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ISL28278, ISL28478
Data Sheet July 11, 2007 FN6145.2
Dual and Quad Micropower Single Supply Rail-to-Rail Input and Output (RRIO) Op-Amp
The ISL28278 and ISL28478 are dual and quad channel micropower operational amplifiers optimized for single supply operation over the 2.4V to 5V range. They can be operated from one lithium cell or two Ni-Cd batteries. For equivalent performance in a single channel op-amp reference EL8178. These devices feature an Input Range Enhancement Circuit (IREC) which enables them to maintain CMRR performance for input voltages 10% above the positive supply rail and to 100mV below the negative supply. The output operation is rail to rail. The ISL28278 and ISL28478 draw minimal supply current while meeting excellent DC-accuracy, AC-performance, noise and output drive specifications. The ISL28278 contains a power down enable pin that reduces the power supply current to typically 4A in the disabled state.
Features
* Low power 120A typical supply current (ISL28278) * 225V max offset voltage * 30pA max input bias current * 300kHz typical gain-bandwidth product * 105dB typical PSRR * 100dB typical CMRR * Single supply operation down to 2.4V * Input is capable of swinging above V+ and below V(ground sensing) * Rail-to-rail input and output (RRIO) * Enable Pin (ISL28278 only) * Pb-free plus anneal available (RoHS compliant)
Applications
* Battery- or solar-powered systems * 4mA to 25mA current loops
Pinouts
ISL28278 (16 LD QSOP) TOP VIEW
NC 1 NC 2 OUT_A 3 + IN-_A 4 IN+_A 5 EN_A 6 V- 7 NC 8 + 16 NC 15 V+ 14 OUT_B 13 IN-_B 12 IN+_B 11 EN_B 10 NC 9 NC
* Handheld consumer products * Medical devices * Thermocouple amplifiers * Photodiode pre-amps * pH probe amplifiers
Ordering Information
PART NUMBER (Note) ISL28278FAZ* ISL28478FAZ* PART MARKING 28278FAZ 28478FAZ PACKAGE (Pb-Free) 16 Ld QSOP 16 Ld QSOP PKG. DWG. # MDP0040 MDP0040
ISL28478 (16 LD QSOP) TOP VIEW
OUT_A 1 IN-_A 2 + IN+_A 3 V+ 4 IN+_B 5 IN-_B 6 OUT_B 7 NC 8 + + + 16 OUT_D 15 IN-_D 14 IN+_D 13 V12 IN+_C 11 IN-_C 10 OUT_C 9 NC
*"-T7" suffix is for tape and reel. Please refer to TB347 for details on reel specifications. NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2006, 2007. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
ISL28278, ISL28478
Absolute Maximum Ratings (TA = +25C)
Supply Voltage, V- to V+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V Supply Turn On Voltage Slew Rate . . . . . . . . . . . . . . . . . . . . . 1V/s Differential Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5mA Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5V Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . V- - 0.5V to V+ + 0.5V ESD Tolerance Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3kV Machine Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300V
Thermal Information
Thermal Resistance JA (C/W) 16 Ld QSOP Package . . . . . . . . . . . . . . . . . . . . . . . 112 Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . .Indefinite Ambient Operating Temperature Range . . . . . . . . .-40C to +125C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65C to +150C Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . +125C Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and result in failures not covered by warranty. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Operating Junction
Electrical Specifications
V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, TA = +25C unless otherwise specified. Boldface limits apply over the operating temperature range, -40C to +125C, temperature data established by characterization CONDITIONS MIN (Note 1) TYP MAX (Note 1) UNIT
PARAMETER DC SPECIFICATIONS VOS V OS --------------T IOS IB CMIR CMRR PSRR AVOL
DESCRIPTION
Input Offset Voltage Input Offset Voltage vs Temperature Input Offset Current -40C to +85C Input Bias Current -40C to +85C Common-Mode Voltage Range Common-Mode Rejection Ratio Power Supply Rejection Ratio Large Signal Voltage Gain Guaranteed by CMRR VCM = 0V to 5V V+ = 2.4V to 5V VO = 0.5V to 4.5V, RL = 100k VO = 0.5V to 4.5V, RL = 1k
-225 -450
0.20
225 450
V V/C
1.0 -30 -80 -30 -80 0 80 75 85 80 200 190 100 105 300 60 3 130 4.990 4.97 4.800 4.750 4.996 4.880 120 240 4 156 175 315 350 7 9 6 30 175 225
5
30 80 30 80 5
pA pA V dB dB V/mV V/mV mV mV V V A A A
10
VOUT
Maximum Output Voltage Swing
Output low, RL = 100k Output low, RL = 1k Output high, RL = 100k Output high, RL = 1k
IS,ON
Quiescent Supply Current, Enabled
ISL28278, All channels enabled. ISL28478, All channels enabled.
