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Single-Supply, High Speed, Triple Op Amp with Charge Pump ADA4858-3
FEATURES
Integrated charge pump Supply range: 3 V to 5.5 V Output range: -3.3 V to -1.8 V 50 mA maximum output current for external use at -3 V High speed amplifiers -3 dB bandwidth: 600 MHz Slew rate: 600 V/s 0.1 dB flatness: 85 MHz 0.1% settling time: 18 ns Low power Total quiescent current: 42 mA Power-down feature High input common-mode voltage range -1.8 V to +3.8 V at +5 V supply Current feedback architecture Differential gain error: 0.01% Differential phase error: 0.02 Available in 16-lead LFCSP
CONNECTION DIAGRAM
ADA4858-3
OUT1 +IN1 -IN1 NC 13
16
15 14
+VS 1 C1_a 2 C1_b 3 CPO 4 CHARGE PUMP
12 +IN2 11 -IN2 10 OUT2 9 PD
5 +VS
6 +IN3
7 -IN3
8 OUT3
Figure 1.
APPLICATIONS
Professional video Consumer video Imaging Active filters
GENERAL DESCRIPTION
The ADA4858-3 (triple) is a single-supply, high speed current feedback amplifier with an integrated charge pump that eliminates the need for negative supplies in order to output negative voltages or output a 0 V level for video applications. The 600 MHz -3 dB bandwidth and 600 V/s slew rate make this amplifier well suited for many high speed applications. In addition, its 0.1 dB flatness out to 85 MHz at G = 2, along with its differential gain and phase errors of 0.01% and 0.02 into a 150 load, make it well suited for professional and consumer video applications.
This triple operational amplifier is designed to operate on supply voltages of 3.3 V to 5 V, using only 42 mA of total quiescent current, including the charge pump. To further reduce the power consumption, it is equipped with a powerdown feature that lowers the total supply current to as low as 2.5 mA when the amplifier is not being used. Even in powerdown mode, the charge pump can be used to power external components. The maximum output current for external use is 50 mA at -3 V. The amplifier also has a wide input commonmode voltage range that extends from 1.8 V below ground to 1.2 V below the positive rail at a 5 V supply. The ADA4858-3 is available in a 16-lead LFCSP, and it is designed to work over the extended industrial temperature range of -40C to +105C.
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: 781.461.3113 (c)2008 Analog Devices, Inc. All rights reserved.
07714-001
NOTES 1. NC = NO CONNECT. 2. EXPOSED PAD, CONNECT TO GROUND.
ADA4858-3 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 Connection Diagram ....................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Maximum Power Dissipation ..................................................... 5 ESD Caution .................................................................................. 5 Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 13 Overview ..................................................................................... 13 Charge Pump Operation ........................................................... 13 Applications Information .............................................................. 14 Gain Configurations .................................................................. 14 DC-Coupled Video Signal ........................................................ 14 Multiple Video Driver................................................................ 14 PD (Power-Down) Pin .............................................................. 15 Power Supply Bypassing ............................................................ 15 Layout .......................................................................................... 15 Outline Dimensions ....................................................................... 16 Ordering Guide .......................................................................... 16
REVISION HISTORY
10/08--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADA4858-3 SPECIFICATIONS
TA = 25C, VS = 5 V, G = 2, RF = 301 , RF = 402 for G = 1, RL = 150 , unless otherwise noted. Table 1.
Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Conditions VOUT = 0.1 V p-p, G = 1 VOUT = 0.1 V p-p VOUT = 2 V p-p, G = 1 VOUT = 2 V p-p VOUT = 2 V p-p VOUT = 2 V step VOUT = 2 V step fC = 1 MHz, VO = 2 V p-p fC = 5 MHz, VO = 2 V p-p f = 5 MHz f = 1 MHz f = 1 MHz (+IN/-IN) Min Typ 600 350 165 175 85 600 18 -86/-94 -71/-84 -60 4 2/9 0.01 0.02 -14 -2 -13 300 +IN -IN +IN Typical +0.5 +0.7 +8 390 15 90 1.5 -1.8 -61 -1.4 to +3.6 Rise/fall, f = 5 MHz fC = 1 MHz, HD2 -50 dBc Enabled Powered down -0.1 0.3 1.6 3 15 19 23 0.25 4 -64 -58 -3 5.5 21 -1.7 to +3.7 15 21 1.9 2 +0.1 +3.8 -54 +14 +2 +13 Max Unit MHz MHz MHz MHz MHz V/s ns dBc dBc dB nV/Hz pA/Hz % Degrees mV A A k M pF V dB V ns mA V V A s s V mA mA mA mA dB dB V mA
Bandwidth for 0.1 dB Flatness Slew Rate Settling Time to 0.1% NOISE/DISTORTION PERFORMANCE Harmonic Distortion (HD2/HD3) Crosstalk Input Voltage Noise Input Current Noise Differential Gain Error Differential Phase Error DC PERFORMANCE Input Offset Voltage + nput Bias Current -Input Bias Current Open-Loop Transimpedance INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Output Voltage Swing Output Overdrive Recovery Time Maximum Linear Output Current @ VO = 1 VPEAK POWER-DOWN Input Voltage Bias Current Turn-On Time Turn-Off Time POWER SUPPLY Operating Range Total Quiescent Current Amplifiers Charge Pump Total Quiescent Current When Powered Down Amplifiers Charge Pump Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Charge Pump Output Voltage Charge Pump Sink Current
0.15
0.3 -60 -54 -2.5 150
-3.3
Rev. 0 | Page 3 of 16
ADA4858-3
TA = 25C, VS = 3.3 V, G = 2, RF = 301 , RF = 402 for G = 1, RL = 150 , unless otherwise noted. Table 2.
Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Conditions VOUT = 0.1 V p-p, G = 1 VOUT = 0.1 V p-p VOUT = 2 V p-p, G = 1 VOUT = 2 V p-p VOUT = 2 V p-p VOUT = 2 V step VOUT = 2 V step fC = 1 MHz, VO = 2 V p-p fC = 5 MHz, VO = 2 V p-p f = 5 MHz f = 1 MHz f = 1 MHz (+IN/-IN) Min Typ 540 340 140 145 70 430 20 -88/-91 -75/-78 -60 4 2/9 0.02 0.03 -14 -2 -13 300 +IN -IN +IN Typical +0.7 +0.6 +7 350 15 90 1.5 -0.9 -60 -0.6 to +2.1 Rise/fall, f = 5 MHz fC = 1 MHz, HD2 -50 dBc Enabled Powered down -0.1 0.3 1.6 3 14 19 21 0.25 2 -63 -57 -2 5.5 20 -0.9 to +2.2 15 20 1.25 1.35 +0.1 +2.2 -54 +14 +2 +13 Max Unit MHz MHz MHz MHz MHz V/s ns dBc dBc dB nV/Hz pA/Hz % Degrees mV A A k M pF V dB V ns mA V V A s s V mA mA mA mA dB dB V mA
Bandwidth for 0.1 dB Flatness Slew Rate Settling Time to 0.1% NOISE/DISTORTION PERFORMANCE Harmonic Distortion (HD2/HD3) Crosstalk Input Voltage Noise Input Current Noise Differential Gain Error Differential Phase Error DC PERFORMANCE Input Offset Voltage +Input Bias Current -Input Bias Current Open-Loop Transimpedance INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Output Voltage Swing Output Overdrive Recovery Time Maximum Linear Output Current @ VO = 1 VPEAK POWER-DOWN Input Voltage Bias Current Turn-On Time Turn-Off Time POWER SUPPLY Operating Range Total Quiescent Current Amplifiers Charge Pump Total Quiescent Current When Powered Down Amplifiers Charge Pump Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Charge Pump Output Voltage Charge Pump Sink Current
