LT1189CS8#TR Linear Technology, LT1189CS8#TR Datasheet - Page 8

• Manufacturer Part Number: LT1189CS8#TR
• Description: IC AMP VID DIFF CURR FDBK 8SOIC
• Manufacturer: Linear Technology

Specifications of LT1189CS8#TR

• Applications: Differential
• Number Of Circuits: 1
• -3db Bandwidth: 35MHz
• Slew Rate: 220 V/µs
• Current - Supply: 13mA
• Current - Output / Channel: 20mA
• Voltage - Supply, Single/dual (±): 4.75 V ~ 16 V, ±2.38 V ~ 8 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A
LT1189
The primary use of the LT1189 is in converting high speed
differential signals to a single-ended output. The LT1189
video difference amplifier has two uncommitted high input
impedance (+) and (–) inputs. The amplifier has another
set of inputs which can be used for reference and feed-
back. Additionally, this set of inputs give gain adjust, and
DC control to the differential amplifier. The voltage gain of
the LT1189 is set like a conventional operational amplifier.
Feedback is applied to pin 8, and it is optimized for gains
of 10 or greater. The amplifier can be operated single-
ended by connecting either the (+) or (–) inputs to the
+/REF (pin 1). The voltage gain is set by the resistors:
(R
Like the single-ended case, the differential voltage gain is
set by the external resistors: (R
input differential signal for which the output will respond
is approximately 170mV.
V
8
IN DIFF
V
PPLICATI
IN
FB
V
IN
+ R
3
2
1
8
3
2
1
8
R
R
G
G
G
–/FB
–/FB
+
–
+/REF
+
–
+/REF
S/D
S/D
)/R
LT1189
LT1189
V
5
5
A
O
V
V
V
R
V
V
R
G
= (V
+
–
FB
= +
FB
+
–
7
4
7
4
.
IN DIFF
R
O
FB
R
+
6
G
6
U
R
+ V
G
IN
S
V
V
)
OUT
OUT
R
FB
I FOR ATIO
R
V
+
U
G
IN
R
G
FB
V
R
IN DIFF
G
V
V
+ R
O
IN
=
(
G
W
R
)/R
3
2
1
8
R
FB
3
2
1
8
G
R
+
+
–
–/FB
+/REF
G
+
–
S/D
+/REF
–/FB
R
S/D
G
LT1189
G
LT1189
5
. The maximum
A
5
(
V
V
V
V
R
R
V
V
= –
IN DIFF
+
–
FB
7
4
FB
+
–
7
4
R
FB
U
R
–
+
G
( (
6
R
R
6
R
LT1189 • AI01
G
FB
G
V
V
V
OUT
IN
OUT
Power Supply Bypassing
The LT1189 is quite tolerant of power supply bypassing.
In some applications a 0.1 F ceramic disc capacitor
placed 1/2 inch from the amplifier is all that is required. In
applications requiring good settling time, it is important to
use multiple bypass capacitors. A 0.1 F ceramic disc in
parallel with a 4.7 F tantalum is recommended.
Calculating the Output Offset Voltage
Both input stages contribute to the output offset voltage at
pin 6. The feedback correction forces balance in the input
stages by introducing an Input V
expression for the output offset voltage is:
V
R
and R
DC reference voltage, for V
I
simplifies to:
V
If R
contributes only 2mV since I
OS
OUT
OUT
S
3
represents the input source resistance, typically 75 ,
R
is normally a small contributor and the expression
FB
+
S
= (V
= V
REF
is limited to 1k, the last term of the equation
2
OS
OS
R
Figure 1. Simplified Input Stage Schematic
–
S
represents finite source impedance from the
(R
+ I
Q1
345 A
OS
FB
300
R
(R
E
+ R
Q2
S
) + I
G
)/R
B
+
(R
G
1 REF
+ I
REF
REF
R
REF
B
B
)) (R
(R
is less than 2 A.
grounded, R
Q3
OS
FB
350 A
300
)
R
at pin 8. The complete
E
FB
Q4
+ R
G
7 V
4 V
)/R
REF
8
+
–
G
= 0 the
+ I
R
B
G
LT1189 • AI02
(R
R
FB
6
FB
)