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Single-Supply, High Speed PECL/LVPECL Comparators ADCMP551/ADCMP552/ADCMP553
FEATURES
Single power supply 500 ps propagation delay input to output 125 ps overdrive dispersion Differential PECL/LVPECL compatible outputs Differential latch control Internal latch pull-up resistors Power supply rejection greater than 70 dB 700 ps minimum pulse width Equivalent input rise time bandwidth > 750 MHz Typical output rise/fall of 500 ps Programmable hysteresis
FUNCTIONAL BLOCK DIAGRAM
HYS* NONINVERTING INPUT Q OUTPUT
INVERTING INPUT
ADCMP551/ ADCMP552/ ADCMP553
Q OUTPUT
*ADCMP552 ONLY
Figure 1.
GENERAL DESCRIPTION APPLICATIONS
Automatic test equipment High speed instrumentation Scope and logic analyzer front ends Window comparators High speed line receivers Threshold detection Peak detection High speed triggers Patient diagnostics Disk drive read channel detection Hand-held test instruments Zero-crossing detectors Line receivers and signal restoration Clock drivers
The ADCMP551/ADCMP552/ADCMP553 are single-supply, high speed comparators fabricated on Analog Devices' proprietary XFCB process. The devices feature a 500 ps propagation delay with less than 125 ps overdrive dispersion. Overdrive dispersion, a measure of the difference in propagation delay under differing overdrive conditions, is a particularly important characteristic of high speed comparators. A separate programmable hysteresis pin is available on the ADCMP552. A differential input stage permits consistent propagation delay with a common-mode range from -0.2 V to VCCI - 2.0 V. Outputs are complementary digital signals and are fully compatible with PECL and 3.3V LVPECL logic families. The outputs provide sufficient drive current to directly drive transmission lines terminated in 50 to VCCO - 2 V. A latch input is included and permits tracking, track-and-hold, or sample-and-hold modes of operation. The latch input pins contain internal pull-ups that set the latch in tracking mode when left open. The ADCMP551/ADCMP552/ADCMP553 are specified over the -40C to +85C industrial temperature range. The ADCMP551 is available in a 16-lead QSOP package; the ADCMP552 is available in a 20-lead QSOP package; and the ADCMP553 is available in an 8-lead MSOP package.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
04722-001
LATCH ENABLE INPUT
LATCH ENABLE INPUT
ADCMP551/ADCMP552/ADCMP553 TABLE OF CONTENTS
Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Considerations.............................................................. 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristics ............................................. 8 Timing Information ....................................................................... 10 Application Information................................................................ 11 Clock Timing Recovery............................................................. 11 Optimizing High Speed Performance ..................................... 11 Comparator Propagation Delay Dispersion ........................... 11 Comparator Hysteresis .............................................................. 12 Minimum Input Slew Rate Requirement ................................ 12 Typical Application Circuits ......................................................... 13 Outline Dimensions ....................................................................... 14 Ordering Guide .......................................................................... 14
REVISION HISTORY
10/04--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADCMP551/ADCMP552/ADCMP553 SPECIFICATIONS
VCCI = 3.3 V, VCCO = 3.3 V, TA = 25C, unless otherwise noted. Table 1. Electrical Characteristics
