LT1720/LT1721
Dual/Quad,
4.5ns, Single Supply
3V/5V Comparators
with Rail-to-Rail Outputs
FEATURES
s
s
s
s
s
DESCRIPTIO
s
s
s
UltraFast: 4.5ns at 20mV Overdrive
7ns at 5mV Overdrive
Low Power: 4mA per Comparator
Optimized for 3V and 5V Operation
Pinout Optimized for High Speed Ease of Use
Input Voltage Range Extends 100mV
Below Negative Rail
TTL/CMOS Compatible Rail-to-Rail Outputs
Internal Hysteresis with Specified Limits
Low Dynamic Current Drain; 15µA/(V-MHz),
Dominated by Load In Most Circuits
APPLICATIO S
s
s
s
s
s
s
s
High Speed Differential Line Receiver
Crystal Oscillator Circuits
Window Comparators
Threshold Detectors/Discriminators
Pulse Stretchers
Zero-Crossing Detectors
High Speed Sampling Circuits
The LT
®
1720/LT1721 are UltraFast
TM
dual/quad compara-
tors optimized for single supply operation, with a supply
voltage range of 2.7V to 6V. The input voltage range extends
from 100mV below ground to 1.2V below the supply voltage.
Internal hysteresis makes the LT1720/LT1721 easy to use
even with slow moving input signals. The rail-to-rail outputs
directly interface to TTL and CMOS. Alternatively, the sym-
metric output drive can be harnessed for analog applications
or for easy translation to other single supply logic levels.
The LT1720 is available in the 8-pin MSOP and SO packages;
three pins per comparator plus power and ground. The
LT1721 is available in the 16-pin SSOP and S packages.
The pinouts of the LT1720/LT1721 minimize parasitic effects
by placing the most sensitive inputs (inverting) away from the
outputs, shielded by the power rails. The LT1720/LT1721 are
ideal for systems where small size and low power are
paramount.
, LTC and LT are registered trademarks of Linear Technology Corporation.
UltraFast is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
2.7V TO 6V
2k
220Ω
2.7V to 6V Crystal Oscillator with TTL/CMOS Output
8
1MHz TO 10MHz
CRYSTAL (AT-CUT)
7
6
Propagation Delay vs Overdrive
25°C
V
STEP
= 100mV
V
CC
= 5V
C
LOAD
= 10pF
RISING EDGE
(t
PDLH
)
620Ω
+
–
GROUND
CASE
OUTPUT
DELAY (ns)
5
4
3
2
FALLING EDGE
(t
PDHL
)
C1
1/2 LT1720
2k
1720/21 TA01
1
0
0
10
30
OVERDRIVE (mV)
20
40
50
0.01µF
1.8k
U
1720/21 TA02
U
U
1
LT1720/LT1721
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Supply Voltage, V
CC
to GND ...................................... 7V
Input Current ......................................................
±10mA
Output Current (Continuous) .............................
±20mA
Junction Temperature ........................................... 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
Storage Temperature Range ................. – 65°C to 150°C
Operating Temperature Range
C Grade .................................................. 0°C to 70°C
I Grade .............................................. – 40°C to 85°C
PACKAGE/ORDER INFORMATION
TOP VIEW
–IN A
1
2
3
4
5
6
7
8
16 –IN D
15 +IN D
14 V
CC
13 OUT D
12 OUT C
11 V
CC
10 +IN C
9
–IN C
+IN A
GND
TOP VIEW
+IN A
–IN A
–IN B
+IN B
1
2
3
4
8
7
6
5
V
CC
OUT A
OUT B
GND
+IN A 1
–IN A 2
–IN B 3
+IN B 4
8
7
6
5
V
CC
OUT A
OUT B
GND
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 230°C/ W
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 200°C/ W
ORDER PART
NUMBER
LT1720CMS8
MS8
PART MARKING
LTDS
ORDER PART
NUMBER
LT1720CS8
LT1720IS8
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
V
CMR
V
TRIP+
V
TRIP–
V
OS
V
HYST
∆V
OS
/∆T
PARAMETER
Supply Voltage
Common Mode Voltage Range
Input Trip Points
Input Trip Points
Input Offset Voltage
Input Hysteresis Voltage
Input Offset Voltage Drift
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V, V
CM
= 1V, C
OUT
= 10pF, V
OVERDRIVE
= 20mV, unless otherwise specified.