0.15
0.3 -60 -54 -1.8 45
-2.1
Rev. 0 | Page 4 of 16
ADA4858-3 ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Supply Voltage Internal Power Dissipation1 16-Lead LFCSP Input Voltage (Common Mode) Differential Input Voltage Output Short-Circuit Duration Storage Temperature Range Operating Temperature Range Lead Temperature (Soldering, 10 sec)
1
MAXIMUM POWER DISSIPATION
Rating 6V See Figure 2 (-VS - 0.2 V) to (+VS - 1.2 V) VS Observe Power Derating Curves -65C to +125C -40C to +105C 300C
The maximum power that can be safely dissipated by the ADA4858-3 is limited by the associated rise in junction temperature. The maximum safe junction temperature for plastic encapsulated devices is determined by the glass transition temperature of the plastic, approximately 150C. Temporarily exceeding this limit may cause a shift in parametric performance due to a change in the stresses exerted on the die by the package. Exceeding a junction temperature of 175C for an extended period can result in device failure. To ensure proper operation, it is necessary to observe the maximum power derating curves in Figure 2.
2.5
Specification is for device in free air.
MAXIMUM POWER DISSIPATION (W)
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 section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
2.0
1.5
1.0
0.5
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE (C)
Figure 2. Maximum Power Dissipation vs. Temperature for ADA4858-3
ESD CAUTION
Rev. 0 | Page 5 of 16
07714-002
0 -40
ADA4858-3 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
ADA4858-3
TOP VIEW (Not to Scale)
OUT1
+IN1
-IN1
16
15 14
13
NC
+VS 1 C1_a 2 C1_b 3 CPO 4 CHARGE PUMP
12 +IN2 11 -IN2 10 OUT2 9 PD
5
6
7
8
OUT3
+IN3
+VS
-IN3
NOTES 1. NC = NO CONNECT. 2. EXPOSED PAD, CONNECT TO GROUND.
Figure 3. Pin Configuration.
Table 4. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 (EPAD) Mnemonic +VS C1_a C1_b CPO +VS +IN3 -IN3 OUT3 PD OUT2 -IN2 +IN2 NC +IN1 -IN1 OUT1 Exposed Pad (EPAD) Description Positive Supply for Charge Pump. Charge Pump Capacitor Side a. Charge Pump Capacitor Side b. Charge Pump Output. Positive Supply. Noninverting Input 3. Inverting Input 3. Output 3. Power Down. Output 2. Inverting Input 2. Noninverting Input 2. No Connect. Noninverting Input 1. Inverting Input 1. Output 1. The exposed pad must be connected to ground.
Rev. 0 | Page 6 of 16
07714-003
ADA4858-3 TYPICAL PERFORMANCE CHARACTERISTICS
VS = 5 V, G = 2, RF = 301 , RF = 402 for G = 1, RF = 200 for G = 5, RL = 150 , large signal VOUT = 2 V p-p, small signal VOUT = 0.1 V p-p, and T = 25C, unless otherwise noted.
