Datasheet EL2357CN, EL2257CS, EL2257CN, EL2357CS Datasheet (ELANT)

Page 1
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C

Features

• Specified for +3V, +5V, or ± 5V Applications
• Power Down to 0 µA
• Output Voltage Clamp
• Large Input Common Mode Range 0V < V
• Output Swings to Ground Without Saturating
• -3 dB Bandwidth = 125 MHz
• ± 0.1 dB Bandwidth = 30 MHz
• Low Supply Current = 5 mA
• Slew Rate = 275 V/µs
• Low Offset Voltage = 4 mV max
• Output Current = ±100 mA
• High Open Loop Gain = 80 dB
• Differential Gain = 0.05%
• Differential Phase = 0.05°
< VS - 1.2V
CM

Applications

• Video Amplifier
• PCMCIA Applications
•A/D Driver
•Line Driver
• Portable Computers
• High Speed Communications
• RGB Printer, FAX, Scanner Applications
• Broadcast Equi pment
• Active Filtering
• Multiplexing

General Description

The EL2257C/EL2357C are supply op amps. Prior si ngle supply op amps have general ly been limite d to bandwid ths and slew rates 1/4 that of the EL2257C /EL2357C. The 125 MHz b andwidth, 2 75 V/µs slew rate, and 0.05%/0.05° differential gain/differential phase makes this part ideal for single or dual supply video speed applications. With its voltage feedback architecture, this amplifier can accept reactive feedback networks, allowing them to be used in analog filtering appli­cations. The inputs can sense signals below the bo ttom supp ly rail and as high as 1.2V below the top rail. Connecting the load resistor to ground and operating fr om a single supply, the output s swing com­pletely to ground without saturating. The outputs can also drive to within 1.2V of the top rail. The EL2257C/EL2357C will output ±100 mA and will operate with single supply voltages as low as 2.7V, making them ideal for portable, low power applications.
The EL2257C/EL2357C have a high speed disable feature. Applying a low logic level to all ENABLE pin s redu ces the supply current to 0 µA within 50 ns. Each amplifier has its own ENABLE pin. This is useful for both multiplexing and reducing power consumption.
The EL2257C/EL2357C also hav e an output v oltage clamp feature. This clamp is a fast recovery (<7 ns) output clamp that pr events the output voltage from going above the preset clamp voltage. This feature is desirable for A/D applications, as A/D converters can require long times to recover if overdriven.
The EL2257C/EL2357C are available in plastic DIP and SOIC pack­ages. Both parts operate over the industrial temperature range of -40°C to +85°C. For single amplifier applications, see the EL2150C/EL2157C. For space saving, industry standard pin out dual and quad applications , see the EL2250C/EL2450C.

Ordering Information

Part No. Temp. Range Package Outline #

EL2257CN -40°C to +85 °C 14 Pin PDIP MDP0031 EL2257CS -40°C to +85°C 14 Pin SOIC MDP0027 EL2357CN -40°C to +85°C 16 Pin PDIP MDP0031 EL2357CS -40°C to +85°C 16 Pin SOIC MDP0027

© 1995 Elantec, Inc.

Connection Diagrams

Top View
January 5, 2000
Top View
Page 2
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Absolute Maximum Ratings (T
Supply Voltage between VS and GND 12.6V Input V oltage (IN+, IN-, EN ABLE, CLAMP) GND–0.3V, V
EL2257C/EL2357C
Differential Input Voltage ±6V Maximum Output Current 90 mA Output Short Circuit Duration (see note
[1]
DC Electrical Characteristics)
= 25 °C)
A
+0.3V
S
Power Dissipation See Curves Storage Temperature Range -65°C to +150°C Ambient Operating Temperature Range -40°C to +85°C Operating Junction Temperature 150°C
Important Note: All parameters having Min/Max specifications are guaranteed. The Test Level column indicates the specific device testing actually performed during
production and Quality inspection. Elantec performs most electrical tests using modern high-speed automatic test equipment, specifically the LTX77 Series system. Unless otherwise noted, all tests are pulsed tests, therefor T
= TC = TA.
J
Test Level Test Procedure
I 100% production tested and QA sample tested per QA test plan QCX0002.
II 100% production tested at T
= 25°C and QA sample tested at TA = 25°C, T
A
MAX
and T
per QA test plan QCX0002.
MIN
III QA sample tested per QA test plan QCX0002. IV Parameter is guaranteed (but not tested) by Design and Characterization Data.
V Parameter is typical value at T
= 25°C for information purposes only.
A
DC Electrical Characteristics
VS=+5V, GND=0V, TA=25°C, VCM=1.5V, V
Parameter Description Test Conditions Min Typ Max
V
OS
TCV
Offset Voltage EL2257C -4 4 I mV
Offset Voltage Temperature Coefficient Measured from Tmin to Tmax 10 V µV/°C
OS
IB Input Bias Current V I
OS
TCI