Parameter DC INPUT CHARACTERISTICS Input Voltage Range Input Differential Voltage Range Input Offset Voltage Input Offset Voltage Channel Matching Offset Voltage Tempco Input Bias Current Input Bias Current Tempco Input Offset Current Input Capacitance Input Resistance, Differential Mode Input Resistance, Common Mode Active Gain Common-Mode Rejection Ratio Hysteresis LATCH ENABLE CHARACTERISTICS Latch Enable Voltage Range Latch Enable Differential Voltage Range Latch Enable Input High Current Latch Enable Input Low Current LE Voltage, Open LE Voltage, Open Latch Setup Time Latch Hold Time Latch to Output Delay Latch Minimum Pulse Width DC OUTPUT CHARACTERISTICS Output Voltage--High Level Output Voltage--Low Level AC OUTPUT CHARACTERISTICS Rise Time Fall Time AC OUTPUT CHARACTERISTICS (ADCMP553) Rise Time Fall Time AC PERFORMANCE Propagation Delay Propagation Delay Tempco Prop Delay Skew--Rising Transition to Falling Transition Within Device Propagation Delay Skew--Channel-to-Channel Overdrive Dispersion Overdrive Dispersion Slew Rate Dispersion Pulse Width Dispersion Duty Cycle Dispersion Common-Mode Voltage Dispersion Symbol Conditions Min -0.2 -3 -10.0 Typ Max VCCI - 2.0 +3 +10.0 Unit V V mV mV V/C A nA/C A pF k k dB dB mV V V A A V V ps ps ps ps V V ps ps ps ps ps ps ps/C ps ps ps ps ps ps ps ps
VOS VOS/dT IIN
-IN = 0 V, +IN = 0 V
-IN = -0.2 V, +IN = +1.3 V
-28.0 -3.0
CIN
AV CMRR
VCM = -0.2 V to +1.3 V RHYS = VCCI - 1.8 0.4 -150 -150 VCCI - 0.15 VCCI/2 - 0.075
2.0 1.0 2.0 -6.0 -5.0 1.0 1.0 1800 1000 60 76 0.5
+5.0 +3.0
tS tH tPLOH, tPLOL tPL VOH VOL tR tF tR tF tPD tPD/dT
@ VCCI - 0.8 V @ VCCI - 1.8 V Latch inputs not connected Latch inputs not connected VOD = 250 mV VOD = 250 mV VOD = 250 mV VOD = 250 mV PECL 50 to VDD - 2.0 V PECL 50 to VDD - 2.0 V 10% to 90% 10% to 90% 10% to 90% 10% to 90% VOD = 1 V VOD = 20 mV VOD = 1 V VOD = 1 V VOD = 1 V 20 mV VOD 100 mV 50 mV VOD 1.0 V 0.4 V/ns SR 1.33 V/ns 700 ps PW 10 ns 33 MHz, 1 V/ns, VCM = 0.5 V 1 V swing, 0.3 V VCM 0.8 V
Rev. 0 | Page 3 of 16
VCCI - 0.8 1.0 +150 +150 VCCI VCCI/2 + 0.075 100 100 450 700
VCCO - 1.15 VCCO - 2.00 510 490 440 410 500 625 0.25 35 35 75 75 75 25 10 10
VCCO - 0.78 VCCO - 1.54
ADCMP551/ADCMP552/ADCMP553
Parameter AC PERFORMANCE (continued) Equivalent Input Rise Time Bandwidth1 Maximum Toggle Rate Minimum Pulse Width RMS Random Jitter Unit-to-Unit Propagation Delay Skew POWER SUPPLY (ADCMP551/ADCMP552) Input Supply Current Output Supply Current Output Supply Current Input Supply Voltage Output Supply Voltage Positive Supply Differential Power Dissipation Power Dissipation DC Power Supply Rejection Ratio--VCCI DC Power Supply Rejection Ratio--VCCO POWER SUPPLY (ADCMP553) Positive Supply Current Positive Supply Current Positive Supply Voltage Power Dissipation Power Dissipation DC Power Supply Rejection Ratio--VCC HYSTERESIS (ADCMP552 Only) Programmable Hysteresis Symbol BWEQ PWMIN Conditions 0 V to 1 V swing, 2 V/ns >50% output swing tPD < 25 ps VOD = 250 mV, 1.3 V/ns, 500 MHz, 50% duty cycle Min Typ 750 800 700 1.1 50 IVCCI IVCCO VCCI VCCO VCCO - VCCI PD PSRRVCCI PSRRVCCO IVCC VCC PD PSRRVCC 0 @ 3.3 V without load @ 3.3 V with load Dual Dual, without load Dual, with load @ 3.3 V @ 3.3 V without load @ 3.3 V with load Dual Dual Dual, without load Dual, with load 8 3 40 3.135 3.135 -0.2 40 90 12 5 55 3.3 3.3 55 110 75 85 9 35 3.3 30 60 70 17 9 70 5.25 5.25 +2.3 75 130 Max Unit MHz MHz ps ps ps mA mA mA V V V mW mW dB dB mA mA V mW mW dB mV
3.135
13 42 5.25 42 75
40
1
Equivalent input rise time bandwidth assumes a first order input response and is calculated by the following formula: BWEQ = .22/ (trCOMP2 - trIN2), where trIN is the 20/80 input transition time applied to the comparator and trCOMP is the effective transition time as digitized by the comparator input.
