1994f.indd
LT1994
1
1994f
Low Noise, Low Distortion
Fully Differential Input/
Output Amplifi er/Driver
The LT
1994 is a high precision, very low noise, low distor-
tion, fully differential input/output amplifi er optimized for
3V, single supply operation. The LT1994's output common
mode voltage is independent of the input common mode
voltage, and is adjustable by applying a voltage on the
V
OCM
pin. A separate internal common mode feedback
path provides accurate output phase balancing and reduced
even-order harmonics. This makes the LT1994 ideal for
level shifting ground referenced signals for driving dif-
ferential input, single supply ADCs.
The LT1994 output can swing rail-to-rail and is capable
of sourcing and sinking up to 85mA. In addition to the
low distortion characteristics, the LT1994 has a low input
referred voltage noise of 3nV/Hz. This part maintains
its performance for supply voltages as low as 2.375V. It
draws only 13.5mA of supply current and has a hardware
shutdown feature that reduces current consumption to
300A.
The LT1994 is available in an 8-pin MSOP or 8-pin DFN
package.
Differential Input A/D Converter Driver
Single-Ended to Differential Conversion
Differential Amplifi cation with Common Mode
Translation
Rail-to-Rail Differential Line Driver/Receiver
Low Voltage, Low Noise, Differential Signal
Processing
Fully Differential Input and Output
Wide Supply Range: 2.375V to 12.6V
Rail-to-Rail Output Swing
Low Noise: 3nV/Hz
Low Distortion, 2V
P-P
, 1MHz: 94dBc
Adjustable Output Common Mode Voltage
Unity Gain Stable
Gain-Bandwidth: 70MHz
Slew Rate: 65V/s
Large Output Current: 85mA
DC Voltage Offset <2mV MAX
Open-Loop Gain: 100V/mV
Low Power Shutdown
8-Pin MSOP or 3mm
3mm DFN Package
A/D Preamplifi er: Single-Ended Input to Differential Output with Common
Mode Level Shifting
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
1994 TA01
24.9
3V
0.1
F
24.9
47pF
499
499
499
499
3V
10
F
10
F
0.1
F
V
IN
2V
P-P
V
OCM
= 1.5V
GND
V
DD
A
IN
A
IN
+
V
REF
CONV
SD0
SCK
50.4MHz
LTC1403A-1
+
+
LT1994
V
OCM
LT1994 Driving an LTC1403A-1 1MHz
Sine Wave, 8192 Point FFT Plot
FREQUENCY
(MHz)
0
120
110
100
90
80
70
60
50
40
30
20
10
DIFFERENTIAL
OUTPUT MAGNITUDE (dB)
0
0.35
0.70
1994 TA01b
1.40
1.05
F
SAMPLE
= 2.8Msps
F
IN
= 1.001MHz
INPUT = 2V
P-P
,
SINGLE ENDED
SFDR = 93dB
LT1994
2
1994f
TOP VIEW
DD PACKAGE
8-LEAD (3mm
3mm) PLASTIC DFN
5
6
7
8
4
3
2
1
IN
V
OCM
V
+
OUT
+
IN
+
SHDN
V
OUT
T
JMAX
= 125C,
JA
= 160C/W
UNDERSIDE METAL CONNECTED TO V
1
2
3
4
IN
V
OCM
V
+
OUT
+
8
7
6
5
IN
+
SHDN
V
OUT
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150C,
JA
= 140C/W
ORDER PART NUMBER
DD PART MARKING*
ORDER PART NUMBER
MS8 PART MARKING*
LT1994CDD
LT1994IDD
LBQM
LBQM
LT1994CMS8
LT1994IMS8
LTBQN
LTBQN
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
*The temperature grade is identifi ed by a label on the shipping container. Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OSDIFF
Differential Offset Voltage
(Input Referred)
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
2
2
2
3
mV
V
OSDIFF
/ T
Differential Offset Voltage Drift
(Input Referred)
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
3
3
3
3
V/C
I
B
Input Bias Current
(Note 6)
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
45
45
45
45
18
18
18
18
3
3
3
3
A
Total Supply Voltage (V
+
to V
) ..............................12.6V
Input Voltage (Note 2) ............................................... V
S
Input Current (Note 2) ..........................................10mA
V
OCM
, SHDN ............................................................. V
S
Output Short-Circuit Duration (Note 3) ............ Indefi nite
Operating Temperature Range (Note 4) ... 40C to 85C
Specifi ed Temperature Range (Note 5) .... 40C to 85C
(Note 1)
ELECTRICAL CHARACTERISTICS
ABSOLUTE AXI U
RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
Junction Temperature
MS8 .................................................................. 150C
DFN8 ................................................................. 125C
Storage Temperature Range
MS8 ................................................... 65C to 150C
DFN8 .................................................. 65C to 125C
Lead Temperature (Soldering, 10 sec) .................. 300C
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. V
+
= 3V, V
= 0V, V
CM
= V
OCM
= V
ICM
= mid-supply, V
SHDNBAR
= OPEN, R
I
= R
F
= 499 , R
L
= 800 to a mid-supply voltage (See Figure 1) unless otherwise noted. V
S
is defi ned (V
+
V
). V
OUTCM
is defi ned as
(V
OUT
+
+ V
OUT
)/2. V
ICM
is defi ned as (V
IN
+
+ V
IN
)/2. V
OUTDIFF
is defi ned as (V
OUT
+
V
OUT
). V
INDIFF
is defi ned as (V
IN
+
V
IN
).