2 2 G=1 G=2 1 0 -1 -2 -3 -4 -5 -6 -7
07714-004
NORMALIZED CLOSED-LOOP GAIN (dB)
NORMALIZED CLOSED-LOOP GAIN (dB)
1 0 -1 -2 -3 -4 -5 -6 -7 1 10
G=1
G=2 G=5
G=5
1
10
100
1000
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 4. Small Signal Frequency Response vs. Gain
2 2 G=1
Figure 7. Large Signal Frequency Response vs. Gain
VS = 3.3V
VS = 3.3V G=1
NORMALIZED CLOSED-LOOP GAIN (dB)
0 -1 -2 -3 -4 -5 -6 -7 G=5
G=2
NORMALIZED CLOSED-LOOP GAIN (dB)
1
1 0 -1 -2 -3 -4 -5 -6 -7 1 10 100 1000
07714-008 07714-009
G=2
G=5
1
10
100
1000
FREQUENCY (MHz)
07714-005
-8
-8 FREQUENCY (MHz)
Figure 5. Small Signal Frequency Response vs. Gain
2 2 RF = 301
Figure 8. Large Signal Frequency Response vs. Gain
NORMALIZED CLOSED-LOOP GAIN (dB)
NORMALIZED CLOSED-LOOP GAIN (dB)
1 0 -1 -2 -3 -4 -5 -6 -7 1 10
1 0 -1 -2 -3 -4 -5 -6 -7 -8 1 10 RF = 402 RF = 499
RF = 200
RF = 200 RF = 301
RF = 402 RF = 499
100
1000
07714-006
-8 FREQUENCY (MHz)
100
1000
FREQUENCY (MHz)
Figure 6. Small Signal Frequency Response vs. Feedback Resistor
Figure 9. Large Signal Frequency Response vs. Feedback Resistor
Rev. 0 | Page 7 of 16
07714-007
-8
-8
ADA4858-3
0.2
0.2
NORMALIZED CLOSED-LOOP GAIN (dB)
NORMALIZED CLOSED-LOOP GAIN (dB)
0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7
07714-010
0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 1 10
RF = 200
VS = 5V
RF = 301
VS = 3.3V
1
10
100
1000
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 10. Large Signal 0.1 dB Flatness vs. Supply Voltage
0 -10 -20
DISTORTION (dBc) DISTORTION (dBc)
Figure 13. Large Signal 0.1 dB Flatness vs. Feedback Resistor
0 -10 -20 -30 -40 -50 -60 -70 -80 -90
07714-011
-30 -40 -50 -60 -70 -80 -90 -100 1 10 FREQUENCY (MHz) 100 HD3 HD2
HD2
HD3
1
10 FREQUENCY (MHz)
100
Figure 11. Harmonic Distortion vs. Frequency
10 0 -10 -20 -30 -40 -50 -60 -70 0.1
Figure 14. Harmonic Distortion vs. Frequency, VS = 3.3 V
-10
-20
-30
CMRR (dB)
PSRR (dB)
-40
-50
-60
07714-012
1
10 FREQUENCY (MHz)
100
400
1
10 FREQUENCY (MHz)
100
400
Figure 12. Power Supply Rejection Ratio (PSRR) vs. Frequency
Figure 15. Common-Mode Rejection Ratio (CMRR) vs. Frequency
Rev. 0 | Page 8 of 16
07714-015
-70 0.1
07714-014
-100
07714-013
-0.8
-0.8
ADA4858-3
-30 -40
FORWARD ISOLATION (dB)
-20 -30 -40
CROSSTALK (dB)
07714-016
-50 -60 -70 -80 -90 -100 0.1
-50 -60 -70 -80 -90 0.1
1
10 FREQUENCY (MHz)
100
400
1
10 FREQUENCY (MHz)
100
400
Figure 16. Forward Isolation vs. Frequency
0.15
1.5
Figure 19. Crosstalk vs. Frequency
2.0
VOUT = 200mV p-p
0.05
0.5
1.0
0
0
0.5
-0.05 VS = 5V -0.10
07714-017
-0.5 VS = 3.3V -1.0 VS = 5V -1.5 TIME (5ns/DIV)
0
-0.5
-0.15
-1.0
TIME (5ns/DIV)
Figure 17. Small Signal Transient Response vs. Supply Voltage
0.15
Figure 20. Large Signal Transient Response vs. Supply Voltage
1.5
G=1 VOUT = 200mV p-p 1.0
OUTPUT VOLTAGE (V)
CL = 4pF C = 10pF L
0.10
OUTPUT VOLTAGE (V)
CL = 6pF 0.5
