Capacitor has no effect

[ogedik]

Hi,

I designed a sensor based on ESP32-C3-13 module and sending sensor value over ESPNOW to another ESP32-C3-13. I am facing ~600 - 700mV voltage drop during the send process. In order to solve this problem I attached a 1000uF SMD capacitor close to ESP module. But still having same voltage drop on my scope. If I am not wrong I suppose that I should not see a big voltage drop like 600 mV on my scope. Am I right? Please find scope values attached to the message.

Thank you for your support

[ESP_Sprite]

What is your physical hardware like and how are you measuring?

[ogedik]

What is your physical hardware like and how are you measuring?

I am measuring on C2 SMD capacitor.

[mgsecord62]

I assume that you have looked at the battery voltage and it stays above 3.3 + 0.36(HT7833 typical drop out voltage)= 3.66 volts during this time.
The HT7833 has a max drop out voltage of 0.5 volts at 3.3 volt output.

[ogedik]

I assume that you have looked at the battery voltage and it stays above 3.3 + 0.36(HT7833 typical drop out voltage)= 3.66 volts during this time.
The HT7833 has a max drop out voltage of 0.5 volts at 3.3 volt output.

Hi mgsecord62,

You assumption is looking logical. But there must be a voltage drop behind (before input) of HT7833 if I am not wrong. But I am facing with voltage drop output of the HT7833. Please find my test results at output of HT7833 on my circuit with same battery, below;

With 2500 mAh battery at 4.2V level =>
Voltage drop has occured ~20mV when ESPNOW send process has started which is not a big issue for ESP32.

With 2500 mAh battery at 3.5V level =>
Voltage drop has increase to ~800mV when ESPNOW send process has started which is really a big issue for ESP32.

According to my findings I conclude that 3.5V is not enough voltage level with HT7833 to use ESPNOW. Is it correct? Another question; if it is correct any recommendation to minimize voltage drop at this level?

On the other hand; if we take into account ESPNOW resend process when data has not been acknowledged by destination ESP, this process will take ~1 sec. So under this circumstance it means that we walk around brownout level during 1 sec. As a result of it;

C = I . dT / dV ==>

I = 280 mA (According to ESP32-C3-13 datasheet Tx)
dT = 1000 ms
dV = 1 V

280 (1000/1) = 84000 uF capacitor!!!

So I conclude that I need a super capacitor or ~1F capacitor to use 1xLiPO battery until 3.3v level. What do you think about this? Is it correct?

Thank you for your helps

Orkun

[ESP_Sprite]

I think you're misreading the datasheet, for a Vo of 3.3V the typical dropout only is 350mA. 800mA is for an 1.8V-or-less LDO.

What could be happening is that you run into the internal resistance of the battery itself. In that case, moving the cap to the battery side may help; that keeps a little bit of headroom for the LDO to do its thing while the cap is draining.

(Also, perhaps a stupid question, but are you 100% sure that cap makes good contact with the traces? It looks like the way you soldered it it's possible that one of the pins doesn't make contact but you don't have the clearance to see that.)

[ogedik]

I think you're misreading the datasheet, for a Vo of 3.3V the typical dropout only is 350mA. 800mA is for an 1.8V-or-less LDO.

What could be happening is that you run into the internal resistance of the battery itself. In that case, moving the cap to the battery side may help; that keeps a little bit of headroom for the LDO to do its thing while the cap is draining.

(Also, perhaps a stupid question, but are you 100% sure that cap makes good contact with the traces? It looks like the way you soldered it it's possible that one of the pins doesn't make contact but you don't have the clearance to see that.)

Hi ESP_Sprite,

First of all, thank you for your never ending support and great effort. This support is so much important for a beginner like me. Please find my questions and findings below;

I think you're misreading the datasheet, for a Vo of 3.3V the typical dropout only is 350mA. 800mA is for an 1.8V-or-less LDO.

As far as I know that datasheet has referred that this voltage drop should be occured at input of HT7833. Not output side. This is because output of HT7833 output should be 3.3v in any case unless ESP32 or any other component drop the voltage after that. Isn't it correct? In my case voltage drop only occurs while sending ESPNOW Tx process. My pain point is keeping voltage level stable during Tx at ~3.3v level to avoid brownout on ESP32.

On the other hand, I extect that voltage drop shouldn't be occured at output of HT7833. Because battery voltage is at 3.5v level. Calculation is at below;

3.5v (battery voltage) > 3.3v (HT7833 output) + 360mV ( 3V ≤ VO ≤ 5V in datasheet) . So why do I see 600 - 800 mV drops at output of HT7833?

I just want to understand the basics.

What could be happening is that you run into the internal resistance of the battery itself. In that case, moving the cap to the battery side may help; that keeps a little bit of headroom for the LDO to do its thing while the cap is draining.

It is good idea. I will try this.

(Also, perhaps a stupid question, but are you 100% sure that cap makes good contact with the traces? It looks like the way you soldered it it's possible that one of the pins doesn't make contact but you don't have the clearance to see that.)

This is very good warning. I double checked contacts and traces via continuity check by using multimeter.

Thank you for your patience and best regards,

Orkun

[djixon]

No. You can not bring 3.5V on input of HT7833 and expect to get 3.3V on output.
Internal design of HT7833 requires your input voltage is in the range from 4.3V up to 8V. Anything else, is violating proper operation condition.
Drop out voltage is defined as difference from input and output voltages, which produces 2% drop in output voltage (from nominated value) when Vin = Vout + 1V and with constant load.

So drop out voltage (in datasheet) represents quantity determined for the worst case (which is still in operational range) when Vin = 4.3V