Input Offset Current VIN=0V -1100 150 +1100 I nA Input Bias Current Temperature Coefficient Measured from Tmin to Tmax 50 V nA/°C

OS
PSRR Power Supply Rejection Ratio V
CMRR Common Mode Rejection Ratio VCM=0V to +3.8V 50 65 I dB
CMIR Common Mode Input Range 0 V R C
R I
S,ON
I
S,OFF
IN IN
OUT
Input Resistance Common Mode 1 2 I M Input Capacitance SOIC Package 1 V pF
Output Resistance Av=+1 40 V m Supply Current - Enabled (per amplifier) VS=V Supply Current - Shut Down (per amplifier) VS=V

PSOR Power Supply Operating Range 2.7 12.0 I V AVOL Open Loop Gain V

OUT
=1.5V, V
CLAMP
=+5V, V
=+5V, unless otherwise specified.
ENABLE
Test
Level Units
EL2357C -6 6 I mV

=0V -5.5 -10 I µA

IN
S=VENABLE
V
CLAMP
=+2.7V to +12V,
=OPEN
45 70 I dB
VCM=0V to +3.0V 55 70 I dB
-1.2 I V
S
PDIP Package 1.5 V pF
=+12V, V
CLAMP
=+10V, V
CLAMP
V
R V V
=+12V, V
S=VCLAMP
=+12V, V
S=VCLAMP
=1 k to GND
L
=+1.5V to +3.5V, RL=1 k to GND 70 V dB
OUT
=+1.5V to +3.5V, RL=150 to GND 60 V dB
OUT
=+12V 5 6.5 I mA
ENABLE
=+0.5V 0 50 I µA
ENABLE
=+0.5V 5 V µA
ENABLE
=+2V to +9V,
OUT
65 80 I dB
2
Page 3
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
DC Electrical Characteristics (Continued)
VS=+5V, GND=0V, TA=25°C, VCM=1.5V, V
Parameter Description Test Conditions Min Typ Max
V
OP
V
ON
I
OUT
I
OUT,OFF
V
IH-EN
V
IL-EN
I
IH-EN
I
IL-EN
V
OR-CL
V
ACC-CL
I
IH-CL
I
IL-CL

Positive Output Voltage Swing VS=+12V, AV=+1, RL=1 kΩ to 0V 10.8 V V

Negative Output Voltage Swing VS=+12V, AV=+1, RL=150 to 0V 5.5 8 I mV
Output Current
[1]
Output Current, Disabled V ENABLE pin Voltage for Power Up Relative to GND Pin 2.0 I V ENABLE pin Voltage for Shut Down Relative to GND Pin 0.5 I V ENABLE pin Input Current-High ENABLE pin Input Current-Low Voltage Clamp Operating Range CLAMP Accuracy
[4]
CLAMP pin Input Current - High VS=V CLAMP pin Input Current - Low / Per
Amplifier
1. Internal short circuit protection circuitry has been built into the EL2257C/EL2357C. See the Applications section.
2. If the disable feature is not desired, tie the ENABLE pins to the V
3. The maximum output voltage that can be clamped is limited to the maximum positive output Voltage, or V inactivates the clamp. If the clamp feature is not desired, either tie the CLAMP pin to the V
4. The clamp accuracy is affected by V
OUT
=1.5V, V
=+5V, V
CLAMP
V