IS,OFF
Quiescent Supply Current, Disabled
All channels disabled. ISL28278
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FN6145.2 July 11, 2007
ISL28278, ISL28478
Electrical Specifications
V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, TA = +25C unless otherwise specified. Boldface limits apply over the operating temperature range, -40C to +125C, temperature data established by characterization (Continued) CONDITIONS RL = 10 RL = 10 V- to V+ ISL28278 ISL28278 VEN = V+ ISL28278 VEN = VISL28278 0.8 0 MIN (Note 1) 29 24 24 20 2.4 2 0.8 1 1.5 0.1 TYP 31 26 5.0 MAX (Note 1) UNIT mA mA V V V A A
PARAMETER IO+ IOVSUPPLY VENH VENL IENH IENL
DESCRIPTION Short Circuit Sourcing Capability Short Circuit Sinking Capability Supply Operating Range EN Pin High Level EN Pin Low Level EN Pin Input High Current EN Pin Input Low Current
AC SPECIFICATIONS GBW en Gain Bandwidth Product Input Noise Voltage Peak-to-Peak Input Noise Voltage Density in CMRR @ 60Hz PSRR+ @ 120Hz PSRR- @ 120Hz Input Noise Current Density Input Common Mode Rejection Ratio Power Supply Rejection Ratio, +V Power Supply Rejection Ratio, -V AV = 100, RF = 100k, RG = 1k, RL = 10k to VCM f = 0.1Hz to 10Hz fO = 1kHz fO = 1kHz VCM = 1VP-P, RL = 10k to VCM
V+,V- = 1.2V and 2.5V, VSOURCE = 1VP-P, RL = 10k to VCM V+,V- = 1.2V and 2.5V VSOURCE = 1VP-P, RL = 10k to VCM
300 4.5 45 0.04 -70 -80 -60
kHz VP-P nV/Hz pA/Hz dB dB dB
TRANSIENT RESPONSE SR tEN Slew Rate Enable to Output Turn-on Delay Time, 10% EN to 10% Vout Enable to Output Turn-off Delay Time, 10% EN to 10% Vout NOTE: 1. Parts are 100% tested at +25C. Over temperature limits established by characterization and are not production tested. VEN = 5V to 0V, AV = -1, RG = RF = RL = 1k to VCM, ISL28278 VEN = 0V to 5V, AV = -1, RG = RF = RL = 1k to VCM, ISL28278
0.12 0.09 0.14 0.16 0.21
V/s s s
2 0.1
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
+1 0 -1 -2 GAIN (dB) -3 -4 -5 -6 -7 8 1k VOUT = 50mVP-P AV = 1 CL = 3pF RF = 0, RG = INF 10k 100k FREQUENCY (Hz) 1M 5M V+,V-= 2.5V RL = 10k V+,V-= 2.5V RL = 1k V+,V-= 1.2V RL = 1k GAIN (dB) V+,V-= 1.2V RL = 10k 45 40 35 30 25 20 15 10 5 0 100 AV = 100 RL = 10k CL = 3pF RF = 100k RG = 1k 1k V+,V-= 2.5V V+,V-= 1.2V
V+,V-= 1.0V
10k FREQUENCY (Hz)
100k
1M
FIGURE 1. FREQUENCY RESPONSE vs SUPPLY VOLTAGE
FIGURE 2. FREQUENCY RESPONSE vs SUPPLY VOLTAGE
