LF398A

If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales  ffice/Distributors for availability and specifications.
Supply Voltage                                                              ±18V
Power Dissipation (Package
Limitation) (Note 2)                                                    500 mW
Operating Ambient Temperature Range
LF198/LF198A                                               −55˚C to +125˚C
LF298                                                              −25˚C to +85˚C
LF398/LF398A                                                      0˚C to +70˚C
Hold Capacitor Short
Circuit Duration                                                              10 sec
Lead Temperature (Note 4)
H package (Soldering, 10 sec.)                                       260˚C
N package (Soldering, 10 sec.)                                       260˚C
M package:
Vapor Phase (60 sec.)                                                     215˚C
Infrared (15 sec.)                                                             220˚C
Thermal Resistance (JA) (typicals)
H package 215˚C/W (Board mount in still air)
85˚C/W (Board mount in
400LF/min air flow)
N package                                                                    115˚C/W
M package                                                                   106˚C/W    
JC (H package, typical)                                                 20˚C/W
Storage Temperature Range                           −65˚C to +150˚C
Input Voltage                                        Equal to Supply Voltage
Logic To Logic Reference
Differential Voltage (Note 3)                                      +7V, −30V
Output Short Circuit Duration                                      Indefinite

The LF198/LF298/LF398A are monolithic sample-and-hold circuits which utilize BI-FET technology to obtain ultra-high dc accuracy with fast acquisition of signal and low droop rate. Operating as a unity gain follower, dc gain accuracy is 0.002% typical and acquisition time is as low as 6 µs to 0.01%. A bipolar input stage is used to achieve low offset voltage and wide bandwidth. Input offset adjust is accom- plished with a single pin, and does not degrade input offset drift. The wide bandwidth allows the LF198 to be included in- side the feedback loop of 1 MHz op amps without having sta- bility problems. Input impedance of 1010 Ω allows high source impedances to be used without degrading accuracy.

P-channel junction FET's are combined with bipolar devices in the output amplifier to give droop rates as low as 5 mV/min witha1µF hold capacitor. The JFET's have much lower noise than MOS devices used in previous designs and do not exhibit high temperature instabilities. The overall design guarantees no feed-through from input to output in the hold mode, even for input signals equal to the supply voltages.

Logic inputs on the LF398Aare fully differential with low input current, allowing direct connection to TTL, PMOS, and CMOS. Differential threshold is 1.4V. The LF398A will operate from ±5V to ±18V supplies.

An "A" version is available with tightened electrical specifications.