=+12V, AV=+1, RL=150 to 0V 9.6 10.0 I V

S
=±5V, AV=+1, RL=1 kΩ to 0V 4.0 V V
V
S
=±5V, AV=+1, RL=150 to 0V 3.4 3.8 I V
V
S
V

=+3V, AV=+1, RL=150 to 0V 1.8 1.95 I V

S

=±5V, AV=+1, RL=1 k to 0V -4.0 V V

V
S
V

=±5V, AV=+1, RL=150 to 0V -3.7 -3.4 I V

S
=+5V, unless otherwise specified.
ENABLE

VS=±5V, AV=+1, RL=10Ω to 0V ±75 ±100 I mA

=±5V, AV=+1, RL=50 to 0V ±60 V mA
V
S
=+0.5V 0 20 I µA
ENABLE
[2]
[2]
[3]
and RL. See the Typical Curves Section and the Clamp Accuracy vs. VIN and RL curve.
IN
VS=V VS=V
CLAMP CLAMP
=+12V, V =+12V, V
=+12V 340 410 I µA
ENABLE
=+0.5V 0 1 I µA
ENABLE
Relative to GND Pin 1.2 V VIN=+4V, RL=1 k to GND
=+1.5V and +3.5V
V
CLAMP
=+12V 12 25 I µA
CLAMP
VS=+12V, V
S
=+1.2V -30 -15 I µA
CLAMP
pin, or apply a logic high level to the ENABLE pins.
pin, or simply let the CLAMP pin float.
S

-250 100 250 I mV

. Applying a Voltage higher than VOP
OP
OP
EL2257C/EL2357C
Test
Level Units
IV
3
Page 4
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps

Closed Loop AC Electrical Characteristics

VS=+5V, GND=0V, TA=25°C, VCM=+1.5V, V unless otherwise specified
EL2257C/EL2357C
[1]
Parameter Description Test Conditions Min Typ Max
BW -3 dB Bandwidth (Vout=400 mVp-p) V
BW ±0.1 dB Bandwidth (Vout=400 mVp-p) V
GBWP Gain Bandwidth Product V PM Phase Margin R SR Slew Rate V
t
R,tF
Rise Time, Fall Time ±0.1V Step 2.8 V ns OS Overshoot ±0.1V Step 10 V % t
PD
t
S
Propagation Delay ±0.1V step 3.2 V ns
0.1% Settling Time VS=±5V, RL=500, AV=+1, V
0.01% Settling Time V dG Differential Gain dP Differential Phase e
N
i
N
t
DIS
t
EN
t
CL
Input Noise Voltage f=10 kHz 48 V nV/ÐH

Input Noise Current f=10 kHz 1.25 V pA/ÐH

Disable Time Enable Time Clamp Overload Recovery 7Vns
[2]
[2]
[3]
[3]
1. All AC tests are performed on a warmed up part, except slew rate, which is pulse tested.
2. Standard NTSC signal = 286 mVp-p, f=3.58 MHz, as V
3. Disable/Enable time is defined as the time from when the logic signal is applied to the ENABLE pin to when the supply current has reached half its final value.
OUT
=+1.5V, V
CLAMP
=+5V, V
=+5V, AV=+1, RF=0, RL=150 to GND pin,
ENABLE
Test
Level Units
=+5V, AV=+1, RF=0 125 V MHz
S
V
=+5V, AV=-1, RF=500 60 V MHz
S
V
=+5V, AV=+2, RF=500 60 V MHz
S
=+5V, AV=+10, RF=500 6VMHz
V
S
V
=+12V, AV=+1, RF=0 150 V MHz
S
V
=+3V, AV=+1, RF=0 100 V MHz
S
=+12V, AV=+1, RF=0 25 V MHz
S
V
=+5V, AV=+1, RF=0 30 V MHz
S
V
=+3V, AV=+1, RF=0 20 V MHz
S
=+12V, @ AV=+10 60 V MHz
S
=1 kΩ, CL=6 pF 55 V °
L