CONDITIONS
q
(Note 2)
(Note 3)
(Note 3)
q
(Note 3)
q
(Note 3)
2
U
U
W
W W
U
W
TOP VIEW
OUT A
OUT B
GND
+IN B
–IN B
GN PACKAGE
16-LEAD NARROW
PLASTIC SSOP
S PACKAGE
16-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 135°C/ W (GN)
T
JMAX
= 150°C,
θ
JA
= 115°C/ W (S)
S8
PART MARKING
1720
1720I
ORDER PART
NUMBER
LT1721CGN
LT1721CS
LT1721IGN
LT1721IS
GN
PART MARKING
1721
1721I
MIN
2.7
– 0.1
– 2.0
– 3.0
– 5.5
– 6.5
q
q
TYP
MAX
6
V
CC
– 1.2
5.5
6.5
2.0
3.0
UNITS
V
V
mV
mV
mV
mV
mV
mV
mV
µV/°C
1.0
q
q
3.0
4.5
5.0
2.0
3.5
10
LT1720/LT1721
ELECTRICAL CHARACTERISTICS
SYMBOL
I
B
I
OS
CMRR
PSRR
A
V
V
OH
V
OL
I
CC
t
PD20
t
PD5
∆t
PD
t
SKEW
t
r
t
f
t
JITTER
f
MAX
PARAMETER
Input Bias Current
Input Offset Current
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Voltage Gain
Output High Voltage
Output Low Voltage
Supply Current (Per Comparator)
Propagation Delay
Propagation Delay
Differential Propagation Delay
Propagation Delay Skew
Output Rise Time
Output Fall Time
Output Timing Jitter
Maximum Toggle Frequency
(Note 4)
(Note 5)
(Note 6)
I
SOURCE
= 4mA, V
IN
= V
TRIP+
+ 10mV
I
SINK
= 10mA, V
IN
= V
TRIP–
– 10mV
V
CC
= 5V
V
CC
= 3V
V
OVERDRIVE
= 20mV (Note 7)
q
q
q
q
q
The
q
denotes specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V, V
CM
= 1V, C
OUT
= 10pF, V
OVERDRIVE
= 20mV, unless otherwise specified.
CONDITIONS
q
q
q
q
MIN
–6
55
65
V
CC
– 0.4
TYP
MAX
0
0.6
UNITS
µA
µA
dB
dB
V
70
80
∞
0.4
4
3.5
4.5
7
q
V
mA
mA
ns
ns
ns
ns
ns
ns
ns
ns
ps
RMS
ps
RMS
MHz
MHz
7
6
6.5
8.0
10
13
1.0
1.5
V
OVERDRIVE
= 5mV (Notes 7, 8)
(Note 9) Between Channels
(Note 10) Between t
PD PD
10% to 90%
90% to 10%
V
IN
= 1.2V
P-P
(6dBm), Z
IN
= 50Ω
V
CM
= 2V, f = 20MHz
V
OVERDRIVE
= 50mV, V
CC
= 3V
V
OVERDRIVE
= 50mV, V
CC
= 5V
t
PD+
t
PD–
+
/t
–
0.3
0.5
2.5
2.2
15
11
70.0
62.5
Note 1:
Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2:
If one input is within these common mode limits, the other
input can go outside the common mode limits and the output will be
valid.
Note 3:
The LT1720/LT1721 comparators include internal hysteresis.