Rev. 0 | Page 4 of 16
ADCMP551/ADCMP552/ADCMP553 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Supply Voltages Input Supply Voltage (VCCI to GND) Output Supply Voltage (VCCO to GND) Ground Voltage Differential Input Voltages Input Common-Mode Voltage Differential Input Voltage Input Voltage, Latch Controls Output Output Current Temperature Operating Temperature, Ambient Operating Temperature, Junction Storage Temperature Range Rating -0.5 V to +6.0 V -0.5 V to +6.0 V -0.5 V to +0.5 V -0.5 V to +3.5 V -4.0 V to +4.0 V -0.5 V to +5.5 V 30 mA -40C to +85C 125C -65C to +150C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
THERMAL CONSIDERATIONS
The ADCMP551 16-lead QSOP package has a JA (junction-toambient thermal resistance) of 104C/W in still air. The ADCMP552 20-lead QSOP package has a JA (junction-toambient thermal resistance) of 80C/W in still air. The ADCMP553 8-lead MSOP package has a JA (junction-toambient thermal resistance) of 130C/W in still air.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 5 of 16
ADCMP551/ADCMP552/ADCMP553 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VCCO 1
QA 1 QA 2 VCCO 3 LEA 4 LEA 5 VCCI 6 -INA 7 +INA 8
16 QB 15 QB 14 VCCO
20 19 18
VCCO QB QB VCCO LEB LEB AGND -INB
04722-003
QA 2 QA 3 VCCO 4 LEA 5 LEA 6 VCCI 7 -INA 8
04722-002
ADCMP552
TOP VIEW (Not to Scale)
17 16 15 14 13 12 11
LEA 1 LEA 2 +INA 3 -INA 4
8 AGND
ADCMP551
TOP VIEW (Not to Scale)
ADCMP553
TOP VIEW (Not to Scale)
7 VCC 6 QA 5 QA
04722-004
13 LEB 12 LEB 11 AGND 10 -INB 9
+INB
+INA 9 HYSA 10
+INB HYSB
Figure 2. ADCMP551 16-Lead QSOP Pin Configuration
Figure 3. ADCMP552 20-Lead QSOP Pin Configuration
Figure 4. ADCMP553 8-Lead MSOP Pin Configuration
Table 3. Pin Function Descriptions
ADCMP551 3, 14 1 Pin No. ADCMP552 1, 4, 17, 20 2 ADCMP553 6 Mnemonic VCCO QA Function Logic Supply Terminal. One of Two Complementary Outputs for Channel A. QA is logic high if the analog voltage at the noninverting input is greater than the analog voltage at the inverting input (provided the comparator is in the compare mode). See the description of Pin LEA for more information. One of Two Complementary Outputs for Channel A. QA is logic low if the analog voltage at the noninverting input is greater than the analog voltage at the inverting input (provided the comparator is in the compare mode). See the description of Pin LEA for more information. One of Two Complementary Outputs for Channel A Latch Enable. In the compare mode (logic high), the output tracks changes at the input of the comparator. In the latch mode (logic low), the output reflects the input state just prior to the comparator's being placed in the latch mode. LEA must be driven in conjunction with LEA. One of Two Complementary Outputs for Channel A Latch Enable. In the compare mode (logic high), the output tracks changes at the input of the comparator. In the latch mode (logic low), the output reflects the input state just prior to the comparator's being placed in the latch mode. LEA must be driven in conjunction with LEA. Input Supply Terminal. Inverting Analog Input of the Differential Input Stage for Channel A. The inverting A input must be driven in conjunction with the noninverting A input. Noninverting Analog Input of the Differential Input Stage for Channel A. The noninverting A input must be driven in conjunction with the inverting A input. Programmable Hysteresis. Programmable Hysteresis. Noninverting Analog Input of the Differential Input Stage for Channel B. The noninverting B input must be driven in conjunction with the inverting B input. Inverting Analog Input of the Differential Input Stage for Channel B. The inverting B input must be driven in conjunction with the noninverting B input. Analog Ground.