=+10V, RL=150, Vout=0V to +6V 200 275 I V/µs

S

=+5V, RL=150, Vout=0V to +3V 300 V V/µs

V
S
=±3V 40 V ns
=±5V, RL=500, AV=+1, V
S
OUT
=±3V 75 V ns
OUT

AV=+2, RF=1 k 0.05 V % AV=+2, RF=1 k 0.05 V °

50 V ns 25 V ns
is swept from 0.6V to 1.314V. RL is DC coupled.
IN
z
z
4
Page 5

Typical Performance Curves

Non-Inverting Frequency Response (Gain)
Inverting Frequency Response (Gain)
125 MHz Single Supply, Clamping Op Amps
Non-Inverting Frequency Response (Phase)
Inverting Frequency Response (Phase)
EL2257C/EL2357C
3 dB Bandwidth vs Temperature for Non-Inverting Gains
3 dB Bandwidth vs Temperature for Inverting Gains
EL2257C/EL2357C
Frequency Response for Various R
L
Frequency Response for Various C
L
5
Non-Inverting Frequency Response vs Common Mode Voltage
Page 6
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
3 dB Bandwidth vs Supply Voltage for Non-Inverting Gains
3 dB Bandwidth vs Supply Voltage for Inverting Gains
Frequency Response for Various Supply Voltages, A
= + 1
V
Frequency Response for Various Supply Voltages,
= + 2
A
V
PSSR and CMRR vs Frequency
PSRR and CMRR vs Die Temperature
Open Loop Gain and Phase vs Frequency
Open Loop Voltage Gain vs Die Temperature
6
Closed Loop Output Impedance vs Frequency
Page 7
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
Large Signal Step Response, V
= +3V
S
Small Signal Step Response
Large Signal Step Response, VS = +5V
Large Signal Step Response,
= ±5V
V
S
Large Signal Step Response, VS = +12V
Slew Rate vs Temperature
Settling Time vs Settling Accuracy
Voltage and Current Noise vs Frequency
7
Page 8
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
Differential Gai n fo r Single Supply Operation
2nd and 3rd Harmonic Distortion vs Frequency
Differential Phase for Single Supply Operation
2nd and 3rd Harmonic Distortion vs Frequency
Differential Gain and Phase for Dual Supply Operation
2nd and 3rd Harmonic Distortion vs Frequency
Output Voltage Swing vs Frequency for THD < 0.1%
Output Voltage Swing vs Frequency for Unlimited Distortion
8
Output Current vs Die Temperature
Page 9
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
Supply Current vs Supply Voltage (per amplifier)
Offset Voltage vs Die Temperature (4 Samples)
Supply Current vs Die Temperature (per amplifier)
Input Bias Cur r ent vs Input Voltage
Input Resistance vs Die Temperature
Input Offset Current and Input Bias Current vs Die Temperature
Positive Output Voltage Swing vs Die Temperature, RL = 150 to GND
Negative Output Voltage Swing vs Die Temperature, RL = 150 to GND
9
Clamp Accuracy vs Die Temperature
Page 10
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
IClamp Accuracy R
= 150
L
Enable Resp onse for a Family of DC Inputs
Clamp Accuracy RL = 1 k
Disable Response for a Family of DC Inputs
Clamp Accuracy RL = 10 k
Disable/Enable Response for a Family of Sine Waves
OFF Isolation
10
Page 11
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
EL2257 Channel to Channel Isolation vs Frequency
14-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature
EL2357 Channel to Channel Isolation vs Frequency
16-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature
14-Lead Plastic SO Maximum Power Dissipation vs Ambient Temperature
16-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature
11
Page 12
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps

Simplified Schematic (One Channel)