The trip points are the input voltage needed to change the output state
in each direction. The offset voltage is defined as the average of V
TRIP+
and V
TRIP–
, while the hysteresis voltage is the difference of these two.
Note 4:
The common mode rejection ratio is measured with V
CC
= 5V
and is defined as the change in offset voltage measured from V
CM
=
– 0.1V to V
CM
= 3.8V, divided by 3.9V.
Note 5:
The power supply rejection ratio is measured with V
CM
= 1V
and is defined as the change in offset voltage measured from V
CC
=
2.7V to V
CC
= 6V, divided by 3.3V.
Note 6:
Because of internal hysteresis, there is no small-signal region
in which to measure gain. Proper operation of internal circuity is
ensured by measuring V
OH
and V
OL
with only 10mV of overdrive.
Note 7:
Propagation delay measurements made with 100mV steps.
Overdrive is measured relative to V
TRIP
±
.
Note 8:
t
PD
cannot be measured in automatic handling equipment with
low values of overdrive. The LT1720/LT1721 are 100% tested with a
100mV step and 20mV overdrive. Correlation tests have shown that
t
PD
limits can be guaranteed with this test, if additional DC tests are
performed to guarantee that all internal bias conditions are correct.
Note 9:
Differential propagation delay is defined as the larger of the
two:
∆t
PDLH
= t
PDLH(MAX)
– t
PDLH(MIN)
∆t
PDHL
= t
PDHL(MAX)
– t
PDHL(MIN)
where (MAX) and (MIN) denote the maximum and minimum values of
a given measurement across the different comparator channels.
Note 10:
Propagation Delay Skew is defined as:
t
SKEW
= |t
PDLH
– t
PDHL
|
3
LT1720/LT1721
TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset and Trip Voltages
vs Supply Voltage
3
V
OS
AND TRIP POINT VOLTAGE (mV)
COMMON MODE INPUT VOLTAGE (V)
V
OS
AND TRIP POINT VOLTAGE (mV)
V
TRIP+
2
1
V
OS
0
–1
–2
–3
2.5
V
TRIP–
25°C
V
CM
= 1V
3.0
5.0
3.5 4.0 4.5
SUPPLY VOLTAGE (V)
5.5
6.0
QUIESCENT SUPPLY CURRENT PER COMPARATOR (mA)
Input Current
vs Differential Input Voltage
2
1
0
25°C
V
CC
= 5V
SUPPLY CURRENT PER COMPARATOR (mA)
INPUT CURRENT (µA)
–1
–2
–3
–4
–5
–6
–7
– 5 – 4 – 3 – 2 –1 0 1 2 3 4
DIFFERENTIAL INPUT VOLTAGE (V)
5
Propagation Delay
vs Load Capacitance
9
8
7
6
25°C
V
STEP
= 100mV
OVERDRIVE = 20mV
V
CC
= 5V
RISING EDGE
(t
PDLH
)
PROPAGATION DELAY (ns)
DELAY (ns)
5
4
3
2
1
0
0
FALLING EDGE
(t
PDHL
)
DELAY (ns)
40
30
OUTPUT LOAD CAPACITANCE (pF)
10
20
4
U W
1720/21 G01
1720/21 G04
1720/21 G07
Input Offset and Trip Voltages
vs Temperature
3
2
1
V
OS
0
–1
–2
–3
–50
V
TRIP+
Input Common Mode Limits
vs Temperature
4.2
V
CC
= 5V
4.0
3.8
3.6