120 80 GAIN GAIN (dB) 40 0 PHASE -40 -80 1 10 100 1k 10k 100k 1M FREQUENCY (Hz)
80 40 PHASE () GAIN (dB) 0 -40 -80 -120 10M
100 80 PHASE 60 40
200 150 100 50 0 PHASE ()
20 0 -20 10
GAIN
-50 -100 -150 1M
100
1k
10k
100k
FREQUENCY (Hz)
FIGURE 3. AVOL vs FREQUENCY @ 100k LOAD
FIGURE 4. AVOL vs FREQUENCY @ 1k LOAD
10 0 -10 -20 PSRR (dB) -30 -40 -50 -60 -70 -80 -90
10
V+,V- = 2.5VDC
VSOURCE = 1VP-P RL = 10k AV = +1 PSRR CMRR (dB)
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 10
V+,V- = 2.5VDC VSOURCE = 1VP-P RL = 10k
PSRR +
-100 10
100
1k
10k
100k
1M
100
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FIGURE 5. PSRR vs FREQUENCY
FIGURE 6. CMRR vs FREQUENCY
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
1k VOLTAGE NOISE (nV/Hz) CURRENT NOISE (fA/Hz) 1 10 100 FREQUENCY (Hz) 1k 10k 1k
100
100
10
10 1 10 100 FREQUENCY (Hz) 1k 10k
FIGURE 7. VOLTAGE NOISE vs FREQUENCY
FIGURE 8. CURRENT NOISE vs FREQUENCY
2.56 2.5 VOLTAGE NOISE (0.5V/DIV) 2.0 1.5 VOLTS (V) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 2.42 0 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 TIME (1s/DIV) TIME (s) 2.46 2.44 2.52 VOUT 2.50 2.48 V+ = 5VDC VOUT = 0.1VP-P RL = 1k AV = +1 VIN 2.54
FIGURE 9. 0.1Hz TO 10Hz INPUT VOLTAGE NOISE
FIGURE 10. SMALL SIGNAL TRANSIENT RESPONSE
5 4 3 2 1 0 0 50 100 150 200 250 VIN 0.1V/DIV V+ = 5VDC VOUT = 4VP-P RL = 1k AV = -2 VOUT 1V/DIV EN INPUT
AV = -1 VIN = 200mVP-P V+ = 5V
VOLTS (V)
0 VOUT
0 10s/DIV TIME (s)
FIGURE 11. LARGE SIGNAL TRANSIENT RESPONSE
FIGURE 12. ISL28278 ENABLE TO OUTPUT DELAY TIME
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
1000 800 600 400 VOS (V) 200 0 -200 -400 -600 -800 -1000 -1 0 1 V+ = 5V RL = OPEN RF = 100k, RG = 100 AV = +1000 2 3 VCM (V) 4 5 6 IBIAS (pA) 100 80 60 40 20 0 -20 -40 -60 -80 -100 -1 0 1 2 3 VCM (V) 4 5 6 V+ = 5V RL = OPEN RF= 100k, RG = 100 AV = +1000
FIGURE 13. INPUT OFFSET VOLTAGE vs COMMON MODE INPUT VOLTAGE
FIGURE 14. INPUT BIAS CURRENT vs COMMON-MODE INPUT VOLTAGE
280 270 260 CURRENT (A) 250 240 230 220 210 200 190 -40
4.8 N = 1000 4.6 MAX 4.4 CURRENT (A) MEDIAN 4.2 4.0 3.8 3.6 MIN 3.4 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 3.2 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 MEDIAN MAX n = 12
MIN
FIGURE 15. ISL28478 SUPPLY CURRENT vs TEMPERATURE, V+,V- = 2.5V, RL = INF
FIGURE 16. ISL28278 DISABLED SUPPLY CURRENT vs TEMPERATURE, V+,V- = 2.5V RL = INF