0.05
0
0
-0.05 CL = 4pF -0.10
07714-018
-0.5
-1.0
07714-021
-0.15
CL = 10pF
CL = 6pF
-1.5
G=1 TIME (5ns/DIV)
TIME (5ns/DIV)
Figure 18. Small Signal Transient Response vs. Capacitive Load
Figure 21. Large Signal Transient Response vs. Capacitive Load
Rev. 0 | Page 9 of 16
07714-020
VS = 3.3V
OUTPUT VOLTAGE, VS = 3.3V (V)
OUTPUT VOLTAGE, VS = 5V (V)
0.10
OUTPUT VOLTAGE (V)
1.0
1.5
07714-019
ADA4858-3
0.15 CL = 10pF
1.5 CL = 10pF
CL = 6pF
1.0
CL = 16pF
0.10
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
CL = 4pF 0.05
CL = 14pF 0.5
0
0
-0.05
-0.5
-0.10
07714-022
-1.0
07714-025
VOUT = 200mV p-p -0.15 TIME (5ns/DIV)
-1.5 TIME (5ns/DIV)
Figure 22. Small Signal Transient Response vs. Capacitive Load
2.0 1.6 1.2 0.8
AMPLITUDE (V)
Figure 25. Large Signal Transient Response vs. Capacitive Load
2.0 1.6 1.2 0.8 ERROR 0.5 0.4 0.3 0.2
0.5 0.4 OUTPUT INPUT 0.3 0.2
ERROR (%)
0 -0.4 -0.8 -1.2 -1.6 -2.0 -5 0 5 10 15 20 25 30 35 ERROR
0 -0.1 -0.2 -0.3 -0.4
0 -0.4 -0.8 -1.2 OUTPUT -1.6 INPUT
0 -0.1 -0.2 -0.3 -0.4 0 5 10 15 20 25 30 35
07714-023
TIME (ns)
TIME (ns)
Figure 23. Settling Time (Rise)
5 4 3 2 1 0 -1 -2 -3 TIME (20ns/DIV) VOUT 2.5 2.0 1.5 3.0 2.5 2.0
Figure 26. Settling Time (Fall)
1.5
VIN
VIN
VS = 3.3V
1.0 VOUT 0.5
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1.0 0.5 0 -0.5 -1.0
1.0 0.5 0 -0.5 -1.0 -1.5
0
-0.5
07714-024
INPUT VOLTAGE (V)
07714-027
1.5
-1.5
-2.0 TIME (20ns/DIV)
-1.0
Figure 24. Output Overdrive Recovery
Figure 27. Output Overdrive Recovery, VS = 3.3 V
Rev. 0 | Page 10 of 16
07714-026
-0.5 40
-2.0 -5
-0.5 40
ERROR (%)
0.4
0.1
AMPLITUDE (V)
0.4
0.1
ADA4858-3
1000 900 800 RISE, G = 1 RISE, G = 2
1000 900 800
SLEW RATE (V/s)
VS = 3.3V
SLEW RATE (V/s)
700 FALL, G = 2 600 500 400 300 200 100
07714-028
700 600 500 400 300 200 100
RISE, G = 2 RISE, G = 1 FALL, G = 2 FALL, G = 1
FALL, G = 1
0
0.5
1.0 1.5 OUTPUT VOLTAGE (V p-p)
2.0
2.5
0
0.5
1.0 1.5 OUTPUT VOLTAGE (V p-p)
2.0
2.5
Figure 28. Slew Rate vs. Output Voltage
0 24 22 20 18 AMPLIFIER CURRENT 16 14 12 OUTPUT VOLTAGE 10 8 5.0
Figure 31. Slew Rate vs. Output Voltage
1.5 VPD 1.0 VOUT
OUTPUT VOLTAGE (V)
CURRENT (mA)
CHARGE PUMP CURRENT
6
CHARGE PUMP OUTPUT VOLTAGE (V)
-0.4 -0.8 -1.2 -1.6 -2.0 -2.4 -2.8 -3.2 2.5
5
POWER DOWN VOLTAGE (V)
07714-033 07714-032
0.5
4
0
3
-0.5
2
-1.0
1
3.0
3.5
4.0
4.5
07714-029
-1.5 TIME (400ns/DIV)
0
CHARGE PUMP SUPPLY VOLTAGE (V)
Figure 29. Charge Pump Output Voltage and Current vs. Supply Voltage
20 18
INPUT VOLTAGE NOISE (nV/ Hz)
Figure 32. Enable/Power Down Time
100 90
INPUT CURRENT NOISE (pA/ Hz)
16 14 12 10 8 6 4 2 1k 10k FREQUENCY (Hz) 100k 1M
07714-030
80 70 60 50 40 30 20 10 0 100 1k 10k FREQUENCY (Hz) -IN +IN 100k 1M
0 100
Figure 30. Input Voltage Noise vs. Frequency
Figure 33. Input Current Noise vs. Frequency
Rev. 0 | Page 11 of 16
07714-031
0
0
ADA4858-3