2
3
5
QA
4
5
2
LEA
5
6
1
LEA
6 7 8
7 8 9 10 11 12 13 14
4 3
VCCI -INA +INA HYSA HYSB +INB -INB
9 10 11
8
AGND
Rev. 0 | Page 6 of 16
ADCMP551/ADCMP552/ADCMP553
ADCMP551 12 Pin No. ADCMP552 15 ADCMP553 Mnemonic LEB Function One of Two Complementary Inputs for Channel B Latch Enable. In the compare mode (logic low), the output tracks changes at the input of the comparator. In the latch mode (logic high), the output reflects the input state just prior to the comparator's being placed in the latch mode. LEB must be driven in conjunction with LEB. One of Two Complementary Inputs for Channel B Latch Enable. In the compare mode (logic low), the output tracks changes at the input of the comparator. In the latch mode (logic high), the output reflects the input state just prior to the comparator's being placed in the latch mode. LEB must be driven in conjunction with LEB. One of Two Complementary Outputs for Channel B. QB is logic low if the analog voltage at the noninverting input is greater than the analog voltage at the inverting input (provided the comparator is in the compare mode). See the description of Pin LEB for more information. One of Two Complementary Outputs for Channel B. QB is logic high if the analog voltage at the noninverting input is greater than the analog voltage at the inverting input (provided the comparator is in the compare mode). See the description of Pin LEB for more information. Positive Supply Terminal.
13
16
LEB
15
18
QB
16
19
QB
7
VCC
Rev. 0 | Page 7 of 16
ADCMP551/ADCMP552/ADCMP553 TYPICAL PERFORMANCE CHARACTERISTICS
VCCI = 3.3 V, VCCO = 3.3 V, TA = 25C, unless otherwise noted.
-5
-6.5 -6.6
+IN INPUT BIAS CURRENT (A) (+IN = 0.5V, -IN = 0V)
04722-005
-6
-6.7 -6.8 -6.9 -7.0 -7.1 -7.2 -7.3 -7.4 -7.5 -40
04722-008
INPUT BIAS CURRENT (A)
-7
-8
-9
-10 -0.2 0.1 0.4 0.7 1.0 1.3 NONINVERTING INPUT VOLTAGE (INVERTING VOLTAGE = 0.5V)
-20
0
20 40 TEMPERATURE (C)
60
80
Figure 5. Input Bias Current vs. Input Voltage
2.00 1.95 1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 -40
04722-006
Figure 8. Input Bias Current vs. Temperature
2.4 2.3 RISE 2.2
OUTPUT RISE AND FALL (V)
OFFSET VOLTAGE (mV)
2.1 2.0 1.9 1.8 1.7 FALL 1.6 1.5 1.4 0 0.25 0.50 0.75 1.00 TIME (ns) 1.25 1.50
04722-012
-20
0
20 40 TEMPERATURE (C)
60
80
1.75
Figure 6. Input Offset Voltage vs. Temperature
Figure 9. Rise and Fall of Outputs vs. Time
460 525 450 515 RISE
TIME (ps)
RISE 440
TIME (ps)
505
430
495 FALL 485
04722-007
420 FALL 410
04722-010
475 -40 -30 -20 -10
0
10 20 30 40 50 TEMPERATURE (C)
60
70
80
90
400 -40 -30 -20 -10
0
10 20 30 40 50 TEMPERATURE (C)
60
70
80
90
Figure 7. ADCMP551/2 Rise/Fall Time vs. Temperature
Figure 10. ADCMP553 Rise/Fall Time vs. Temperature
Rev. 0 | Page 8 of 16
ADCMP551/ADCMP552/ADCMP553
515 505 504 510 503
PROPAGATION DELAY (ps) PROPAGATION DELAY (ps)
04722-011
505
502 501 500 499 498 497 496 495 -0.2
04722-014
500
495
490
485
480 -40 -30 -20 -10
0
10 20 30 40 50 TEMPERATURE (C)
60
70
80
90
0.1 0.4 0.7 1.0 INPUT COMMON MODE VOLTAGE (V)
1.3
Figure 11. Propagation Delay vs. Temperature
140
Figure 14. Propagation Delay vs. Common-Mode Voltage
25
PROPAGATION DELAY ERROR (ps)
100
PROPAGATION DELAY ERROR (ps)
120
20
15
80
10
60
5
40
04722-012
0 0 0.2 0.4 0.6 OVERDRIVE VOLTAGE (V) 0.8 1.0
-5 0.7
1.7
2.7
3.7
4.7 5.7 6.7 PULSE WIDTH (ns)
7.7
8.7
9.7
Figure 12. Propagation Delay vs. Overdrive Voltage
120 140
Figure 15. Propagation Delay Error vs. Pulse Width
PROGRAMMED HYSTERESIS (mV)
PROGRAMMED HYSTERESIS (mV)
100
120
100
80
80
60
60
40
40
20
04722-009
0 100
10 RHYS (k)
1
0 0 50 100 150 IHYS (A) 200 250
300
Figure 13. Comparator Hysteresis vs. RHYS
Figure 16. Comparator Hysteresis vs. IHYS
Rev. 0 | Page 9 of 16
04722-025
20
04722-015
20
0
ADCMP551/ADCMP552/ADCMP553 TIMING INFORMATION
LATCH ENABLE 50% LATCH ENABLE
tS tH
tPL
DIFFERENTIAL INPUT VOLTAGE
VIN VOD
VREF VOS
tPDL
Q OUTPUT
tPLOH
50%
tPDH
tF
50%
Q OUTPUT
tR
Figure 17. System Timing Diagram
Figure 17 shows the compare and latch features of the ADCMP55x family. Table 4 describes the terms in the diagram. Table 4. Timing Descriptions
