Philips Semiconductors Linear Products
Product specification
Sample-and-hold amplifiers
LF198/LF298/LF398
DESCRIPTION
The LF198/LF298/LF398 are monolithic sample-and-hold circuits
which utilize high-voltage ion-implant JFET 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 6µs to 0.01%. A bipolar
input stage is used to achieve low offset voltage and wide
bandwidth. Input offset adjust is accomplished with a single pin and
does not degrade input offset drift. The wide bandwidth allows the
LF198 to be included inside the feedback loop of 1MHz op amps
without having stability problems. Input impedance of 10
10
Ω
allows
high source impedances to be used without degrading accuracy.
P-channel junction FETs are combined with bipolar devices in the
output amplifier to give droop rates as low as 5mV/min with a 1µF
hold capacitor. The JFETs have much lower noise than MOS
devices used in previous designs and do not exhibit high
temperature instabilities. The overall design guarantees no
feedthrough from input to output in the hold mode even for input
signals equal to the supply voltages.
Logic inputs are fully differential with low input current, allowing
direct connection to TTL, PMOS, and CMOS; differential threshold is
1.4V. The LF198/LF298/LF398 will operate from
±5V
to
±18V
supplies. They are available in 8-pin plastic DIP, 8-pin Cerdip, and
14-pin plastic SO packages.
PIN CONFIGURATIONS
FE, N Packages
1
2
3
4
TOP VIEW
8
7
6
5
V+
OFFSET VOLTAGE
INPUT
V–
LOGIC
LOGIC REFERENCE
C
h
OUTPUT
D
1
Package
INPUT
1
NC
2
V–
3
NC
4
NC
5
NC
6
OUTPUT
7
TOP VIEW
14
V
OS
Adj
13
NC
12
V+
11
LOGIC
10
LOGIC REF
9
8
NC
C
h
FEATURES
•
Operates from
±5V
to
±18V
supplies
•
Less than 10µs acquisition time
•
TTL, PMOS, CMOS compatible logic input
•
0.5mV typical hold step at CH=0.01µF
•
Low input offset
•
0.002% gain accuracy
•
Low output noise in hold mode
•
Input characteristics do not change during hold mode
•
High supply rejection ratio in sample or hold
•
Wide bandwidth
ORDERING INFORMATION
DESCRIPTION
8-Pin Ceramic Dual In-Line Package (CERDIP)
14-Pin Plastic Small Outline (SO) Package
8-Pin Ceramic Dual In-Line Package (CERDIP)
8-Pin Plastic Dual In-Line Package (DIP)
8-Pin Ceramic Dual In-Line Package (CERDIP)
8-Pin Plastic Dual In-Line Package (DIP)
NOTE:
1. SO and non-standard pinouts.
APPLICATION
•
The LF198/LF298/LF398 are ideally suited for a wide variety of
sample-and-hold applications, including data acquisition,
analog-to-digital conversion, synchronous demodulation, and
automatic test setup
TEMPERATURE RANGE
-55°C to +125°C
0 to +70°C
0 to +70°C
0 to +70°C
-25°C to +85°C
-25°C to +85°C
ORDER CODE
LF198FE
LF398D
LF398FE
LF398N
LF298FE
LF298N
DWG #
0580A
0175D
0580A
0404B
0580A
0404B
August 31, 1994
879
853-0135 13721
Philips Semiconductors Linear Products
Product specification
Sample-and-hold amplifiers
LF198/LF298/LF398
FUNCTIONAL DIAGRAM
OFFSET
TYPICAL APPLICATIONS
V+
30k
–
+
3
INPUT
8
LOGIC
LOGIC 7
REFERENCE
6
HOLD
CAPACITOR
300
SAMPLE 5V
HOLD 0V
LOGIC
INPUT
8
7
ANALOG INPUT
3
S/H
5
OUTPUT
1
4
5
6
C
h
OUTPUT
V–
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
S
Supply voltage
Maximum power dissipation
T
A
=25°C (still-air)
3
F package
N package
D package
T
A
Operating ambient temperature range
LF198
LF298
LF398
T
STG
V
IN
Storage temperature range
Input voltage
Logic-to-logic reference differential
voltage
2
Output short-circuit duration
Hold capacitor short-circuit duration
T
SOLD
Lead soldering temperature (10sec max)
-55 to +125
-25 to +85
0 to +70
-65 to +150
Equal to
supply voltage
+7, -30
Indefinite
10
300
sec
°C
V
°C
°C
°C
°C
780
1160
1040
mW
mW
mW
PARAMETER
RATING
±18
UNIT
V
NOTES:
1. The maximum junction temperature of the LF398 is 150°C. When operating at elevated ambient temperature, the packages must be derated
based on the thermal resistance specified.