-100 CHARGE PUMP HARMONICS -105 -110 -115 -120 -125 -130 -135 -140 -145 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
07714-201
-100 CHARGE PUMP HARMONICS -105 -110 -115
VS = 3.3V
POWER (dBm)
POWER (dBm)
-120 -125 -130 -135 -140 -145 -150 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
07714-202
-150
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 34. Output Spectrum vs. Frequency
Figure 35. Output Spectrum vs. Frequency
Rev. 0 | Page 12 of 16
ADA4858-3 THEORY OF OPERATION
OVERVIEW
The ADA4858-3 is a current feedback amplifier designed for exceptional performance as a triple amplifier with a variable gain capability. Its specifications make it especially suitable for SD and HD video applications. The ADA4858-3 provides HD video output on a single supply as low as 3.0 V while only consuming 13 mA per amplifier. It also features a power-down pin (PD) that reduces the quiescent current to 2 mA when activated. The ADA4858-3 can be used in applications that require both ac- and dc-coupled inputs and outputs. The output stage on the ADA4858-3 is capable of driving 2 V p-p video signals into two doubly terminated video loads (150 each) on a single 5 V supply. The input range of the ADA4858-3 includes ground, while the output range is limited by the output headroom set by the voltage drop across the two diodes from each rail, which occurs 1.2 V from the positive and negative supply rails.
+VS CPO C2 1 C1
07714-137 07714-138
a
b
1
Figure 36. C1 Charging Cycle
+VS C1 CPO C2 2 b a 2
Figure 37. C1 Discharging Cycle
The ADA4858-3 specifications make it especially suitable for SD and HD video applications. It also allows dc-coupled video signals with its black level set to 0 V and its sync tip at -300 mV for YPbPr video. The charge pump is always on, even when the power-down pin (PD) is enabled and the amplifier is off. However, if a negative current is not used, it is in an idle state. Each amplifier needs -6.3 mA of current, which totals -19 mA for all three amplifiers. This means additional negative current may be available by the charge pump for external use. Pin 4 (CPO) is the charge pump output, which provides access to the negative supply generated by the charge pump. Placing a 1 F charge capacitor at the CPO pin is essential to hold the charge. If the negative supply is used to power another device in the system, it is only possible for the 5 V supply operation. In the 3.3 V supply operation, the charge pump output current is very limited. The capacitor at the CPO pin, which regulates the ripple of the negative voltage, can be used as a coupling capacitor for the external device. However, the charge pump current should be limited to a maximum of 50 mA for external use. When powering down the ADA4858-3, the charge pump is not affected and its output voltage and current is still available for external use.