LT1994
3
1994f
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. V
+
= 3V, V
= 0V, V
CM
= V
OCM
= V
ICM
= mid-supply, V
SHDNBAR
= OPEN, R
I
= R
F
= 499 , R
L
= 800 to a mid-supply voltage (See Figure 1) unless otherwise noted. V
S
is defi ned (V
+
V
). V
OUTCM
is defi ned as
(V
OUT
+
+ V
OUT
)/2. V
ICM
is defi ned as (V
IN
+
+ V
IN
)/2. V
OUTDIFF
is defi ned as (V
OUT
+
V
OUT
). V
INDIFF
is defi ned as (V
IN
+
V
IN
).
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
OS
Input Offset Current
(Note 6)
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
0.2
0.2
0.2
0.2
2
2
3
4
A
R
IN
Input Resistance
Common Mode
Differential Mode
700
4.5
k
k
C
IN
Input Capacitance
Differential
2
pF
e
n
Differential Input Referred Noise Voltage
Density
f = 50kHz
3
nV/Hz
i
n
Input Noise Current Density
f = 50kHz
2.5
pA/Hz
e
nVOCM
Input Referred Common Mode Output
Noise Voltage Density
f = 50kHz, V
OCM
Shorted to Ground
15
nV/Hz
V
ICMR
(Note 7)
Input Signal Common Mode Range
V
S
= 3V
V
S
= 5V
0
5
1.75
3.75
V
CMRRI
(Note 8)
Input Common Mode Rejection Ratio
(Input Referred) V
ICM
/ V
OSDIFF
V
S
= 3V, V
ICM
= 0.75V
55
85
dB
CMRRIO
(Note 8)
Output Common Mode Rejection Ratio
(Input Referred) V
OCM
/ V
OSDIFF
V
S
= 5V, V
OCM
= 2V
65
85
dB
PSRR
(Note 9)
Differential Power Supply Rejection
( V
S
/ V
OSDIFF
)
V
S
= 3V to 5V
69
105
dB
PSRRCM
(Note 9)
Output Common Mode Power Supply
Rejection ( V
S
/ V
OSOCM
)
V
S
= 3V to 5V
45
70
dB
G
CM
Common Mode Gain (V
OUTCM
/ V
OCM
)
V
S
= 2.5V
1
V/V
Common Mode Gain Error
100 (G
CM
1)
V
S
= 2.5V
0.15
1
%
BAL
Output Balance ( V
OUTCM
/ V
OUTDIFF
)
V
OUTDIFF
= 2V
Single-Ended Input
Differential Input
65
71
46
50
dB
dB
V
OSCM
Common Mode Offset Voltage
(V
OUTCM
V
OCM
)
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
2.5
2.5
2.5
2.5
25
25
30
40
mV
mV
mV
mV
V
OSCM
/ T
Common Mode Offset Voltage Drift
V
S
= 2.375V, V
ICM
= V
S
/4
V
S
= 3V
V
S
= 5V
V
S
= 5V
5
5
5
5
V/C
V/C
V/C
V/C
V
OUTCMR
(Note 7)
Output Signal Common Mode Range
(Voltage Range for the V
OCM
Pin)
V
S
= 3V, 5V
V
+ 1.1
V
+
0.8
V
R
INVOCM
Input Resistance, V
OCM
Pin
30
40
60
k
V
MID
Voltage at the V
OCM
Pin
V
S
= 5V
2.45
2.5
2.55
V
V
OUT
Output Voltage, High, Either Output Pin
(Note 10)
V
S
= 3V, No Load
V
S
= 3V, R
L
= 800
V
S
= 3V, R
L
= 100
70
90
200
140
175
400
mV
mV
mV
V
S
= 5V, No Load
V
S
= 5V, R
L
= 800
V
S
= 5V, R
L
= 100
150
200
900
325
450
2400
mV
mV
mV
ELECTRICAL CHARACTERISTICS
LT1994
4
1994f