EL2257C/EL2357C
12
Page 13

Applications Information

EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Product Description
The EL2257C/EL2357C’s, connected in voltage fol- lower mode, -3 dB bandwidth is 125 MHz while maintaining a 275 V/µs slew rate. Wit h an input a nd out­put common mode ra nge that include s ground, thes e amplifiers were optimized for single supply operation, but will also accept dual supplies. They operate on a total supply voltage range as low as +2.7V or up to +12V. This makes them ideal for +3V applications, especially portable computers.
While many amplifiers claim to operate on a single sup­ply, and some can sense ground at their inputs, most fail to truly drive their outputs to gro und. If they do succeed in driving to ground, the amplifier often saturates, caus­ing distortion and recovery delays. However , special circuitry built into the EL2257C/EL2357C allows the output to follow the input signal to ground without recovery delays.
Power Supply Bypassing And Printed Circuit Board Layout
As with any high-frequency device, good printed circuit board layout is necessary for optimum performance. Ground plane constructio n is highly recommended. Lead lengths should be as short as possible. The power supply pins must be well bypassed to reduce the risk of oscillation. The combi nation o f a 4.7 µF tantalum capac­itor in parallel with a 0.1 µF ceramic capacitor has been shown to work well when placed at each supply pin. For single supply operation, where the GND pin is con­nected to the ground plane, a single 4.7 µF tantalum capacitor in parallel with a 0.1 µF ceramic capacitor from the V
For good AC performance, parasiti c capacita nce should be kept to a minimum. Ground plane construction should be used. Carbon or Metal-Film resistors a re acceptable with the Metal-Film resistors giving slightly less peaking and bandwidth because of their additional series inductance. Use of sockets, particularly for the SO package should b e avoi ded if possi ble. Soc kets add par­asitic inductance and capacitance which will result in some additional peaking and ove rsho ot.
pin to the GND pin will suffice.
S+
Supply Voltage Range and Single-Supply Operation
The EL2257C/EL2357C have been designed to operate with supply voltages ha vi ng a span of greater tha n 2. 7V, and less than 12V. In practical terms, this means that the EL2257C/EL2357C will operate on dual supplies rang­ing from ±1.35V to ±6V. With a single- supply, the EL2257C/EL2357C will operat e from +2.7V to +12V. Performance has been optimized f or a single +5V supply.
Pins 11 and 4 (14 and 3) are the power supply pins on the EL2257C (EL2357C). The positive power supply is connected to pin 11 (14). When used in single supply mode, pin 4 (3) is connected to ground. When used in dual supply mode, the negati ve power supply is con­nected to pin 4 (3).
As supply voltages continue to decrease , it becomes nec­essary to provide input and output voltage ranges that can get as close as possible to the supply voltages. The EL2257C/EL2357C ha ve an input voltage rang e that includes the negative supply and extends to within 1.2V of the positive suppl y . So, for e xam pl e, on a si ngle +5V supply, the EL2257C/EL2357C have an input range which spans from 0V to 3.8V.
The output range o f the EL 22 57C/EL 2357 C is a lso q uite large. It includes the negative rail, and extends to within 1V of the top supply rail with a 1 k load. On a +5V supply, the output is therefore capable of swi nging from 0V to +4V. On split supplies, t he outp ut will swing ±4V. If the load resistor is tied to the negative rail and split supplies are used, the output range is extended to the negative rail.
Choice Of Feedback Resistor, R
The feedback resistor forms a pole with the input capac­itance. As this pole becomes larger, phase margin is reduced. This increases ringing in the time domain and peaking in the frequency domain. Therefore, R some maximum value which should not be exceeded for optimum performance. If a large value of R used, a small capacitor in the few picofarad range in par­allel with RF can help to reduce this ringin g a nd pe a king at the expense of reducing the bandwidth.
F
has
F
must be
F
13
Page 14
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
As far as the output stage of the amplifier is concerned,
+ RG appear in parallel with RL for gains other than
R
F
+1. As this combination gets smaller, the bandwidth
EL2257C/EL2357C
falls off. Consequently, R should not be exceeded for op timum performance.
= +1, RF = 0 is optimum. For AV = -1 or +2
For A
V
(noise gain of 2), optimu m r esponse is obt ain ed wit h R between 500 and 1 k. For AV = -4 or +5 (noise gain of 5), keep R
between 2 k and 10 kΩ.
F
has a minimum value that
F
Video Performance
