# Wrongly documented TI LM324 unity-gain bandwidth?

They specify a generic GBW of 1.2MHz. This is usually done with no output applied, from what I understand. Then there is the $$\ A_{vd} \$$ which is max 100K (100 V/mV). This is the open-loop gain measured with a load, so taking into account loading effects, if I get it right.

Is this gain really reducing by a factor of 10 with few $$\ k \Omega \$$ on the output?

To understand this better, I read the SLOA11 from TI. They mention $$\ B_1 \$$ to be the bandwidth at unity-gain with a load specified under the $$\ A_{vd} \$$ measurement, which should result in a BW of 100kHz. Making it different from the GBP measurement with no load (resulting in unity BW of 1.2 MHz). But in the LM324 datasheet, $$\ B_1 = 1.2MHz\$$ instead of $$\ 100kHz \$$. So I am not sure here what are the correct terms and how to use them.

• "A few $k\Omega$" equates to a few mA, which definitely hinders the performance of a decades-old low-power op-amp. – DSWG Oct 25 '18 at 22:18
• Do you dimensional analysis. 1.2MHz / 100K does not equal 12 -- it equals 12Hz. GBW is gain bandwidth product. In theory a vendor could try to pass off a device with a gain of 100 and a 3db frequency of 1MHz as an op-amp with a GBW of 100MHz (and, in fact, I recall seeing a data sheet for one about 20 years ago -- so maybe it's not just theory!) – TimWescott Oct 25 '18 at 23:14