LF198-N: 5962-8760801GA(LF198H/883)

Hi Kim,

Wantae Kim said:

1. In datasheet of LF198, there is a graph about Output Droop Rate(See below) which has 2 lines of 25ºC and 85ºC.

I hope to get data lines between 25ºC and 85ºC, so do data lines have linearity characteristic by temperature?

The droop rate is a measure of how quickly the charge losses occur. It is specified in delta mV per second (mV/s) and indicates the rate of change of the stored voltage over time.

I think that the plot likely refers to droop rate for polypropylene or polystyrene capacitor that is used for the temperature characterization with LF198 IC. It behaves linearly only in the small ΔmV/sec in the ultra low dielectric absorption capacitors. 

Wantae Kim said:

2. Coud you give me Max +Icc/-Icc(Supply current) data with +15V / -15V / RL(Load) = Infinity ohm condition?

The datasheet indicated from the supply current range is typically 4.5mA, no greater than 5.5mA, if RL = 10kΩ between ±5Vdc to ±18Vdc, if the LF198 is operating in a linear region. what is your infinity ohm condition mean? Please clarify. 

If you have other questions, please let me know. 

Best,

Raymond

Dear Zhang,

Thank you for your fast reply.

1. You mean that if there is dielectric absorption capacitor as a hold capacitor, it works linearly like plot in datasheet.

Am I right?

2. In my schematic, sample & Hold output is connected with voltage follower input. As you know, Amplifier input has ideally infinite impedence, so I described "Infinity ohm".

Hi Kim,

Wantae Kim said:

You mean that if there is dielectric absorption capacitor as a hold capacitor, it works linearly like plot in datasheet.

yes, the plot is likely referenced to specific polypropylene or polystyrene capacitors (not any other capacitors). The datasheet was initially published in early 2000's and it should be based on the lab results. Keep in mind that both axis are log scales, and the ΔV/sec is from Δ1mV to Δ1V, and temperature refers to Tj, or junction temperature inside of IC (this is not exactly as Tamb temperature), where the load is 10kΩ. If the load is very large, say in GΩ range, then Tamb = Tj approximately. 

Wantae Kim said:

2. In my schematic, sample & Hold output is connected with voltage follower input. As you know, Amplifier input has ideally infinite impedence, so I described "Infinity ohm".

Since your there is no load in your application, Tamb = Tj and it will determine the curve. It Tamb = 25C, then Tj = 25C in Figure 4 may be more representative, which the droop rate in ΔV/sec is from Δ300mV/sec to Δ0.1mV/sec from 100pF to 0.4uF hold capacitor or the large the holding capacitor, lower the droop rate at output  per Figure 4 plot. 

If you have other questions, please let me know. 

Best,

Raymond