Symbol tPDH tPDL tPLOH tPLOL tH tPL tS tR tF VOD Timing Input to Output High Delay Input to Output Low Delay Latch Enable to Output High Delay Latch Enable to Output Low Delay Minimum Hold Time Minimum Latch Enable Pulse Width Minimum Setup Time Output Rise Time Output Fall Time Voltage Overdrive Description Propagation delay measured from the time the input signal crosses the reference ( the input offset voltage) to the 50% point of an output low-to-high transition Propagation delay measured from the time the input signal crosses the reference ( the input offset voltage) to the 50% point of an output high-to-low transition Propagation delay measured from the 50% point of the latch enable signal low-to-high transition to the 50% point of an output low-to-high transition Propagation delay measured from the 50% point of the latch enable signal low-to-high transition to the 50% point of an output high-to-low transition Minimum time after the negative transition of the latch enable signal that the input signal must remain unchanged to be acquired and held at the outputs Minimum time the latch enable signal must be high to acquire an input signal change Minimum time before the negative transition of the latch enable signal that an input signal change must be present to be acquired and held at the outputs Amount of time required to transition from a low to a high output as measured at the 20% and 80% points Amount of time required to transition from a high to a low output as measured at the 20% and 80% points Difference between the differential input and reference input voltages
Rev. 0 | Page 10 of 16
04722-016
tPLOL
ADCMP551/ADCMP552/ADCMP553 APPLICATION INFORMATION
The comparators in the ADCMP55x series are very high speed devices. Consequently, high speed design techniques must be employed to achieve the best performance. The most critical aspect of any ADCMP55x design is the use of a low impedance ground plane. A ground plane, as part of a multilayer board, is recommended for proper high speed performance. Using a continuous conductive plane over the surface of the circuit board can create this, allowing breaks in the plane only for necessary signal paths. The ground plane provides a low inductance ground, eliminating any potential differences at different ground points throughout the circuit board caused by ground bounce. A proper ground plane also minimizes the effects of stray capacitance on the circuit board. It is also important to provide bypass capacitors for the power supply in a high speed application. A 1 F electrolytic bypass capacitor should be placed within 0.5 inches of each power supply pin to ground. These capacitors reduce any potential voltage ripples from the power supply. In addition, a 10 nF ceramic capacitor should be placed as close to the power supply pins as possible on the ADCMP55x to ground. These capacitors act as a charge reservoir for the device during high frequency switching. The LATCH ENABLE input is active low (latched). If the latching function is not used, the LATCH ENABLE input pins may be left open. The internal pull-ups on the latch pins set the latch to transparent mode. If the latch is to be used, valid PECL voltages are required on the inputs for proper operation. The PECL voltages should be referenced to VCCI. Occasionally, one of the two comparator stages within the ADCMP551/ADCMP552 is not used. The inputs of the unused comparator should not be allowed to float. The high internal gain may cause the output to oscillate (possibly affecting the comparator that is being used) unless the output is forced into a fixed state. This is easily accomplished by ensuring that the two inputs are at least one diode drop apart, while also appropriately connecting the LATCH ENABLE and LATCH ENABLE inputs as described previously. The best performance is achieved with the use of proper PECL terminations. The open-emitter outputs of the ADCMP55x are designed to be terminated through 50 resistors to VCCO - 2.0 V or any other equivalent PECL termination. If high speed PECL signals must be routed more than a centimeter, microstrip or stripline techniques may be required to ensure proper transition times and prevent output ringing.
