LT685
High Speed Comparator
FEATURES
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DESCRIPTIO
Ultrafast (5.5ns typ)
Complementary ECL Output
50Ω Line Driving Capability
Low Offset Voltage
Output Latch Capability
External Hysteresis Control
Pin Compatible with Am685
The LT
®
685 is an ultrafast comparator with differential
inputs and complementary outputs fully compatible with
ECL logic levels. The output current capability is adequate
for driving transmission lines terminated in 50Ω. The low
input offset and high resolution make this comparator
ideally suited for analog-to-digital signal processing
applications.
A latch function is provided to allow the comparator to be
used in a sample-hold mode. When the latch enable input
is ECL high, the comparator functions normally. When the
latch enable is driven low, the comparator outputs are
locked in their existing logical states. If the latch function
is not used, the latch enable must be connected to ground
or ECL high.
The device is pin-compatible with the Am685. Hysteresis
has been added to improve switching time with slow input
signals as well as to minimize oscillation. A single resistor
between the hysteresis pin and V
–
adds input hysteresis
voltage as more current is drawn. If hysteresis is not
required, the pin can be left unconnected.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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High Speed A-to-D Converters
High Speed Sampling Circuits
Oscillators
TYPICAL APPLICATIO
Comparator with Hysteresis
100
6V
GND1
V
+
GND2
V
IN
+
LT685
Q
Q
V
–
HYSTERESIS
R
LATCH
ENABLE
–5.2V
V
T
LT685 • TA01
HYSTERESIS (mV)
10
–
R
L
R
L
1
100
200
U
Hysteresis
HYSTERESIS IS ZERO
IF PIN LEFT OPEN
1k
2k
500
RESISTANCE (Ω)
5k
10k
LT685 • TA02
U
U
685fa
1
LT685
ABSOLUTE
(Note 1)
AXI U
RATI GS
Output Current ...................................................... 30mA
Power Dissipation (Note 2) ................................ 500mW
Operating Temperature
LT685C ......................................... –30°C
≤
T
A
≤
85°C
LT685M
(OBSOLETE)
................. –55°C
≤
T
A
≤
125°C
Positive Supply Voltage ............................................. 7V
Negative Supply Voltage .......................................... –7V
Input Voltage ...........................................................
±4V
Differential Input Voltage .........................................
±6V
Latch Pin Voltage .............................................. 2V to V
–
Hysteresis Pin Voltage ...................................... 0V to V
–
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
GND #1
GND #2
V
+
10
1
9
NONINVERTING 2
INPUT
INVERTING 3
INPUT
4
LATCH
ENABLE
LT685CH
LT685MH
+
–
5
V
–
6
8 Q OUTPUT
7 Q OUTPUT
HYSTERESIS
H PACKAGE
TO-5 METAL CAN
OBSOLETE PACKAGE
Consider the N16 Package as an Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
2
U
U
W
W W
U
W
TOP VIEW
GND #1 1
V
+
2
NON-INVERTING INPUT 3
INVERTING INPUT 4
NC 5
LATCH ENABLE 6
NC 7
V
–
8
N16 PACKAGE
16-LEAD CERDIP
J16 PACKAGE (HERMETIC)
16-LEAD PDIP
16 GND #2
15 NC
14 NC
13 NC
12 Q OUTPUT
11 Q OUTPUT
10 NC
9 HYSTERESIS
ORDER PART
NUMBER
LT685CN
ORDER PART
NUMBER
LT685CJ
LT685MJ
LT685 • POI01
OBSOLETE PACKAGE
Consider the N16 Package as an Alternate Source
685fa
LT685
ELECTRICAL CHARACTERISTICS
erature ranges, unless otherwise noted.
