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Final Electrical Specifications
LT1394 7ns, Low Power, Single Supply, Ground-Sensing Comparator
FEATURES
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DESCRIPTION
May 1998
Ultrafast: 7ns Low Power: 6mA Low Offset Voltage: 0.8mV Operates Off Single 5V or Dual 5V Supplies Input Common Mode Extends to Negative Supply No Minimum Slew Rate Requirement Complementary TTL Outputs Inputs Can Exceed Supplies without Phase Reversal Pin Compatible with LT1016 and LT1116 Output Latch Capability Available in SO-8 Package
APPLICATIONS
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High Speed A/D Converters Zero-Crossing Detectors Current Sense for Switching Regulators Extended Range V/F Coverters Fast Pulse Height/Width Discriminators High Speed Triggers Line Receivers High Speed Sampling Circuits
, LTC and LT are registered trademarks of Linear Technology Corporation. UltraFast is a trademark of Linear Technology Corporation.
The LT (R)1394 is an UltraFastTM (7ns) comparator with complementary outputs and latch. The input common mode range extends from 1.5V below the positive supply down to the negative supply rail. Like the LT1016 and LT1116, this comparator has complementary outputs designed to interface directly to TTL or CMOS logic. The LT1394 may operate from either a single 5V supply or dual 5V supplies. Low offset voltage specifications and high gain allow the LT1394 to be used in precision applications. The LT1394 is designed for improved speed and stability for a wide range of operating conditions. The output stage provides active drive in both directions for maximum speed into TTL, CMOS or passive loads with minimal cross-conduction current. Unlike other fast comparators, the LT1394 remains stable even for slow transitions through the active region, which eliminates the need to specify a minimum input slew rate. The LT1394 has an internal, TTL/CMOS compatible latch for retaining data at the outputs. The latch holds data as long as the LATCH pin is held high. Device parameters such as gain, offset and negative power supply current are not significantly affected by variations in negative supply voltage.
TYPICAL APPLICATION
14.31818MHz (4X NTSC) Voltage Tunable Crystal Oscillator
5V 1N4148 1M C SELECT*** 0.047F MV-209 1M 47k*
12
Propagation Delay vs Input Overdrive
3.9k* 1k*
VIN 0V TO 5V
1M*
LT1004-2.5
10 8
TIME (ns)
5V 2k 100pF
1M
6 4
Y1**
390
+
LT1394
15pF
100pF
2
-
2k 200pF
FREQUENCY OUTPUT * 1% FILM RESISTOR ** NORTHERN ENGINEERING LABS C-2350N-14.31818MHz *** C SELECT SETS TUNING BANDWIDTH. SET TO COMPLEMENT LOOP RESPONSE IN PHASE LOCKING APPLICATIONS VARACTOR DIODE 1394 TA01
0
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
0
U
U
TJ = 25C VSTEP = 100mV VS = 5V
tPDLH tPDHL
10
20 30 OVERDRIVE (mV)
40
50
1394 TA02
1
LT1394
ABSOLUTE MAXIMUM RATINGS
Positive Supply Voltage ............................................. 7V Negative Supply Voltage .......................................... - 7V Total Supply Voltage (V + to V -) .............................. 12V Differential Input Voltage ....................................... 12V Input and Latch Current ...................................... 10mA Output Current (Continuous) .............................. 20mA Operating Temperature Range ..................... 0C to 70C Junction Temperature ........................................... 150C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec.)................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW V+ 1 +IN 2 -IN 3 V- 4 + 8 Q OUT 7 Q OUT 6 GND 5 LATCH ENABLE
ORDER PART NUMBER LT1394CS8 S8 PART MARKING 1394
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 150C, JA = 190C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
V + = 5V, V - = - 5V, VOUT(Q) = 1.4V, VLATCH = VCM = 0V, TA = 25C unless otherwise noted.
SYMBOL VOS VOS T IOS IB IVR CMRR PARAMETER Input Offset Voltage Input Offset Voltage Drift Input Offset Current
q
CONDITIONS RS 100 (Note 1)
q q
MIN
TYP 0.8 4 0.1
MAX 2.5 4.0
UNITS mV mV V/C
0.5 0.8 4.5 7.0 3.5 3.5
Input Bias Current Input Voltage Range
(Note 2)
q q q
2 -5 0 100
q
Single 5V Supply Common Mode Rejection Ratio - 5V VCM 3.5V
55 100 55 65 50 100 65 750 1600 3.1 3.0 0.3 0.4 6 0.5 8.5 10.0 2.2 2.5
Single 5V Supply 0V VCM 3.5V PSRR Power Supply Rejection Ratio 4.6V V + 5.4V
q
q
- 7V V - - 2V
q
AV VOH VOL I+ I-
Small Signal Voltage Gain Output Voltage Swing High Output Voltage Swing Low Positive Supply Current
1V VOUT 2V V + 4.6V, IOUT = 1mA V + 4.6V, IOUT = 4mA IOUT = - 4mA IOUT = - 10mA
q q q
2.7 2.4
q
Negative Supply Current
q
1.2
2
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W
U
-
U
WW
W
A A A A V V dB dB dB dB dB dB dB dB V/V V V V V mA mA mA mA
LT1394
ELECTRICAL CHARACTERISTICS
V + = 5V, V - = - 5V, VOUT(Q) = 1.4V, VLATCH = VCM = 0V, TA = 25C unless otherwise noted.