2. Although the differential voltage may not exceed the limits given, the common-mode voltage on the logic pins must always be at least 2V
below the positive supply and 3V above the negative supply.
3. Derate above 25°C, at the following rates:
F package at 6.2mW/°C
N package at 9.3mW/°C
D package at 8.3mW/°C
August 31, 1994
880
Philips Semiconductors Linear Products
Product specification
Sample-and-hold amplifiers
LF198/LF298/LF398
DC ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following conditions apply: unit is in “sample” mode; V
S
=
±15V;
T
J
= 25°C; -11.5V3 V
IN
≤
+11.5V; C
H
=0.01µF;
and R
L
= 10kΩ. Logic reference voltage = 0V and logic voltage = 2.5V.
SYMBOL
V
OS
I
BIAS
PARAMETER
Input offset voltage
4
Input bias current
4
Input impedance
Gain error
Feedthrough attenuation
ratio at 1kHz
Output impedance
“HOLD“ step
2
I
CC
Supply current
4
Logic and logic reference
input current
Leakage current into hold
capacitor
4
t
AC
Acquisition time to 0.1%
Hold capacitor charging
current
Supply voltage rejection
ratio
Differential logic threshold
TEST CONDITIONS
T
J
=25°C
Full temperature range
T
J
=25°C
Full temperature range
T
J
=25°C
T
J
=25°C,
10
10
0.002
0.005
0.02
86
96
0.5
0.5
4.5
2
30
4
20
5
80
0.8
110
1.4
2.4
80
0.8
2
4
2.0
5.5
10
100
1.0
4.5
2
30
4
20
5
110
1.4
2.4
80
90
0.5
4
6
2.5
6.5
10
200
5
LF198/LF298
Min
Typ
1
Max
3
5
25
75
10
10
0.004
0.01
0.02
10
Min
LF398
Typ
2
Max
7
10
50
100
UNIT
mV
nA
Ω
%
dB
Ω
mV
mA
µA
pA
µs
mA
dB
V
R
L
=10k
Full temperature range
T
J
=25°C, C
h
=0.01µF
T
J
=25°C, “HOLD“ mode
Full temperature range
T
J
=25°C, C
h
=0.01µF, V
OUT
=0
T
J
≤
25°C
T
J
= 25°C
T
J
=25°C, “HOLD“ mode
∆V
OUT
=10V, C
h
=1000pF
C
h
=0.01µF
V
IN
-V
OUT
=2V
V
OUT
=0
T
J
=25°C
NOTES:
1. Unless otherwise specified, the following conditions apply. Unit is in “sample“ mode, V
S
=±15V, T
J
=25°C, -11.5V
≤
V
IN
≤
+11.5V, C
h
= 0.01µF,
and R
L
= 10kΩ. Logic reference voltage = 0V and logic voltage = 2.5V.
2. Hold step is sensitive to stray capacitive coupling between input logic signals and the hold capacitor. 1pF, for instance, will create an
additional 0.5mV step with a 5V logic swing and a 0.01µF hold capacitor. Magnitude of the hold step is inversely proportional to hold
capacitor value.
3. Leakage current is measured at a junction temperature of 25°C. The effects of junction temperature rise due to power dissipation or elevated
ambient can be calculated by doubling the 25°C value for each 11°C increase in chip temperature. Leakage is guaranteed over full input
signal range.
4. The parameters are guaranteed over a supply voltage of
±5
to
±18V.