SYMBOL
V
OS
dV
OS
/dT
l
OS
I
B
R
IN
C
IN
V
CM
CMRR
SVRR
V
OH
PARAMETER
Input Offset Voltage
Input Offset Voltage Drift
Input Offset Current
Input Bias Current
Input Resistance
Input Capacitance
lnput Voltage Range
Common Mode Rejection
Supply Voltage Rejection
Output High Voltage
T
A
= 25°C
T
A
= T
MIN
T
A
= T
MAX
T
A
= 25°C
T
A
= T
MIN
T
A
= T
MAX
CONDITIONS
T
A
= 25°C
(Note 3)
T
A
= 25°C
T
A
= 25°C
T
A
= 25°C (Note 3)
T
A
= 25°C (Note 3)
V
+
= 6.0V, V
–
= –5.2V, V
T
= –2V, R
L
= 50Ω, R =
∞
over the operating temp-
LT685C
TYP
1.0
LT685M
TYP
1.0
MIN
MAX
±2.0
±2.5
±10
MIN
MAX
±2.0
±3.0
±10
UNITS
mV
mV
µV/°C
µA
µA
µA
µA
kΩ
0.3
5
6.0
±1.0
±1.3
10
13
6.0
3.0
±3.3
0.3
5
±1.0
±1.6
10
16
3.0
±3.3
80
70
pF
V
dB
dB
80
70
– 0.960
–1.060
– 0.890
–1.850
–1.890
–1.825
–0.810
–0.890
–0.700
–1.650
–1.675
–1.625
22
26
300
–0.960
–1.100
–0.850
–1.850
–1.910
–1.810
–0.810
–0.920
–0.620
–1.650
–1.690
–1.575
22
26
300
V
V
V
V
V
V
mA
mA
mW
V
OL
Output Low Voltage
I
+
I
–
P
DISS
Positive Supply Current
Negative Supply Current
Power Dissipation
685fa
3
LT685
SWITCHI G CHARACTERISTICS
SYMBOL
t
PD
PARAMETER
Propagation Delay
(Note 4)
Latch Enable to
Output Delay
(Note 3)
Minimum Set-Up Time
(Note 3)
Minimum Hold Time
(Note 3)
Minimum Latch Enable
Pulse Width (Note 3)
CONDITIONS
T
A
= 25°C
T
A
= T
MAX
T
A
= T
MIN
T
A
= 25°C
T
A
= T
MAX
T
A
= T
MIN
T
MIN
≤
T
A
≤
25°C
T
A
= T
MAX
T
MIN
≤
T
A
≤
T
MAX
T
MIN
≤
T
A
≤
25°C
T
A
= T
MAX
t
PD(E)
t
S
t
H
t
PW(E)
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
For the metal can package, derate at 6.8mW/°C for operation at
ambient temperatures above 100°C; for the hermetic dual-in-line package,
derate at 9mW/°C for operation at ambient temperatures above 105°C.
Note 3:
Guaranteed by design, but not tested.
Note 4:
Sample tested at 25°C only.
4
U
(V
IN
= 100mV step, 5mV overdrive)
MIN
4.5
5.0
4.0
4.5
5.0
4.0
LT685C
TYP
5.5
MAX
6.5
9.5
6.5
6.5
9.5
6.5
3.0
4.0
1.0
3.0
4.0
MIN
4.5
5.5
3.5
4.5
5.5
3.5
LT685M
TYP
5.5
MAX
6.5
12
6.5
6.5
12
6.5
3.0
6.0
1.0
3.0
5.0
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
5.5
5.5
Definitions:
t
PD
:
The propagation delay measured from the time the input signal
crosses the input offset voltage to the 50% point of the output transition.
t
PD(E)
:
The propagation delay measured from the 50% point of the latch
enable signal positive transition to the 50% point of the output transition.
t
S
:
The minimum time before the negative transition of the latch enable
signal that an input signal change must be present in order to be acquired
and held at the outputs.
t
H
:
The minimum time after the negative transition of the latch enable
signal that the input signal must remain unchanged in order to be acquired
and held at the outputs.
t
PW (E)
:
The minimum time that the latch enable signal must be HIGH in
order to acquire and hold an input signal change.
685fa
LT685
SCHE ATIC DIAGRA
R2
300Ω
D2
Q13
D1
Q33
R22
2.9k
Q3
Q31
Q18
Q30
NONINVERTING
INPUT
INVERTING
INPUT
Q7
Q1
Q5
Q2
R3
1.4k
R4
2.4k
R21
846Ω
Q29
LATCH
ENABLE
Q9
Q10
Q28
Q11
R11
430Ω
Q12
R12
200Ω
R19
2.4k
Q27
R10
880Ω
R14
3k
Q26
R18
150Ω
R13
3.0k
R15
2.1k
R16
2.1k
Q25
R17
150Ω
V
–
HYSTERESIS
LT685 • S01
Q4
Q8
Q6
D5
D6
Q23
Q21
Q16
Q15
Q22
Q24
D7
D8
R7
275Ω
R8
275Ω
W
V
+
R1
300Ω
R23
1.7k
Q14
R6
525Ω
D4
D3
Q32
Q20
Q17
GND #2
GND #1
R5
525Ω
Q19
R20
3.8k
Q
Q
OUTPUT OUTPUT
685fa
W
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