For good video performance, an amplifier is required to maintain the same output impedance and the same fre­quency response as DC level s are changed at the output. This can be difficul t when d riv ing a stan dar d vide o load of 150, because of the change in output curre nt with DC level. Differential Gain and Differential Phase for the EL2257C/EL2357C are specified with the black level of the output vide o signal se t to +1.2V. This al lows ample room for the sync pulse even in a ga in of +2 con ­figuration. This results in dG and dP specifications of
0.05% and 0.05° while driving 150 at a gain of +2. Setting the black level to other values, although accept­able, will compromise peak performance. For example, looking at the single supply dG and dP curves for
=150, if the output black level clamp is reduced
R
L
from 1.2V to 0.6V dG/dP will increase from
0.05%/0.05° to 0.08%/0.25°. Note that in a gain of +2 configuration, this is the lowest black leve l allowed such that the sync tip doesnt go below 0V.
If your application requires that the output goes to ground, then the output stage of the EL2257C/EL2357C, like all other single supply op amps, requires an external pull down resistor tied to ground. As mentioned above, the current flowing through this resistor become s the DC bias current for the output st age NPN tran sistor. As this current approaches zero, the NPN turns off, and dG and dP will increase. This becomes more critical as the load resistor is increased in value. While driving a light load, such as 1 k, if the input black level is kept above
1.25V, dG and dP are a respectable 0.03% and 0.03°. For other biasing conditions see the Differential Gain
and Differential Phase vs. Input Voltage curves.
Output Drive Capability
In spite of their moderately low 5 mA of supply current, the EL2257C/EL2357C are capable o f providing ±100 mA of output current into a 10 l oad, or ±60 mA into 50. With this large output current capability, a 50 load can be driven to ±3V with V excellent choice for driving isolation transformers in
F
telecommunications applications.
= ±5V, making it an
S
Driving Cables and Capacitive Loads
When used as a cable driver, double termination is always recommended for reflection-free perfor mance. For those applications, the back-te rm ina ti on series re sis­tor will de-coup le the EL2257C/E L2357C from the cable and allow extensive capacitive drive. Howe ver, other applications may have high capacitive loads with­out a back-termination resistor. In these applications, a small series resistor (usually between 5 and 50) can be placed in series with th e output to eliminate most peaking. The gain resistor (R make up for any gain loss which may be created by this additional resistor at the output.
) can then be chosen to
G
Disable/Power-Down
Each amplifier in the EL2257 C/EL2357C can be ind i­vidually disabled, placing each output in a high­impedance state. The dis able or enable action takes only about 40 ns. When all amplifiers are disabled, the total supply current is reduced to 0 mA, thereby eliminating all power consumption by the EL2257C/EL2357C. The EL2257C/EL2357C amplifiers power down can be controlled by st andard CMOS sign al levels at ea ch ENABLE pin. The applied CMOS signal is relative to the GND pin. For example, if a single +5V supply is used, the logic voltage levels will be +0.5V and +2.0V. If using dual ±5V supplies, the logic leve ls will be -4.5V and -3.0V. Letting all ENABLE pin s float will disable the EL2257C/EL2357C. If the power-down feature is not desired, connect all ENABLE pins to th e V The guaranteed logic leve ls of +0 .5V an d +2. 0V are no t standard TTL levels of +0.8V and +2.0V, so care must be taken if standard TTL will be used to drive the ENABLE pins.
S+
pin.
14
Page 15
Output Voltage Clamp
The EL2257C/EL2357C amplifiers have an output volt­age clamp. This clamping acti on is fast, bei ng act ivated almost instantaneously, and being deactivated in < 7 ns, and prevents the output voltage from going above the preset clamp voltage. This can be very helpful when the EL2257C/EL2357C are used to drive an A/D converter, as some converters can require long times to recover if overdriven. The output voltag e remains at the clamp voltage level as long as the product of the input voltage and the gain setting exceeds the clamp voltage. For example, if the EL2257C/EL2357C is connected in a gain of 2, and +3V DC is appl ied to the CLAM P pin, an y voltage higher than +1.5V at the inputs will be clamped and +3V will be seen at the output. Each amplifier of the EL2257C have their own CLAMP pin, so individual clamp levels may be set, whereas a single CLAMP pin controls the cl amp level of the EL2357C .
Figure 1 below is the EL2257C with each amplifier unity gain connected. Amplifie r A is b eing d rive n by a 3 Vp-p sinewave and has 2.25V applied to CLAMPA, while amplifier B is driven by a 3 Vp-p triangle wave and 1.5V is applied to CLAMPB. The resulti ng output waveforms, with their outputs being clamped is shown in Figure 2.
EL2257C/EL2357C
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps

Figure 2.

Figure 3 shows the output of amplifier A of the same circuit being driven by a 0.5V to 2.75V square wave as the clamp voltage is varied from 1.0V to 2.5V, as well as the unclamped output signa l. The risi ng edge of the sig­nal is clamped to the vol tage ap plied to th e CLAMP pin almost instantaneously. The output recovers from the clamped mode with in 5–7 ns, depending on the clamp voltage. Even when the CLAMP pin is taken 0.2V below the minimum 1.2V specified, the output is still clamped and recovers in about 11 ns.

Figure 1.

Figure 3.

The clamp accuracy is affected by 1) the CLAMP pin voltage, 2) the input voltage, and 3) the load resistor. Depending upon the application, the accuracy may be as little as a few tens of millivolts up to a few hundred mil­livolts. Be sure to allow for these inaccuracies when choosing the clamp vo ltage. Curves of Clam p A ccu racy vs. V the Typical Performance Curves Section.
15
and VIN for 3 values of RL are included in
CLAMP
Page 16
EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
Unlike amplifiers that clamp at the input and are there­fore limited to non-inverting applications only, the EL2257C/EL2357C outp ut cl am p arc hite ctur e work s f or
EL2257C/EL2357C
both inverting and non-inverting gain applications. There is also no maximum voltage difference limitation between V clamped architectures.
The voltage clamp operates for any voltage between +1.2V above the GND pin, and the minimum o utput voltage swing, V below +1.2V can saturate transistors and should there­fore be avoided. Forcing the CLAMP pin abov e V simply de-activates the CLAMP feature. In other words, one cannot expect to clamp any voltage higher than what the EL2257C/EL2357C can drive to in the first p lace. If the clamp feature is not desired, either let the CLAMP pin float or connect it to the VS+ pin.
and V
IN
OP
which is common on input
CLAMP
. Forcing the CLAMP pin much
EL2257C/EL2357C Comparator Application
The EL2257C/EL2357C can be used as a very fast, sin­gle supply comparator by utilizing the clamp feature. Most op amps used as comparators allow only slow speed operation because of output saturation issues. However, by applying a DC voltage to the CLAMP pin of the EL2257C/EL2 357 C, the ma xim um outpu t volta ge can be clamped, thus preventing saturation. Figure 4 is amplifier A of an EL22 57C i mpl eme nted as a co mpar a­tor. 2.25V DC is applied to the CLAMP pin, as well as the IN- pin. A differential signal is then applied between the inputs. Figure 5 shows the output square wave that results when a ±1V, 10 MHz triangular wave is applied,
while Figure 6 is a graph of propag at io n de lay vs. ove r­drive as a square wave is presented at t he input.
OP

Figure 4.

Figure 5.

Propagation Delay vs Overdrive EL2257/EL2357 as a Comparator

Figure 6.

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EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
Video Sync Pulse Remover Application
All CMOS Analog to Digital Converters (A/Ds) have a parasitic latch-up problem when subjected to negative input voltage levels. Since the sync tip contains no use­ful video information and it is a negative go ing pulse, we can chop it off. Figure 7 shows a unity gain connected amplifier A of an EL2257C. Figure 8 shows the com­plete input video signal applied at the input, as well as the output signal with the negative going sync pulse removed.

Figure 7.

inputs. Logic signals are applied to each of the ENABLE pins to cycle through turning each of the amplifiers on, one at a time. Figure 10 shows the resulting output waveform at V ns. Notice the outputs are tied directly together. Decou­pling resistors at each output are not necessary. In fact, adding them approximately doubles the switching time to 100 ns.
. Switching is complete in about 50
OUT

Figure 9.

Figure 8.

Multiplexing with the EL2257C/EL2357C
The ENABLE pins on the EL2257C/EL2 35 7C a llo w for multiplexing applications. Figure 9 shows an EL2357C with all 3 outputs tied together, driving a back termi­nated 75 video load. Three sinewaves of varying amplitudes and frequencies are app lied to the three

Figure 10.

Short Circuit Current Limit
The EL2257C/EL2357C have internal short circuit pro­tection circuitry that protect it in the event of its output being shorted to either supply rail. This limit is set to around 100 mA nominally and reduces with increasing junction temperature. It is intended to handle temporary shorts. If an output is shorted indefinitely, the power dis­sipation could easily increase such that the part will be destroyed. Maximum reliability is maintained if the out­put current never exceeds ±90 mA. A heat sink may be
17
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EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
required to keep the junction temperature below abso­lute maximum when an output is shorted indefinite ly.
EL2257C/EL2357C
Power Dissipation
With the high output drive capability of the EL2257C/EL2357C, it is possible to exceed the 150°C Absolute Maximum junction temperature under certain load current conditions. Therefore, it is important to cal­culate the maximum junction temperature for the application to determine if power-supply voltages, load conditions, or package type need to be modified for the EL2257C/EL2357C to rema in in the safe op er ating area .
The maximum power dissipation allowed in a package is determined by:
T
PD
MAX
JMAXTAMAX
----------------------------------------------=
θ
JA
where:
T
T
θ
PD
= Maximum Junction Temperature
JMAX
= Maximum Ambient Temperature
AMAX
= Thermal Resistance of the Package
JA
= Maximum Power Dissipatio n in the
MAX
Package.
The maximum power dissipation actuall y produced by an IC is the total quiescent supply current times the total power supply voltage, plus th e power in the IC d ue to the load, or:
V
PD
MAX
NVSI
SMAXVSVOUT
()
--------------- -
×+××=
where:
N = Number of amplifiers = T ot al Supply Voltage
V
S
I
V
= Maximum Supply Current per amplifier
SMAX
= Maximum Output Voltage of the Application
OUT
RL = Load Resistance tied to Ground
If we set the two PD each other, and solve for V
equations, [1] and [2], equal to
MAX
, we can get a family of
S
OUT
R
L
curves for various loads and output voltages according to:
RLT
---------------------------------------------------------------- -V
-----------------------------------------------------------------------------------------------=
V
S
()×
JMAXTAMAX
N θ
×
JA
×()V
+
I
SRL
()
+
OUT
OUT
2
Figures 11 and 12 below show total single supply volt-
vs. RL for various output voltage swings for the
age V
S
PDIP and SOIC packages. The curves assu me WORST CASE conditions of TA = +85°C and IS = 6.5 mA per amplifier.
EL2257 Single Supply Voltage vs. R
for Various
Load
V
and Packages
OUT

