What is the difference between the packing of OPA657U and OPA657UB? I want to order sample IC first, which one should I order?
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Thanks for the reply.. I want to design a low noise high speed amplifier circuit. For this which ic will be better opa657 or opa659?
1) opa657 has got lesser noise and higher bandwidth but i am not very much clear about the slew rate difference. opa657 has got 700 V/uSec for gain of +10 V/V, while opa659 has got 2550 V/uSec for gain of +1 V/V. Which one out of these will be better for gain of +10 V/V or even more?
2) In case of opa659, bandwidth is defined as 35 MHz for V0 = 200mVpp, G = +10 V/V, does it mean that for higher output voltage (V0), bandwidth will be even lower?
Hi Samir,
opa847 has good noise level and BW but it has quite higher input bias current. Since my application is to detect low current, so i can not go with that.
As you mentioned, that for good stability opa657 should be used for gain > 7V/V. Since we want to use it for higher gains (10V/V) then there should not be any problem regarding stability too. So can we say that opa657 will be better than opa659 for this application? My only worry is about slew rate. Still i don't get how to compare slew rate of these two, which is better for gain >= 10V/V.
If we want to get gain >1000, can we go for two stages of opa657 with gain 40 V/V each?
At high frequency, d.c. power supply also adds noise in the output voltage signal. Can you suggest some IC which can give high stable d.c. power supply (6 V) required for these op-amps?
Dear Samir,
I have used OPA659IDRBT product which has SON(DRB) type packaging and using that I got fabricated a PCB board. Now, I want to use OPA657 on the same PCB replacing OPA659. For that I ordered OPA657UB and OPA657U but they have different packaging type i.e. SOIC(D). Kindly suggest me, which product code I can use for opa657 on the same board.
-- Nishant
Dear Samir,
I have checked that for higher gain (>10) opa657 has fast responce time (rise and fall time) as compare to opa659. I want to measure a low voltage signal (< 50 micro volt). So i want to design an amplifier for that which can respond very fast (< 1 ns). Kindly suggest me.
Dear Samir,
I have seen in opa659, that although i apply 6V at Vcc, opamp saturates at 4 V. Is there any specific reason behind this?
For opa657, i can see that there are two operating ranges in terms of output voltage i. e 200mVpp and 2Vpp. So what is the safe range of output voltage so as to avoid saturation of the opamp?
The OPA659 has an output swing limitation of 2V from the positive rail when driving a 100Ohm load. Please see Page 4 of the datasheet for this spec. Amplifiers usually have some kind of limitation like this. Even amplifiers classified as rail-to-rail may only swing to within 200mV of the rail in some cases. As the output load increases it is more difficult to get close to the rails.
The OPA657 specifications are on page 3 of the datasheet. It is 1.5V from the rail on the output side under 100Ohm load. There will also be an input swing limitation (under "Input" characteristics of the electrical table) that may be important depending on the amplifier configuration.
Please also look at the following training to better understand amplifier specifications and how they work. You may find this quite useful as a refresher.
-Samir
In opa659, decoupling capacitors connected with Vcc are parallel combination of 0.1uF and 10uF while for opa657, it is 0.1uF and 6.8uF. Why? How to decide these values?