage from REG0, via registers DCDEN0, REGOUT0 and DCDEN. The nRFConnect and SDK IDEs are different however, but there are examples.

RE: How to configure cell battery and USB power

Serafino Convertini — Mon, 22 Jul 2024 12:49:00 GMT

I know that the nRF52840 can use linear regulator or dcdc regulator. Using one of them is set automatically or should I set any flag registers?

RE: How to configure cell battery and USB power

Serafino Convertini — Mon, 22 Jul 2024 12:47:58 GMT

Hi, I choose to use LTC4411 to select exclusively VBAT or VBUS and connect the output to VDDH of the nRF

I doubled the capacitors on VDD pin to avoid dropout voltage during radio transmission

RE: How to configure cell battery and USB power

hmolesworth — Fri, 19 Jul 2024 21:33:08 GMT

VBUS from USB complicates things as it is +5V and therefore must connect to VDDH. VDD when VBUS is present will output the programmed voltage on REG0 and so REG0 must be set to the maximum expected CR2032 voltage to ensure no power is taken via the MAX40203 by the CR2032. This implies i/o pins and external circuitry will be at (say) 3.4 volts with VBUS present; internal MCU and RADIO will be 1.3V. With VBUS absent the CR2032 will provide power via MAX40203 to VDD; this implies i/o pins and external circuitry will be between (say) 3.4 volts and 2.6 volts with VBUS not present; internal MCU and RADIO will always be 1.3V. Pulse currents will cause even lower voltages on the CR2032-driven VDD, and so a lot of bulk capacitance is required (ceramic, 3 x 3.4V or say 10V rating). In this scenario, typically the MAX40203 is only required on the CR2032 battery assuming that when VBUS is absent nothing connects to the USB. Adding a MAX40203 to the VBUS input provides better protection against potential back-drive of stuff on the USB port.

The alternative is to use an external 3.4V DC-DC on VBUS and only attach that to VDD with a MAX40203 together with the CR2032 battery; probably a less power-efficient (and more expensive) solution

RE: How to configure cell battery and USB power

Serafino Convertini — Fri, 19 Jul 2024 08:15:10 GMT

Let's assume that using MAX40203 or TCK106 (as used in nRF52840-DK). Does make sense to connect the VBUS (when present) to VDDH and VBATT (qhen present) on VDD, or should I connect the output voltage (VBUS or VBATT) to VDDH?

In both case I think I configure the nRF power stage using internal DCDC.

RE: How to configure cell battery and USB power

hmolesworth — Thu, 18 Jul 2024 16:54:34 GMT

Just replace the two schottkys with two MAX40203; EN is connected to corresponding supply (VBUS or VBATT). Highest voltage of VBUS causes lower voltage to be isolated. ie if VBUS is present there is no load on VBATT; if VBUS is not present VBATT supplies power. EN leakage is tiny. No other hardware or cpu interaction is required.

Edit: EN has an internal pull-up, so don't even need to connect it. Here is example with CR2032; duplicate for VBUS

//                   MAX40203                     
//              In  +-------+ Out    Battery +VE
//        +---------|       |--------------------0
//        |      EN |       |                     
//        |      ---|       |        Battery Gnd 0
//        |         +-------+                    |
//     -------          |                        |
//       ---            |                        |
//        | CR2032      |                        |
//        |             |                        |
//        +-------------+------------------------+

RE: How to configure cell battery and USB power

Serafino Convertini — Thu, 18 Jul 2024 16:45:10 GMT

Ok this IC could interrupt the voltage but how could I use in my application?

RE: How to configure cell battery and USB power

hmolesworth — Thu, 18 Jul 2024 16:38:18 GMT

My grandfather used schottky diodes, nowadays there are better low-drop solutions. Have a look at these:

max40203 Ideal Diode