Figure 11.

EL2357 Single Supply Voltage vs. R
for Various
Load
V
and Packages
OUT

Figure 12.

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125 MHz Single Supply, Clamping Op Amps

EL2257C/EL2357C Macromodel (one channel)

* Revision A, October 1995 * Pin numbers reflect a standard single opamp. * When not being used, the clamp pin, pin 1, * should be connected to Vsupply, pin 7 * Connections: +input * | -input * | | +Vsupply * | | | -Vsupply * | | | | output * | | | | | clamp * | | | | | | .subckt EL2257/el 3 2 7 4 6 1 * * Input Stage * i1 7 10 250µA i2 7 11 250µA r1 10 11 4K q1 12 2 10 qp q2 13 3 11 qpa r2 12 4 100 r3 13 4 100 * * Second Stage & Compensation * gm 15 4 13 12 4.6m r4 15 4 15Meg c1 15 4 0.36pF * * Poles * e1 17 4 15 4 1.0 r6 17 25 400 c3 25 4 1pF r7 25 18 500 c4 18 4 1pF * * Connections:IN+IN+IN+IN+IN+IN+IN+INININININ * Output Stage & Clamp * i3 20 4 1.0mA q3 7 23 20 qn q4 7 18 19 qn q5 7 18 21 qn q6 4 20 22 qp q7 7 23 18 qn d1 19 20 da d2 18 1 da r8 21 6 2 r9 22 6 2 r10 18 21 10k r11 7 23 100k d3 23 24 da d4 24 4 da d5 23 18 da * * Power Supply Current * ips 7 4 3.2mA * * Models *
EL2257C/EL2357C
EL2257C/EL2357C
19
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EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
.model qn npn(is800e-18 bf150 tf0.02nS) .model qpa pnp(is810e-18 bf50 tf0.02nS) .model qp pnp(is800e-18 bf54 tf0.02nS) .model da d(tt0nS)
EL2257C/EL2357C

.ends

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EL2257C/EL2357C
125 MHz Single Supply, Clamping Op Amps
EL2257C/EL2357C
General Disclaimer
Specifications contained in this data sheet are in effect as of the publicat ion date shown. Elantec, Inc. re serves the r ight to make changes in th e cir­cuitry or specifications cont ained herein at a ny time without notice. Elante c, Inc. assumes no res ponsibili ty for t he us e of any circuits described herein and makes no representations that they are free from patent infringement.
WARNING - Life Supp ort Policy
Elantec, Inc. products are not authorized for and should not be used within Life Support Systems without the specific written consent of Elantec, Inc. Life Support systems are equipment intend ed to sup-
Elantec, Inc.
1996 Tarob Court Milpitas, CA 95035 Telephone: (408) 945-1323
(800) 333-6314 Fax: (408) 945-9305 European Office: 44-71-482-4596
port or sustain life and whose failure to perform when properly used in accordance with instructions provided can be reasonably expected to result in significant personal injury or death. Users con­templating applicatio n of Elantec, In c. Products in Li fe Support Systems are requested to contact Elantec, Inc. factory headquarters to establish suitable terms & conditions for these applications. Elan­tec, Inc. s warranty is limited to replacement of defective components and does not cov er injury to per sons or prop erty or other consequential damages.
January 5, 2000
21
Printed in U.S.A.
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