STEVAL-ESC002V1 and STSPIN32F0A 2S configuration

[FRagg.1]

Hi,

we implemented your reference design coming from the STEVAL-ESC002V1 that is suitable for 2S to 6s battery.

We found that the circuit didn't work under the 6.5Volt and we have the confirmation of this out of spec because STSPIN32F0A is working from 6.7V.

So how can we use the circuit with the 2s conf? The minimum working voltage expected for 2s conf is at leas 6V.

Can you help me to understand how to modify the project to support low minimum voltage (6v)?

Can be possible to modify the firmware?

[Cristiana SCARAMEL · Accepted solution]

Hello @FRagg.1​,

The nominal voltage is the default, resting voltage of a battery pack, for 2S is 7.4 V (3.7 per cell). 

It is not, the full charge voltage of the cell, in fact the LiPo batteries are fully charged when they reach 4.2 V/cell.

The minimum safe charge is 3.0 V/cell. A LiPo cell should NEVER be discharged below 3.0V, it is not recommended using the battery at this value. 

For this reason in most of speed controls a Low Voltage Cutoff (LVC) detects the voltage of battery pack and alert the user in case of low voltage.

Moreover, keep in mind that the battery voltage change with the temperature.

Basically, it is not possible to use the whole battery charge, but under nominal conditions the board is operational up to about 80% of the charge at room temperature.

Let me know if I addressed your concerns, if so please "Select as Best" button.

[FRagg.1]

Buongiorno Cristiana,

cambio lingua in quanto immagino che siamo entrambi italiani.

Capisco le tue osservazioni, ma il chip (STSPINxxx) dichiara che come tensione minima di funzionamento (VM) per il fornt end analogico è di 6.7 volt che è ben superiore a due celle da 3v in serie. Per questo mi sembra non in specifica con ciò che dichiarate. Anche pensando di non arrivare alla tensione minima di funzionamento, siamo a rischio di disattivazione degli ESC nel caso in cui la batteria dovesse avere un aumento di carico che si tradurrebbe in uno spike di discesa di tensione.

Grazie. Come work around ho pensato di metterci un booster di tensione su VM e piantarlo a 7.5V. Ci vedi controindicazioni?

[Cristiana SCARAMEL]

Hello @FRagg.1​,

I translate your answer (google translate) for others community users.

<< I understand your observations, but the chip (STSPINxxx) states that the minimum operating voltage (VM) for the analog supply is 6.7 volts which is well above two 3v cells in series. For this it seems to me not in specific with what you declare. Even thinking of not reaching the minimum operating voltage, we are at risk of deactivating the ESCs in the event that the battery should have an increase in load which would result in a voltage drop spike.

Thank you. As a work around I thought of putting a voltage booster on VM and planting it at 7.5V. Do you see any contraindications? >>

The 6.7 V is the minimum turn on threshold for the STSPIN32F0A IC.

In the case you described you should refer to the UVLO turn-off voltage max 6.4 V (typical value 6.1 V).

The device enters into the undervoltage condition when the power supply voltage falls below the off threshold voltage and expires when the motor supply voltage goes over the on threshold voltage. If you have a proper tank and by-pass capacitors on the VM supply any voltage drop due to the load variation should not cause problems to the device.

No contraindications in adding a boost to the VM.

Pay attention to the absolute maximum ratings of the device, in particular the power stage supply voltage must not exceed the VM pin voltage.