0.2
0
– 0.2
– 0.4
– 50 – 25
V
TRIP–
– 25
0
50
75
25
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
1720/21 G02
1720/21 G03
Quiescent Supply Current
vs Temperature
6.0
5.5
5.0
4.5
V
CC
= 5V
4.0
V
CC
= 3V
3.5
3.0
2.5
2.0
– 50 – 25
0
75
50
25
TEMPERATURE (˚C)
100
125
7
6
5
4
3
2
1
0
Quiescent Supply Current
vs Supply Voltage
125°C
25°C
– 55°C
0
1
4
3
2
5
SUPPLY VOLTAGE (V)
6
7
1720/21 G05
1720/21 G06
Propagation Delay
vs Temperature
8.0
7.5
V
CC
= 3V
7.0
6.5
6.0
5.5
V
CC
= 5V
5.0
OVERDRIVE = 20mV
4.5
50
Propagation Delay
vs Supply Voltage
t
PDLH
V
CM
= 1V
V
STEP
= 100mV
C
LOAD
= 10pF
5.0
25°C
V
STEP
= 100mV
OVERDRIVE = 20mV
C
LOAD
= 10pF
V
CC
= 5V
OVERDRIVE = 5mV
4.5
RISING EDGE
(t
PDLH
)
FALLING EDGE
(t
PDHL
)
4.0
2.5
V
CC
= 3V
4.0
75
0
50
25
– 50 – 25
TEMPERATURE (°C)
100
125
3.0
3.5 4.0 4.5 5.0
SUPPLY VOLTAGE (V)
5.5
6.0
1720/21 G08
1720/21 G09
LT1720/LT1721
TYPICAL PERFORMANCE CHARACTERISTICS
Output Low Voltage
vs Load Current
0.5
0.0
SUPPLY CURRENT PER COMPARATOR (mA)
OUTPUT VOLTAGE RELATIVE TO V
CC
(V)
V
CC
= 5V
V
CM
= 1V
V
IN
= – 15mV
OUTPUT VOLTAGE (V)
0.4
125°C
V
CC
= 2.7V
25°C
– 55°C
0.3
0.2
0.1
0
4
12
16
8
OUTPUT SINK CURRENT (mA)
PIN FUNCTIONS
LT1720
+IN A (Pin 1):
Noninverting Input of Comparator A.
–IN A (Pin 2):
Inverting Input of Comparator A.
–IN B (Pin 3):
Inverting Input of Comparator B.
+IN B (Pin 4):
Noninverting Input of Comparator B.
GND (Pin 5):
Ground.
OUT B (Pin 6):
Output of Comparator B.
OUT A (Pin 7):
Output of Comparator A.
V
CC
(Pin 8):
Positive Supply Voltage.
LT1721
–IN A (Pin 1):
Inverting Input of Comparator A.
+IN A (Pin 2):
Noninverting Input of Comparator A.
GND (Pins 3, 6):
Ground.
OUT A (Pin 4):
Output of Comparator A.
OUT B (Pin 5):
Output of Comparator B.
+IN B (Pin 7):
Noninverting Input of Comparator B.
–IN B (Pin 8):
Inverting Input of Comparator B.
–IN C (Pin 9):
Inverting Input of Comparator C.
+IN C (Pin 10):
Noninverting Input of Comparator C.
V
CC
(Pins 11, 14):
Positive Supply Voltage.
OUT C (Pin 12):
Output of Comparator C.
OUT D (Pin 13):
Output of Comparator D.
+IN D (Pin 15):
Noninverting Input of Comparator D.
–IN D (Pin 16):
Inverting Input of Comparator D.
U W
125°C
1720/21 G10
Output High Voltage
vs Load Current
10
9
8
V
CC
= 5V
V
CM
= 1V
V
IN
= 15mV
– 55°C
– 0.4
25°C
Supply Current vs Frequency
25°C
V
CC
= 5V
– 0.2
125°C
C
LOAD
= 20pF
7
6
NO LOAD
5
4
3
– 0.6
– 0.8
25°C
V
CC
= 2.7V
–1.0
0
4
12
16
8
OUTPUT SOURCE CURRENT (mA)
20
20
0
10
20
FREQUENCY (MHz)
30
40
1720/21 G12
1720/21 G11
U
U
U
5
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