SYMBOL VIH VIL IIL t PD t PD t LPD t SU tH t PW(D) PARAMETER LATCH Pin High Input Voltage LATCH Pin Low Input Voltage LATCH Pin Current Propagation Delay (Note 3) Differential Propagation Delay (Note 3) Latch Propagation Delay (Note 4) Latch Setup Time (Note 4) Latch Hold Time (Note 4) Minimum Disable Pulse Width VLATCH = 0V VIN = 100mV, VOD = 5mV
q
CONDITIONS
q q q
MIN 2
TYP
MAX
UNITS V
0.8 -4 7 0.5 6 - 0.4 2 3 - 10 9 14 2.2
V A ns ns ns ns ns ns ns
VIN = 100mV, VOD = 5mV
The q denotes specifications that apply over the full operating temperature range. Note 1: Input offset voltage (VOS) is defined as the average of the two voltages measured by forcing first one output, then the other to 1.4V. Note 2: Input bias current (IB) is defined as the average of the two input currents. Note 3: tPD and tPD cannot be measured in automatic handling equipment with low values of overdrive. The LT1394 is 100% tested with a 100mV step and 20mV overdrive. Correlation tests have shown that tPD and tPD limits can be guaranteed with this test, if additional DC tests are
performed to guarantee that all internal bias conditions are correct. Propagation delay (t PD) is measured with the overdrive added to the actual VOS. Differential propagation delay is defined as: t PD = t PD+ - tPD- Note 4: Latch propagation delay (t LPD) is the delay time for the output to respond when the LATCH pin is deasserted. Latch setup time (t SU) is the interval in which the input signal must remain stable prior to asserting the latch signal. Latch hold time (tH) is the interval after the latch is asserted in which the input signal must remain stable.
TYPICAL PERFORMANCE CHARACTERISTICS
Gain Characteristics
5.0 4.5 4.0 IOUT = 0 VS = 5V TJ = 25C
OUTPUT VOLTAGE (V)
3.5
TIME (ns)
TIME (ns)
3.0 2.5 2.0 1.5 1.0 0.5 0 -3 -2 0 1 2 -1 DIFFERENTIAL INPUT VOLTAGE (mV) 3
UW
1394 G01
Propagation Delay vs Load Capacitance
12 10 tPDLH 8 6 4 2 0 tPDHL 12 10 8 6 4 2 0 0 10 20 30 40 OUTPUT LOAD CAPACITANCE (pF) 50
1394 G02
Propagation Delay vs Positive Supply Voltage
tPDHL tPDLH
IOUT = 0 VS = 5V TJ = 25C VSTEP = 100mV OVERDRIVE = 5mV
V - = -5V TJ = 25C VSTEP = 100mV OVERDRIVE = 5mV 4.4 4.6 4.8 5.0 5.2 5.4 POSITIVE SUPPLY VOLTAGE (V) 5.6
1394 G03
3
LT1394
APPLICATIONS INFORMATION
Common Mode Considerations The LT1394 is specified for a common mode range of - 5V to 3.5V on a 5V supply or a common mode range of 0V to 3.5V on a single 5V supply. A more general consideration is that the common mode range is 0V below the negative supply and 1.5V below the positive supply, independent of the actual supply voltage. The criterion for common mode limit is that the output still responds correctly to a small differential input signal. When either input signal falls below the negative common mode limit, the internal PN diode formed with the substrate can turn on, resulting in significant current flow through the die. An external Schottky clamp diode between the input and the negative rail can speed up recovery from negative overdrive by preventing the substrate diode from turning on. Either input may go above the positive common mode limit without damaging the comparator as long as it does not go far enough above the positive supply to conduct more than 10mA. Functionality will continue if the remaining input stays within the allowed common mode range. There will, however, be an increase in propagation delay as the input signal switches back into the common mode range. Input Bias Current Input bias current is measured with the output held at 1.4V. As with any PNP differential input stage, the LT1394 bias current flows out of the device. It will go to zero on an input which is high and double on an input which is low. LATCH Pin Dynamics The LATCH pin is intended to retain input data (output latched) when the LATCH pin goes high. The pin will float to a high state when disconnected, so a flow-through condition requires that the LATCH pin be grounded. The LATCH pin is designed to be driven with either a TTL or CMOS output. It has no built-in hysteresis. High Speed Design Techniques A substantial amount of design effort has made the LT1394 relatively easy to use. It is much less prone to oscillation than some slower comparators, even with slow input signals. However, as with any high speed comparator, there are a number of problems which may arise because of PC board layout and design. The most common problem involves power supply bypassing. Bypassing is necessary to maintain low supply impedance. DC resistance and inductance in supply wires and PC traces can quickly build up to unacceptable levels. This allows the supply line to move with changing internal current levels of the connected devices. This will almost always result in improper operation. In addition, adjacent devices connected through an unbypassed supply can interact with each other through the finite supply impedances. Bypass capacitors furnish a simple solution to this problem by providing a local reservoir of energy at the device, keeping supply impedances low. Bypass capacitors should be as close as possible to the LT1394. A good high frequency capacitor such as a 0.1F ceramic is recommended, in parallel with a larger capacitor such as a 4.7F tantalum. Poor trace routes and high source impedances are also common sources of problems. Be sure to keep trace lengths as short as possible, and avoid running any output trace adjacent to an input trace to prevent unnecessary coupling. If output traces are longer than a few inches, be sure to terminate them with a resistor to eliminate any reflections that may occur. Resistor values are typically 250 to 400. Also, be sure to keep source impedances as low as possible, preferably 1k or less.
RELATED PARTS
PART NUMBER LT1016 LT1116 DESCRIPTION Ultrafast Precision Comparator 12ns Single Supply Ground-Sensing Comparator COMMENTS Industry Standard 10ns Comparator Single Supply Version of LT1016
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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1394i LT/TP 0598 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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