LMP91000: Calculate the Vout is not right

felix.he

Part Number: LMP91000

Hello ,

As the picture above, I config Rl0ad=100 ohm, Rtia=2.75k ohm, zero_int=67%,Vias=10%, Vref=2.5V(external),then I measure the Vwe=1.438V,Vre=1.433V,Vout=1.838V, How the Vout get the 1.838V?

This is not match the LPM91000 block.

Can you please help explain?Thansk!

I2c1_Write_Byte(LPM_ADDRESS,REG_LPM_LOCK,0);
I2c1_Write_Byte(LPM_ADDRESS,REG_LPM_TIACN,0x07);
I2c1_Write_Byte(LPM_ADDRESS,REG_LPM_REFCN,0xD6);
I2c1_Write_Byte(LPM_ADDRESS,REG_LPM_MODECN,0x03);
I2c1_Write_Byte(LPM_ADDRESS,REG_LPM_LOCK,0x01);

over 8 years ago

0 William Santos56 over 8 years ago

TI__Prodigy 390 points

Felix,

Try writing your configuration bytes to the correct TIACN register address, which is 0x10 not 0x07. REFCN is at 0x11, MODECN 0x12, LOCK is 0x01. Does this help?

Regards,

Will

0 felix.he over 8 years ago in reply to William Santos56

Prodigy 120 points

Hi Will,

Thanks! But my address is correct, The 0,0x07,0xD6,0x03,0x01 are data to be written to register.

The oxygen sensor output voltage from 0mv to 80mv , is my config wrong(Rl0ad=100 ohm, Rtia=2.75k ohm, zero_int=67%,Vias=10%, Vref=2.5V(external))?

If it is right , how to calculate the Vout from We and Re?

Thanks very much!

Regards,

Felix

0 William Santos56 over 8 years ago in reply to felix.he

TI__Prodigy 390 points

Felix,

Refer to Figure 26 in the datasheet for correct wiring of your 2-lead oxygen sensor. Refer to Figure 24 for a 3-lead sensor. Are you configuring the cell as 2-lead or 3-lead?

Will

0 felix.he over 8 years ago in reply to William Santos56

Prodigy 120 points

Hi Will,

3-lead(3-lead amperometric cell).

Thanks!

Regards

Felix

0 William Santos56 over 8 years ago in reply to felix.he

TI__Prodigy 390 points

Felix,

In that case, shorting the Re and Ce pins is not necessary. What is the intended purpose of Q11 in your design? Try removing it from your design and taking your Vout measurement again. Thanks

Regards,

Will

0 felix.he over 8 years ago in reply to William Santos56

Prodigy 120 points

Hi Will,

Still got the same measure result after removing the Q11.
Does the voltage input can use mode 3-lead?
Can you show me the applition of voltage to voltage work in mode 3-lead?
Thanks a lot!

Regards,

Felix

0 William Santos56 over 8 years ago in reply to felix.he

TI__Prodigy 390 points

Felix,

Did you remove the short circuit between Re and Ce? Do that as well. This will correctly configure your schematic to a 3-lead amperometric cell. Vout is related to We as follows from your schematic:

Vout = (Vref_div) – (RTIA × Iwe)

I suggest removing the external resistor between C1 and C2 unless you require a specific gain that is not achievable with the pre-programmed RTIA. Thanks

Regards,

Will

0 felix.he over 8 years ago in reply to William Santos56

Prodigy 120 points

Hi Will,

Thanks for your help.

Finally , I changed the mode to 2 lead amperometric cell, and it work.

Regards,

Felix

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LMP91000: Calculate the Vout is not right