August 31, 1994
881
Philips Semiconductors Linear Products
Product specification
Sample-and-hold amplifiers
LF198/LF298/LF398
TYPICAL DC PERFORMANCE CHARACTERISTICS
Input Bias Current
25
20
15
CURRENT (mA)
10
5
0
–5
–10
–15
–50
–25
0
25
50
75
100
125 150
CURRENT (mA)
20
18
16
14
12
10
8
6
4
2
0
–50
–25
0
25
50
75
100
125 150
SINKING
SOURCING
Output Short Circuit Current
INPUT VOLTAGE — OUTPUT VOLTAGE (mV)
1
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1
–15
–10
Gain Error
T
J
= 25°C
R
L
= 10k
SAMPLE MODE
–5
0
5
10
15
JUNCTION TEMPERATURE (°C)
JUNCTION TEMPERATURE (°C)
INPUT VOLTAGE (V)
Hold Step
100
V+ = V– = 15V
T
J
= 25°C
10
HOLD STEP (mV)
CURRENT (nA)
10
100
Leakage Current Into
Hold Capacitor
2
V
S
=
±15V
V
OUT
= 0
HOLD MODE
NORMALIZED HOLD STEP AMPLITUDE
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
–25
0
25
50
75
100
125 150
–15
Hold Step Input Voltage
T
J
= 100°C
1
1
T
J
= 25°C
0.1
10
–1
T
J
= 55°C
0.01
100pF
1000pF
0.01µF
0.1µF
1µF
10
–2
–50
–10
–5
0
5
10
15
HOLD CAPACITOR
JUNCTION TEMPERATURE (°C)
INPUT VOLTAGE (V)
TYPICAL AC PERFORMANCE CHARACTERISTICS
Acquisition Time
1
V
IN
= 0 TO
±10V
1%
10
TIME (
µ
s)
T
J
= 25°C
250
V+ = V– = 15V
225
200
TIME (ns)
0.1%
175
150
125
100
75
50
25
1000
0.001
0.01
HOLD CAPACITOR (µF)
0.1
0
–50
–25
0
25
50
POSITIVE
INPUT
STEP
0.1
75 100 125 150
0.1
1
10
100
1
NEGATIVE
INPUT
STEP
∆V
OUT
≤
1mV
∆V
IN
= 10V
Aperture Time
100
Capacitor Hysteresis
10
0.01%
100
JUNCTION TEMPERATURE (°C)
SAMPLE TIME (ms)
August 31, 1994
882
Philips Semiconductors Linear Products
Product specification
Sample-and-hold amplifiers
LF198/LF298/LF398
TYPICAL AC PERFORMANCE CHARACTERISTICS
(Continued)
Dynamic Sampling Error
100
10 0
Output Droop Rate
2
1.8
‘Hold’ Sampling Time
330pF
V+ = V– = 15V
SETTLING TIME
10
∆
V/
∆
T (V/SEC)
ERROR (mV)
330pF
±
1
10–1
TIME (
µ
s)
T
J
=85°C
10–2
T
J
=25°C
10–3
1000pF
10–4
0.1
1
10
100
1000
100pF
1000pF
0.01µF
0.1µF
1µF
INPUT SLEW RATE (V/ms)
HOLD CAPACITOR
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
–10
–100
0
–50 –25
0
25
50
75
100 125
150
JUNCTION TEMPERATURE (°C)
Phase And Gain
(Input to Output, Small-Signal)
5
C
h
= 0
GAIN — INPUT TO OUTPUT (dB)
0
–5
–10
C
h
= 1000pF
C
h
≥
0.01µF
C
h
= 1000pF
C
h
=
0.01µF
80
70
60
50
40
30
20
10
C
h
= 0
0
1k
10k
100k
1M
10M
160
140
REJECTION RATIO (dB)
120
100
80
60
40
20
INPUT TO OUTPUT PHASE DELAY ( o )
Power Supply Rejection
160
T
J
=25°C
V+ = V– = 15V
V
OUT
= 0°C
NOISE (nV/ Hz)
140
120
100
Output Noise
POSITIVE
MODE
NEGATIVE
MODE
‘HOLD’ MODE
80
60
40
20
0
SAMPLE
MODE
C
h
≥
0.01µF
0
100
1k
10k
100k
1M
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
Feedthrough Rejection Ratio
(Hold Mode)
–130
V+ = V– = 15V
–120
–110
RATIO (dB)
C
h
=
0.1µF
–100
–90
–80
C
h
= 1000pF
–70
–60
–50
10
100
100
1k
10k 100k
1M
FREQUENCY (Hz)
C
h
=
0.01µF
T
J
=25°C
V
IN
= 10Vp-p
V
7.8
= 0
August 31, 1994
883
