Can this differential ADC be used to monitor the current of battery charging and discharging?

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zhch_4550981
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10 replies posted 10 questions asked 5 replies posted

differential.pngCan this differential ADC be used to monitor the current of battery charging and discharging?We want to use this to calculate the battery capacity

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zhch,

In my schematic recommendation, you can reading the state of Comp_1's output.  It should be true if charger is present and the voltage of the charger voltage is higher than the battery voltage.  To charge the battery the charger voltage must be higher than the battery voltage.

Len

Len
"Engineering is an Art. The Art of Compromise."

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9 Replies
ShipingW_81
Moderator
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What is the battery used for in your application? mcu power source, or only backup domain power source?

It can complete this work if the battery voltage on within the measurement range. The range depends on the specific settings of component customizer.

Please refer to the guidelines of ADC usage in device TRM documentation and related code example, like -https://www.cypress.com/documentation/code-examples/ce220974-psoc-6-mcu-multi-config-scanadc-example

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I use this battery with a 3.3V DCD

Battery.png

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Len_CONSULTRON
Level 9
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Beta tester 500 solutions authored 1000 replies posted

zhch,

The PSoC cannot read or properly process a voltage below the GND (VSSA) reference.  Therefore if you put a -1.2V source (referenced to the PSoC GND) on one of the pins, the input signal will be clipped.

Can you share your design-intent circuit with with us?  (If using PSoC Creator, you might have an implementation in TopDesign) We need to know the circuit configuration you are using to read the differential signals.

Here's a quick generalization of a charge/discharge current measurement circuit .  The differential measurement is on the "high-side".  This should prevent the input signals from going lower than GND.   However, just like you should have signals going lower than VSSA, you shouldn't have signal going above VDDA on the PSoC.  That is why I included R_3, R_4, R_6 and R_8.  They can scale the input voltage to be within the range of VDDA if needed.

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Len

Len
"Engineering is an Art. The Art of Compromise."
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change or discharge.png

  • Do I still need a -1.2v voltage source?
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zhch,

Do I still need a -1.2v voltage source?

The simple answer:  Yes.

The complex answer:  You must answer this question first.  Can you be sure that VDDA = 5.000V?  Usually not especially if you are powering your PSoC6 from the USB 5V source.  Usually this source is less than 5V and more commonly about 4.75V.

I've attached a TopDesign schematic in a project (no code just schematic) of a redrawn version of your TopDesign. 

As long as your voltage source for VDDA is above 4.25V, the circuit will work to read the current sense for charge or discharge up to 12A (I know, way overkill).  It uses the 1.2V bandgap Vref (a very stable voltage even if VDDA is not stable).  It also eliminates the high value resistors inline to the ADC inputs and eliminates the resistors to GND to prevent extra parasitic currents.  It also includes a comparator to detect if the charging voltage is higher than the current battery voltage.

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Thank you for sharing your intended design.  I hope you won't take offense if I point out a few potential issues.

  • The Schottky diode will prevent unintended discharges into the charging circuit.  However, it will also have a voltage drop when charging anywhere from 0.4V to 0.1V.  This means if your battery is intended to charge to a final 4.25V,  you may need a charging voltage of at least 4.65V.
  • Depending on the chemistry of the battery being charged, there may be a recommended Maximum charge current which varies depending on the state of charge of the target battery.  Usually, the max charge current is lower when the battery is near charge completion.  If your charge voltage is higher than your intended full-charge voltage, you have no controls in your design to prevent over-current charging.  The best you have is R_cs which will somewhat limit the current as the Voltage across Bat_30mA comes close to the charge voltage.  If there is a maximum trickle charge current allowed, you can increase the value of R_cs to prevent over-current charging.
  • Depending on the chemistry of the battery being charged, there may be a recommended Maximum charge voltage.  Right now, your only control of this maximum is the charge voltage supplied.  If this meets the maximum criteria it may not be a problem.

Len

Len
"Engineering is an Art. The Art of Compromise."
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Thanks,

I am sure that VDD=4.25V or 4.35V,Because it came out of a power management chip。My device is a portable device that consists of a charging dock and a monitor, They are separate parts that are connected by pogo pins,The monitor's battery capacity is 23mAh,Its maximum charging current does not exceed 23mAThis power management chip manages the charging voltage and current。

Is this feasible?

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zhch,

It would appear you might be able to connect the battery directly up to the power management chip without the Schottky diode.  What is the recommended circuit from the power management chip manufacturer.

Len

Len
"Engineering is an Art. The Art of Compromise."
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How to detect the successful contact of charging positive electrode without communication,and without the Schottky diode.

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zhch,

In my schematic recommendation, you can reading the state of Comp_1's output.  It should be true if charger is present and the voltage of the charger voltage is higher than the battery voltage.  To charge the battery the charger voltage must be higher than the battery voltage.

Len

Len
"Engineering is an Art. The Art of Compromise."
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