TLV369: Negative Voltage measurement using ADC

Arvind

Part Number: TLV369

Tool/software:

Hi everyone,

I'm trying to measure a -15V output from a DC-DC converter using the inbuilt ADC of an MCU, which operates on a 0-3.3V range. To scale down the voltage, I plan to use a TLV369 op-amp powered by 0V and 3.3V (no negative rail available, and I prefer not to add one).

How can I design the circuit to measure the -15V effectively with these constraints?

9 months ago

+1 Clemens Ladisch 9 months ago

Guru 317480 points

This circuit maps the range −15 V … 0 V to the range 0.15 V … 3.3 V.

+1 Ron Michallick 9 months ago in reply to Clemens Ladisch

TI__Guru**** 165626 points

Arvind,

If you want to modify the circuit for a different transfer function, you can use excel calculator tool below

/cfs-file/__key/communityserver-discussions-components-files/14/2112.Voltage-Scaler-Calculator_2800_1.02_2900_.xlsx

Use Non-inverting Calculator tab. Circuit #2 makes the circuit above based on desired ranges.

Step 1: Enter Data	Point 1	Point 2
VIN voltage	-15	0	<-- Use [min and max] VIN range
VOUT voltage	0.15	3.3	<-- Use VOUT for the same VIN range
VCM range	0	3.3	<-- Op amp VCM [MIN, MAX] limits
Reference Voltage	3.3		<-- Chose accurate voltage (Cannot use zero)

0 Ron Michallick 9 months ago in reply to Ron Michallick

TI__Guru**** 165626 points

Arvind,

More simple, VOUT = -VIN / 5 ; so -15V in is 3V out

0 Arvind 9 months ago in reply to Ron Michallick

Prodigy 175 points

Hello There,

Thank you for providing the circuit. I do have one concern: can the op-amp handle inputs that go beyond its supply rails? in this case if the input is -15V and at inverting terminal -0.4V (from the simulations), which is less than 0V.

+1 Clemens Ladisch 9 months ago in reply to Arvind

Guru 317480 points

The current flowing through the clamping diode will be limited by R1. Input voltages below GND are outside the guaranteed common-mode range, but this device has no phase reversal, so the amplifier should eventually regulate correctly.

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TLV369: Negative Voltage measurement using ADC