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Voltage, Low, Either Output Pin
(Note 10)
V
S
= 3V, No Load
V
S
= 3V, R
L
= 800
V
S
= 3V, R
L
= 100
30
50
125
70
90
250
mV
mV
mV
V
S
= 5V, No Load
V
S
= 5V, R
L
= 800
V
S
= 5V, R
L
= 100
80
125
900
180
250
2400
mV
mV
mV
I
SC
Output Short-Circuit Current, Either
Output Pin (Note 11)
V
S
= 2.375V, R
L
= 10
V
S
= 3V, R
L
= 10
V
S
= 5V, R
L
= 10
V
S
= 5V, V
CM
= 0V, R
L
= 10
25
30
40
45
35
40
65
85
mA
mA
mA
mA
SR
Slew Rate
V
S
= 5V
V
S
= 5V, V
CM
= 0V
50
50
65
65
85
85
V/S
GBW
Gain-Bandwidth Product
(f
TEST
= 1MHz)
V
S
= 3V, T
A
= 25C
V
S
= 5V, V
CM
= 0V, T
A
= 25C
58
58
70
70
MHz
Distortion
V
S
= 3V, R
L
= 800 , f
IN
= 1MHz,
V
OUT
+
V
OUT
= 2V
P-P
Differential Input
2nd
Harmonic
3rd
Harmonic
Single-Ended Input
2nd
Harmonic
3rd
Harmonic
99
96
94
108
dBc
dBc
dBc
dBc
t
S
Settling Time
V
S
= 3V, 0.01%, 2V Step
V
S
= 3V, 0.1%, 2V Step
120
90
ns
ns
A
VOL
Large-Signal Voltage Gain
V
S
= 3V
100
dB
V
S
Supply Voltage Range
2.375
12.6
V
I
S
Supply Current
V
S
= 3V
V
S
= 5V
V
S
= 5V
13.3
13.9
14.8
18.5
19.5
20.5
mA
mA
mA
I
SHDN
Supply Current in Shutdown
V
S
= 3V
V
S
= 5V
V
S
= 5V
0.225
0.375
0.7
0.8
1.75
2.5
mA
mA
mA
V
IL
SHDN Input Logic Low
V
S
= 2.375V to 5V
V
+
2.1
V
V
IH
SHDN Input Logic High
V
S
= 2.375V to 5V
V
+
0.6
V
R
SHDN
SHDN Pull-Up Resistor
V
S
= 2.375V to 5V
40
55
75
k
t
ON
Turn-On Time
V
SHDN
0.5V to 3V
1
s
t
OFF
Turn-Off Time
V
SHDN
3V to 0.5V
1
s
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The inputs are protected by a pair of back-to-back diodes. If the
differential input voltage exceeds 1V, the input current should be limited to
less than 10mA.
Note 3: A heat sink may be required to keep the junction temperature
below the absolute maximum rating when the output is shorted
indefi nitely.
Note 4: The LT1994C/LT1994I are guaranteed functional over the operating
temperature range 40C to 85C.
ELECTRICAL CHARACTERISTICS
Note 5: The LT1994C is guaranteed to meet specifi ed performance from
0C to 70C. The LT1994C is designed, characterized, and expected to
meet specifi ed performance from 40C to 85C but is not tested or
QA sampled at these temperatures. The LT1994I is guaranteed to meet
specifi ed performance from 40C to 85C.
Note 6: Input bias current is defi ned as the average of the input currents
fl owing into Pin 1 and Pin 8 (IN
and IN
+
). Input Offset current is defi ned
as the difference of the input currents fl owing into Pin 8 and Pin 1
(I
OS
= I
B
+
I
B
).
