Output impedance problem of parallel reference voltage

xiaxingxing

Output impedance problem of parallel reference voltage [Copy link]

Regarding the output impedance of the shunt-type reference voltage, I have the following two questions to ask you:

1. What is the output impedance of the shunt voltage reference REF3025? See the attached specification.

2. The picture is a curve chart in the REF3025 specification book. What does this picture mean? Thank you

maychang

This is in the manual.

Didn't read the manual carefully enough.

maychang

"The picture is a curve chart in the REF3025 specification book. What does this picture mean? Thank you."

The text below the curve makes it very clear: Output Impedance vs Frequemcy , output impedance versus frequency.

The vertical axis is a logarithmic scale.

Jack315

This is the frequency dependent impedance.

At low frequencies, it is about resistive, and the decibel number is very small, close to zero, so it is a few ohms.

At 20 dB (40KHz~50KHz), the impedance is about 10 ohms:

The load of REF3025 is estimated to be approximately 100 ohms based on the recommended operating conditions (2.5V, 25mA).

Normal applications should be fine.

If it is a DC-DC power supply, the ripple frequency is roughly 40KHz~50KHz.

At this time, the increased impedance may affect the circuit performance (accuracy).

xiaxingxing

Jack315 posted on 2022-1-22 17:17 This is the impedance related to the frequency. At the low frequency end, it is about resistive. The decibel number is very small, close to zero, so it is a few ohms. At 20 ...

Hello, does the frequency on the horizontal axis refer to the noise frequency in the input voltage? Thank you!

xiaxingxing

Jack315 posted on 2022-1-22 17:17 This is the impedance related to the frequency. At the low frequency end, it is about resistive. The decibel number is very small, close to zero, so it is a few ohms. At 20 ...

Hi, I have another question for you.

The first picture below is a screenshot of the specs for TL431, which shows that its output impedance is 0.2 ohm (TYP).

My question is, if I use TL431 to connect the circuit shown in the second figure below, is the output impedance still 0.2 ohm? Why not R (=1k ohm)? Thank you!

maychang

xiaxingxing posted on 2022-1-22 23:46 Hello, I have another question for you. The first picture below is a screenshot of the spec of TL431, which shows that its output impedance is 0.2 ohm (TYP). ...

If the TL431 is removed (open circuit) in the figure on the 6th floor, the output impedance is about 1 kilo-ohm. The reason is: the input is a voltage source, the internal resistance is approximately zero, and a 1 kilo-ohm resistor is connected in series, the output impedance is approximately 1 kilo-ohm.

After adding TL431, TL431 itself is a voltage source with an internal resistance of about 0.2 ohms (approximately zero) and no series resistance, so the output impedance is 0.2 ohms.

maychang

xiaxingxing posted on 2022-1-22 23:46 Hello, I have another question for you. The first picture below is a screenshot of the spec of TL431, which shows that its output impedance is 0.2 ohm (TYP). ...

The TL431 in the figure on the 6th floor is roughly equivalent to a battery. The voltage across the two ends of an ordinary dry cell is 1.5V (varies with the age of the battery and the temperature), and the internal resistance is roughly 0.1 ohm to 1 ohm. We can say that the output impedance of this dry cell is 0.1 ohm to 1 ohm.

maychang

xiaxingxing posted on 2022-1-22 23:46 Hello, I have another question for you. The first picture below is a screenshot of the spec of TL431, which shows that its output impedance is 0.2 ohm (TYP). ...

If a dry cell battery is connected in series with a 1 kilo-ohm resistor and then connected to a load, the output impedance of the dry cell battery (plus the resistor) is 1 kilo-ohm.

xiaxingxing

maychang posted on 2022-1-23 14:49 If a dry cell is connected in series with a 1 kilo-ohm resistor and then connected to a load, the output impedance of the dry cell (plus the resistor) is 1 kilo-ohm.

OK, I understand. Thank you for the detailed answer.