CLOCK TIMING RECOVERY
Comparators are often used in digital systems to recover clock timing signals. High speed square waves transmitted over a distance, even tens of centimeters, can become distorted due to stray capacitance and inductance. Poor layout or improper termination can also cause reflections on the transmission line, further distorting the signal waveform. A high speed comparator can be used to recover the distorted waveform while maintaining a minimum of delay.
OPTIMIZING HIGH SPEED PERFORMANCE
As with any high speed comparator amplifier, proper design and layout techniques should be used to ensure optimal performance from the ADCMP55x. The performance limits of high speed circuitry can easily be a result of stray capacitance, improper ground impedance, or other layout issues. Minimizing resistance from source to the input is an important consideration in maximizing the high speed operation of the ADCMP55x. Source resistance in combination with equivalent input capacitance can cause a lagged response at the input, thus delaying the output. The input capacitance of the ADCMP55x, in combination with stray capacitance from an input pin to ground, could result in several picofarads of equivalent capacitance. A combination of 3 k source resistance and 5 pF input capacitance yields a time constant of 15 ns, which is significantly slower than the 500 ps capability of the ADCMP55x. Source impedances should be significantly less than 100 for best performance. Sockets should be avoided due to stray capacitance and inductance. If proper high speed techniques are used, the ADCMP55x should be free from oscillation when the comparator input signal passes through the switching threshold.
COMPARATOR PROPAGATION DELAY DISPERSION
The ADCMP55x has been specifically designed to reduce propagation delay dispersion over an input overdrive range of 20 mV to 1 V. Propagation delay overdrive dispersion is the change in propagation delay that results from a change in the degree of overdrive (how far the switching point is exceeded by the input). The overall result is a higher degree of timing accuracy since the ADCMP55x is far less sensitive to input variations than most comparator designs.
Rev. 0 | Page 11 of 16
ADCMP551/ADCMP552/ADCMP553
Propagation delay dispersion is an important specification in critical timing applications such as ATE, bench instruments, and nuclear instrumentation. Overdrive dispersion is defined as the variation in propagation delay as the input overdrive conditions are changed (Figure 18). For the ADCMP55x, overdrive dispersion is typically 125 ps as the overdrive is changed from 20 mV to 1 V. This specification applies for both positive and negative overdrive since the ADCMP55x has equal delays for positive- and negative-going inputs.
1.5V OVERDRIVE
A current source can also be used with the HYS pin. The relationship between the current applied to the HYS pin and the resulting hysteresis is shown in Figure 16.
-VH 2 0V INPUT 1 +VH 2
INPUT VOLTAGE 20mV OVERDRIVE VREF VOS
0
OUTPUT
04722-017
DISPERSION Q OUTPUT
Figure 19. Comparator Hysteresis Transfer Function
120
Figure 18. Propagation Delay Dispersion
The addition of hysteresis to a comparator is often useful in a noisy environment or where it is not desirable for the comparator to toggle between states when the input signal is at the switching threshold. The transfer function for a comparator with hysteresis is shown in Figure 19. If the input voltage approaches the threshold from the negative direction, the comparator switches from a 0 to a 1 when the input crosses +VH/2. The new switching threshold becomes -VH/2. The comparator remains in a 1 state until the -VH/2 threshold is crossed coming from the positive direction. In this manner, noise centered on 0 V input does not cause the comparator to switch states unless it exceeds the region bounded by VH/2. Positive feedback from the output to the input is often used to produce hysteresis in a comparator (Figure 23). The major problem with this approach is that the amount of hysteresis varies with the output logic levels, resulting in a hysteresis that is not symmetrical around zero. In the ADCMP552, hysteresis is generated through the programmable hysteresis pin. A resistor from the HYS pin to VCCI creates a current into the part that is used to generate hysteresis. Hysteresis generated in this manner is independent of output swing and is symmetrical around the trip point. The hysteresis versus resistance curve is shown in Figure 20.