The
denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25C. V
+
= 3V, V
= 0V, V
CM
= V
OCM
= V
ICM
= mid-supply, V
SHDNBAR
= OPEN, R
I
= R
F
= 499 , R
L
= 800 to a mid-supply voltage (See Figure 1) unless otherwise noted. V
S
is defi ned (V
+
V
). V
OUTCM
is defi ned as
(V
OUT
+
+ V
OUT
)/2. V
ICM
is defi ned as (V
IN
+
+ V
IN
)/2. V
OUTDIFF
is defi ned as (V
OUT
+
V
OUT
). V
INDIFF
is defi ned as (V
IN
+
V
IN
).
LT1994
5
1994f
FREQUENCY (MHz)
0.1
GAIN (dB)
2
1
0
1
2
1
10
100
1994 G06
R
F
= R
I
= 499
5pF FROM EACH
OUTPUT TO GROUND
25pF FROM EACH
OUTPUT TO GROUND
V
S
= 2.5V
V
S
= 3V
FREQUENCY (MHz)
0.1
GAIN (dB)
2
1
0
1
2
1
10
100
1994 G05
R
F
= R
I
= 499
V
S
= 2.5V
V
S
= 5V
V
S
=
5V
V
S
= 3V
TEMPERATURE
(
C)
50
30
INPUT BIAS CURRENT
(
A)
25
20
15
10
25
0
25
50
1994 G03
1.0
INPUT OFFSET CURRENT
(
A)
0.5
0
0.5
1.0
75
100
I
OS
, V
S
= 3V
I
B
, V
S
= 3V
I
B
, V
S
=
5V
I
OS
, V
S
=
5V
TEMPERATURE
(
C)
50
750
DIFFERENTIAL
V
OS
(
V)
500
250
0
250
500
25
0
25
50
1994 G01
75
100
V
S
= 3V
V
CM
= 1.5V
V
OCM
= 1.5V
FOUR TYPICAL UNITS
TEMPERATURE
(
C)
50
2.5
COMMON MODE VOLTAGE
OFFSET (mV)
0
2.5
5.0
7.5
25
0
25
50
1994 G02
75
100
V
S
= 3V
V
CM
= 1.5V
V
OCM
= 1.5V
FOUR TYPICAL UNITS
Differential Input Referred
Voltage Offset vs Temperature
Common Mode Voltage Offset vs
Temperature
Input Bias Current and Input
Offset Current vs Temperature
Gain Bandwidth vs Temperature
Frequency Response vs
Supply Voltage
Frequency Response vs
Load Capacitance
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Note 7: Input Common Mode Range is tested using the Test Circuit of
Figure 1 (R
F
= R
I
) by applying a single ended 2V
P-P
, 1kHz signal to V
INP
(V
INM
= 0), and measuring the output distortion (THD) at the common
mode Voltage Range limits listed in the Electrical Characteristics table,
and confi rming the output THD is better than 40dBc. The voltage range
for the output common mode range (Pin 2) is tested using the Test Circuit
of Figure 1 (R
F
= R
I
) by applying a 0.5V peak, 1kHz signal to the V
OCM
Pin 2 (with V
INP
= V
INM
= 0) and measuring the output distortion (THD)
at V
OUTCM
with V
OCM
biased 0.5V from the V
OCM
pin range limits listed in
the Electrical Characteristics Table, and confi rming the THD is better than
40dB.
Note 8: Input CMRR is defi ned as the ratio of the change in the input
common mode voltage at the pins IN
+
or IN
to the change in differential
input referred voltage offset. Output CMRR is defi ned as the ratio of the
change in the voltage at the V
OCM
pin to the change in differential input
referred voltage offset.
Note 9: Differential Power Supply Rejection (PSRR) is defi ned as the ratio
of the change in supply voltage to the change in differential input referred
voltage offset. Common Mode Power Supply Rejection (PSRRCM) is
defi ned as the ratio of the change in supply voltage to the change in the
common mode offset, V
OUTCM
V
OCM
.
Note 10: Output swings are measured as differences between the output
and the respective power supply rail.
Note 11: Extended operation with the output shorted may cause junction
temperatures to exceed the 150C limit for the MSOP package (or 125C
for the DD package) and is not recommended.
ELECTRICAL CHARACTERISTICS
TEMPERATURE
(
C)
50
66
GAIN BANDWIDTH
(MHz)
72
71
70
69
68
67
25
0
25
50
1994 G04
75
100
V
S
= 3V
V
S
=
5V
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