CHARGE PUMP OPERATION
The on-board charge pump creates a negative supply for the amplifier. It provides different negative voltages depending on the power supply voltage. For a +5 V supply, the negative supply generated is equal to -3 V with 150 mA of output supply current, and for a +3.3 V supply, the negative supply is equal to -2 V with 45 mA of output supply current. Figure 36 shows the charging cycle when the supply voltage +VS charges C1 through 1 to ground. During this cycle, C1 quickly charges to reach the +VS voltage. The discharge cycle then begins with switching 1 off and switching 2 on, as shown in Figure 37. When C1 = C2, the charge in C1 is divided between the two capacitors and slowly increases the voltage in C2 until it reaches a predetermined voltage (-3 V for +5 V supply and -2 V for +3.3 V supply). The typical charge pump charging and discharging frequency is 550 kHz with a 150 load and no input signal. This frequency changes with the load current, and it can reach the dc level if the amplifier is powered down.
Rev. 0 | Page 13 of 16
ADA4858-3 APPLICATIONS INFORMATION
GAIN CONFIGURATIONS
The ADA4858-3 is a single-supply, high speed, voltage feedback amplifier. Table 5 provides a convenient reference for quickly determining the feedback and gain set resistor values and bandwidth for common gain configurations. Table 5. Recommended Values and Frequency Performance1
Gain 1 2 5
1
The choice of RF and RG should be carefully considered for maximum flatness vs. power dissipation trade-off. In this case, the flatness is over 90 MHz, which is more than the high definition video requirement.
5V C1 10F C2 0.1F
RF () 402 249 200
RG () N/A 249 40
Small Signal -3 dB BW (MHz) 600 450 160
Large Signal 0.1 dB Flatness (MHz) 88 95 35
VIN R1 75
+
U1
ADA4858-3 -
R4 75
VOUT R5 75
Conditions: VS = 5 V, TA = 25C, RL = 150 .
-VS
+VS
10F
Figure 40. DC-Coupled, Single-Supply Schematic
MULTIPLE VIDEO DRIVER
VIN
+
0.1F
ADA4858-3 -
RF
VOUT
In applications requiring that multiple video loads be driven simultaneously, the ADA4858-3 can deliver 5 V supply operation. Figure 41 shows the ADA4858-3 configured with two video loads, and Figure 42 shows the two video load performances.
RF 249
07714-139
RG
+VS
10F
Figure 38. Noninverting Gain Configuration
RF +VS 10F
RG 249
-
0.1F 75 75 CABLE VOUT1 75 75 75 CABLE VOUT2 75
07714-142 07714-040
75 CABLE
VIN RG
ADA4858-3 +
75
-
0.1F
VIN
ADA4858-3 +
VOUT
07714-140
Figure 41. Video Driver Schematic for Two Video Loads
6.5 RL = 150 6.0
Figure 39. Inverting Gain Configuration
DC-COUPLED VIDEO SIGNAL
The ADA4858-3 does not have a rail-to-rail output stage. The output can be within 1 V of the rails. Having a charge pump on-board that can provide -3 V on a +5 V supply and -2 V on +3.3 V supply makes this part excellent for video applications. In dc-coupled applications, the black color has a 0 V voltage reference. This means that the output voltage should be able to reach 0 V, which is feasible with the presence of the charge pump. Figure 40 shows the schematic of a dc-coupled, single-supply application. It is similar to dual-supply application, where the input is properly terminated with a 50 resistor to ground. The amplifier itself is set at a gain of 2 to account for the input termination loss.
CLOSED-LOOP GAIN (dB)
5.5 5.0 4.5 4.0 3.5 3.0 2.5 1 VS = 5V RF = 301 G=2 VOUT = 2V p-p 10
RL = 75
100
07714-141
Figure 38 and Figure 39 show the typical noninverting and inverting configurations and the recommended bypass capacitor values.
