CN0510: Handling Battery with Higher Voltages

Hi,

  TIP31BG is used in the Darlington pair which allows VCE upto 10V (since its Vcc = 10V). For batteries with 12V, some other power transistor with VCC >=12V must be used for the Darlington pair.

TIP31A - Complementary Silicon Plastic Power Transistors (onsemi.com)

Says TIP31BG can stand max of 80 VDC. 12 should be no problem. No?

Hi,

• The TIP31BG is an 80V device, so that’s one limitation.
• The limit is the voltage ratings on capacitors C36/37/38/39 used in EvalAD5940BATZ board which are 10V devices.

Hence VCE voltage is restricted to 10V max.

OK - although those caps are effectively connected in series and might take 20 volts.  Looking at it, I now wonder about the ADG636. The absolute max input voltage is specified as VDD +0.3 volts. During connection or disconnection of a battery, it might see a momentary spike as high as the battery terminal voltage. Is there any built-in protection for this? 

There is a low pass filter (marked by LPF0 in schematic) at the input of ADG636 that doesn't allow spike voltage to reach the IC.

Yoi may refer to EVALAD5940BATZ schematic here: CN0510 User Guide [Analog Devices Wiki] for circuit at input of ADG636.

Sorry. I don't see how this protects the 636.  I can understand that this prevents sustained voltage from appearing at "sense_p" but it seems to me that C39 and R2 actually form a high pass filter that would provide a nice transient into pin 11 of the 636.

The situation I am thinking of is where F- S- are connected to the battery (and hence AGND) and then you connect S+ F+..  The point SNS_P momentarily rises to the full battery voltage relative to AGND.  As C9 and C36 charge up, this voltage difference decays.

I think the only thing that protects against this is the 1K resistor R8 and any built-in protection diodes on the inputs of the 636. Looking at the spec sheet, I see that there are supposed to be such diodes. Max current spec is 20 ma for 1 ms. So perhaps the inputs are protected up to about 20 volts. 

I am telling about the LPF0 wire connected to input of ADG636, not the series cap.

You may search for LPF0 in schematic. 

In the schematic that I have, there is no connection from LPF0 to ADG636.

Perhaps you mean via 2.2 Meg resistors R2 and R3?  

LPF is highlighted:

Yes, I see. My point is that since the connection to ADG636 inputs via 2.2 M resistors, it offers no protection against fast transients coupled via C38 or C39.  I think the 1K series-connected resistors R7 and R8 combined with the built-in protection diodes produce the protective effect.  The only question is how much voltage this can withstand. I was guessing 20 volts, which means a 24-volt battery might be too much.

Hi,

I wish to direct you to this document: Using Electrochemical-Impedance Spectroscopy to Image Failures in Hydrogen Fuel Cells | Analog Devices

which shows how current excitation can be extended in CN0510.

Hi,

I wish to direct you to this document: Using Electrochemical-Impedance Spectroscopy to Image Failures in Hydrogen Fuel Cells | Analog Devices

which shows how current excitation can be extended in CN0510.