PROGRAMMED HYSTERESIS (mV)
COMPARATOR HYSTERESIS
100
80
60
40
20
04722-019
0 100
10 RHYS (k)
Figure 20. Comparator Hysteresis Transfer Function
MINIMUM INPUT SLEW RATE REQUIREMENT
As for all high speed comparators, a minimum slew rate must be met to ensure that the device does not oscillate when the input crosses the threshold. This oscillation is due in part to the high input bandwidth of the comparator and the parasitics of the package. Analog Devices recommends a slew rate of 1 V/s or faster to ensure a clean output transition. If slew rates less than 1 V/s are used, hysteresis should be added to reduce the oscillation.
Rev. 0 | Page 12 of 16
04722-018
1
ADCMP551/ADCMP552/ADCMP553 TYPICAL APPLICATION CIRCUITS
VIN VREF
+ ADCMP551/ ADCMP552/ ADCMP553 -
VIN
OUTPUTS
VREF
ADCMP551/ ADCMP552/ ADCMP553 HYS 0 TO 80k
OUTPUTS
04722-020
ALL RESISTORS 50
ALL RESISTORS 50, UNLESS OTHERWISE NOTED
Figure 21. High Speed Sampling Circuits
Figure 23. Adding Hysteresis Using the HYS Control Pin
+VREF VIN
+ ADCMP551/ ADCMP552/ ADCMP553 -
OUTPUTS
VIN
+ ADCMP551/ ADCMP552/ ADCMP553 - 100
50 50 100
50 50
VCCO -2V + ADCMP551/ ADCMP552/ ADCMP553 - OUTPUTS
(VCCO - 2V) x 2
-VREF
Figure 24. How to Interface a PECL Output to an Instrument with a 50 to Ground Input
ALL RESISTORS 50 UNLESS OTHERWISE NOTED
Figure 22. High Speed Window Comparator
04722-021
LATCH ENABLE INPUTS
VCCO -2V
Rev. 0 | Page 13 of 16
04722-024
04722-026
LATCH ENABLE INPUTS
VCCO - 2V
VCCI
VCCO - 2.0V
ADCMP551/ADCMP552/ADCMP553 OUTLINE DIMENSIONS
0.341 BSC
20 11
0.154 BSC
1 10
0.236 BSC
PIN 1
0.065 0.049
0.069 0.053
0.010 0.004 COPLANARITY 0.004
0.025 BSC
0.012 0.008
SEATING PLANE
0.010 0.006
8 0
0.050 0.016
COMPLIANT TO JEDEC STANDARDS MO-137AD
Figure 25. 20-Lead Shrink Small Outline Package [QSOP] (RQ-20) Dimensions shown in inches
0.193 BSC
3.00 BSC
16
9
8
5
0.154 BSC
1 8
3.00 BSC
0.236 BSC
PIN 1
1
4.90 BSC
4
PIN 1 0.065 0.049 0.069 0.053
0.15 0.00
0.65 BSC 1.10 MAX 8 0 0.80 0.60 0.40
0.010 0.025 0.004 BSC COPLANARITY 0.004
0.012 0.008
SEATING PLANE
0.010 0.006
8 0
0.050 0.016
0.38 0.22 COPLANARITY 0.10
0.23 0.08 SEATING PLANE
COMPLIANT TO JEDEC STANDARDS MO-137AB
COMPLIANT TO JEDEC STANDARDS MO-187AA
Figure 26. 16-Lead Shrink Small Outline Package [QSOP] (RQ-16) Dimensions shown in inches
Figure 27. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
ORDERING GUIDE
Model ADCMP551BRQ ADCMP552BRQ ADCMP553BRM EVAL-ADCMP551BRQ EVAL-ADCMP552BRQ Temperature Range -40C to +85C -40C to +85C -40C to +85C Package Description 16-Lead QSOP 20-Lead QSOP 8-Lead MSOP EVALUATION BOARD EVALUATION BOARD Package Option RQ-16 RQ-20 RM-8 Branding
B53
Rev. 0 | Page 14 of 16
ADCMP551/ADCMP552/ADCMP553 NOTES
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ADCMP551/ADCMP552/ADCMP553 NOTES
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04722-0-10/04(0)
Rev. 0 | Page 16 of 16

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