Dear Specialists
My customer has a question for LMH6612.
Could you please let me know.
He wants to know about the phenomenon at overload.
When the input voltage is higher, the output is satulated.
(For example the gain is 10, it is easy to satulate.)
(1)If the output is satulated, how does the amplifier work?
For instance, only THD increase or polality change or another.
(2)How long is the overload recovery?
It is not described at datasheet.
Best regards,
Hello Shinichi-san,
I have measured the LMH6611 / LMH6612 output overload recovery time that we've been discussing.
|
Condition |
Baseline Prop. Delay (ns) |
Measured input / output zero-crossing Delta (ns) |
Overload Recovery Time (ns) |
|
Pos. to Neg. transition (Vout railed at Vcc) |
16 |
18 |
2 (=18-16) |
|
Neg. to Pos. transition (Vout railed at Vee) |
16 |
26 |
10 (=26-16) |
Here is the measured overloaded recovery waveform for your reference (there is a baseline 16ns zero-crossing delta between input and output which needs to be subtracted out):
In addition, I've also measured the LMH6611 / LMH6612 supply current / channel (I+ from Vcc, and I- from Vee) when the output is railed against Vcc or Vee, for your review:
|
Condition |
Both Channels Supply Current Measured (only one channel saturated!) |
|
|
I+ (mA) |
I- (mA) |
|
|
No Signal |
7 |
7 |
|
Saturated towards V+ |
16 |
13 |
|
Saturated towards V- |
12 |
14 |
|
Supply current / channel in V+ saturation |
12.5 (=16-7/2) |
9.5 (=13-7/2) |
|
Supply current / channel in V- saturation |
8.5 (=12-7/2) |
10.5 (=14-7/2) |
Regards,
Hooman
Hello Shinichi-san,
I've measured the LMH6612 (LMH6611) overload recovery time over temperature (HOT= 95C, COLD= -45C) and I hardly see any change from room temperature and for all conditions read less than 10ns! So, this is pretty good news.
|
Condition |
Baseline Prop. Delay (ns) |
Measured input / output zero-crossing Delta (ns) |
Overload Recovery Time (ns) |
|
Pos. to Neg. transition (Vout railed at Vcc) HOT |
14 |
18 |
4 (=18-14) |
|
Neg. to Pos. transition (Vout railed at Vee) HOT |
16 |
24 |
8 (=24-16) |
|
Condition |
Baseline Prop. Delay (ns) |
Measured input / output zero-crossing Delta (ns) |
Overload Recovery Time (ns) |
|
Pos. to Neg. transition (Vout railed at Vcc) COLD |
14 |
20 |
6 (=20-14) |
|
Neg. to Pos. transition (Vout railed at Vee) COLD |
16 |
24 |
8 (=24-16) |
Here is the data if you like to see the plots:
HOT:
COLD:
Regards,
Hooman
Hi Shinichi,
1. Overdrive recovery: I can capture waveforms of the LMH6612 output banging against V+ and V- and how it recovers, as you have shown in your PowerPoint, by next week. However, I will leave it to you to interpret the recovery time from that, because to me, I'm not sure how you would read recovery time off the waveform you are asking for!
Here is the OPA857 that you have noted is specified (and I'm not sure if Figure 13 is showing the same thing or not?
OPA857 Recovery:
2. THD with Av=-10V/V, Vs= 3.3V at various output swings (RL= 1kohm): I don't expect much variation up to 2Vpp output swing, from Vs=5V to Vs=3.3V as the distortion data in the Electrical tables shows very little variation:
There will be some distortion increase with Av= -10V/V relative to Av= 2V/V or Av= -1V/V (these two last gains would be very similar to each other from the loop gain point of view and most likely distortion).
I don't have the exact data you are looking for right now. I've asked around to see if we have some information to share or not? If I cannot get this information, I'd have to defer it to your own / customer evaluation instead as my work load would not allow me to take this data immediately. Sorry about that.
3. Input Bias Current Drift over temperature: Unfortunately, apart from Figure 41 shown below, more data is not available!
What you can deduce from Figure 41, for a typical device, is that worst case IB (I_bias) is most likely at cold temperature. Current is always negative (meaning out of the LMH6612 input pins.
The input bias current is guaranteed to be less than -11.1uA over temperature, but I don't have any additional data to say how it varies with temperature on individual devices:
Regards,
Hooman
Hello Shinichi,
Regarding the LMH6612 waveform after banging into the rails:
1. Overdrive Recovery:
The plots I sent you earlier already show these waveforms. I've taken the previous plots (HOT temperature in this case) and zoomed in on these regions below. Room temp and COLD look very similar.
Rising:
Falling:
2. THD with Av=-10V/V, Vs= 3.3V at various output swings (RL= 1kohm):
Unfortunately I could not locate any useful data to share and you may have to do the testing yourself. You generally expect higher closed loop gain and lower supply voltages to affect distortion negatively (worsens), but I'm not sure I could put a number on it.
Regards,
Hooman