R2 249
R3 249
1000
FREQUENCY (MHz)
Figure 42. Large Signal Frequency Response for Various Loads
Rev. 0 | Page 14 of 16
ADA4858-3
PD (POWER-DOWN) PIN
The ADA4858-3 is equipped with a PD (power-down) pin for all three amplifiers. This allows the user the ability to reduce the quiescent supply current when an amplifier is not active. The power-down threshold levels are derived from ground level. The amplifiers are powered down when the voltage applied to the PD pin is greater than a certain voltage from ground. In a 5 V supply application, the voltage is greater than 2 V, and in a 3.3 V supply application, the voltage is greater than 1.5 V. The amplifier is enabled whenever the PD pin is left floating (not connected). If the PD pin is not used, it is best to leave it floating or connected to ground. Note that the power-down feature does not control the charge pump output voltage and current. Table 6. Power-Down Voltage Control
PD Pin Not Active Active 5V <1.5 V >2 V 3.3 V <1 V >1.5 V
LAYOUT
As is the case with all high speed applications, careful attention to printed circuit board (PCB) layout details prevents associated board parasitics from becoming problematic. The ADA4858-3 can operate at up to 600 MHz; therefore, proper RF design techniques must be employed. The PCB should have a ground plane covering all unused portions of the component side of the board to provide a low impedance return path. Removing the ground plane on all layers from the area near and under the input and output pins reduces stray capacitance. Signal lines connecting the feedback and gain resistors should be kept as short as possible to minimize the inductance and stray capacitance associated with these traces. Termination resistors and loads should be located as close as possible to their respective inputs and outputs. Input and output traces should be kept as far apart as possible to minimize coupling (crosstalk) through the board. Adherence to microstrip or stripline design techniques for long signal traces (greater than 1 inch) is recommended. For more information on high speed board layout, see "A Practical Guide to High-Speed Printed-Circuit-Board Layout", Analog Dialogue, Volume 39, Number 3, September 2005 at www.analog.com.
POWER SUPPLY BYPASSING
Careful attention must be paid to bypassing the power supply pins of the ADA4858-3. High quality capacitors with low equivalent series resistance (ESR), such as multilayer ceramic capacitors (MLCCs), should be used to minimize supply voltage ripple and power dissipation. A large, usually tantalum, capacitor between 2.2 F to 47 F located in proximity to the ADA4858-3 is required to provide good decoupling for lower frequency signals. The actual value is determined by the circuit transient and frequency requirements. In addition, 0.1 F MLCC decoupling capacitors should be located as close to each of the power supply pins and across from both supplies as is physically possible, no more than 1/8-inch away. The ground returns should terminate immediately into the ground plane. Locating the bypass capacitor return close to the load return minimizes ground loops and improves performance.
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ADA4858-3 OUTLINE DIMENSIONS
4.00 BSC SQ 0.60 MAX 0.60 MAX 0.65 BSC 3.75 BSC SQ 0.75 0.60 0.50
(BOTTOM VIEW)
PIN 1 INDICATOR
13 12
16
PIN 1 INDICATOR
1
TOP VIEW
2.25 2.10 SQ 1.95
5 4
9
8
0.25 MIN 1.95 BSC
12 MAX 1.00 0.85 0.80
0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM
SEATING PLANE
0.35 0.30 0.25
0.20 REF
COPLANARITY 0.08
FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET.
072808-A
COMPLIANT TO JEDEC STANDARDS MO-220-VGGC
Figure 43.16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm x 4 mm Body, Very Thin Quad (CP-16-4) Dimensions shown in millimeters
ORDERING GUIDE
Model ADA4858-3ACPZ-R2 1 ADA4858-3ACPZ-R71 ADA4858-3ACPZ-RL1
1
Temperature Range -40C to +105C -40C to +105C -40C to +105C
Package Description 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ
Package Option CP-16-4 CP-16-4 CP-16-4
Ordering Quantity 250 1,500 5,000
Z = RoHS Compliant Part.
(c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07714-0-10/08(0)
Rev. 0 | Page 16 of 16

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