500 N = 1000 400 300 200 VOS (V) 100 0 -100 -200 -300 -400 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 MIN MAX
500 400 300 200 VOS (V) MEDIAN 100 0 -100 -200 -300 -400 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 MIN MEDIAN N = 1000 MAX
FIGURE 17. VOS vs TEMPERATURE, VIN = 0V, V+,V- = 2.5V
FIGURE 18. VOS vs TEMPERATURE, VIN = 0V, V+,V- = 1.2V
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
500 n = 1000 0 -500 MAX -1000 -1500 MEDIAN -2000 MIN -2500 -40 -20 0 20 40 60 80 100 120 0 -200 IBIAS+ (pA) IBIAS- (pA) -400 -600 -800 -1000 -1200 -1400 -40 -20 0 20 40 60 MEDIAN MAX 200 n = 1000
MIN 80 100 120
TEMPERATURE (C)
TEMPERATURE (C)
FIGURE 19. IBIAS+ vs TEMPERATURE, V+,V- = 2.5V
FIGURE 20. IBIAS- vs TEMPERATURE, V+,V- = 2.5V
500 n = 1000 0 -500 MAX -1000 -1500 -2000 MIN -2500
200 n = 1000 0 -200
IBIAS+ (pA)
IBIAS- (pA)
-400 -600 -800 -1000
MAX
MEDIAN
MEDIAN
MIN -1200 100 120 -40 -20 0 20 40 60 80 100 120
-40
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
FIGURE 21. IBIAS+ vs TEMPERATURE, V+,V- = 1.2V
FIGURE 22. IBIAS- vs TEMPERATURE, V+,V- = 1.2V
200 n = 1000 0 -200 IOS (pA) -400 -600 -800 -1000 -1200 -1400 -40 -20 0 20 40 60 MEDIAN AVOL (V/mV) MAX
550 N = 1000 500 450 400 350 300 250 MIN MIN 80 100 120 200 150 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 MEDIAN MAX
TEMPERATURE (C)
FIGURE 23. IOS vs TEMPERATURE, V+,V- = 2.5V
FIGURE 24. AVOL vs TEMPERATURE, V+,V- = 2.5V, RL = 100k
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
90 N = 1000 80 MAX AVOL (V/mV) CMRR (dB) 70 60 50 40 30 -40 MIN MEDIAN 115 105 95 85 75 -40 MIN 125 135 N = 1000 MAX
MEDIAN
-20
0
20 40 60 80 TEMPERATURE (C)
100
120
-20
0
20 40 60 80 TEMPERATURE (C)
100
120
FIGURE 25. AVOL vs TEMPERATURE, V+,V- = 2.5V, RL = 1k
FIGURE 26. CMRR vs TEMPERATURE, VCM = +2.5V TO -2.5V V+,V- = 2.5V
140 N = 1000 130 120 VOUT (V) 110 100 90 80 -40 MIN MAX
4.91 N = 1000 4.90 MAX 4.89 4.88 4.87 MIN 4.86 4.85 -40 MEDIAN
PSRR (dB)
MEDIAN
-20
0
20 40 60 80 TEMPERATURE (C)
100
120
-20
0
20 40 60 80 TEMPERATURE (C)
100
120
FIGURE 27. PSRR vs TEMPERATURE, V+,V- = 1.2V TO 2.5V
FIGURE 28. VOUT HIGH vs TEMPERATURE, V+,V- = 2.5V, RL= 1k
4.9984 4.9982 4.9980 4.9978 VOUT (V) VOUT (mV) 4.9976 4.9974 4.9972 4.9970 4.9968 4.9966 4.9964 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 MIN MEDIAN n = 12 MAX
160 N = 1000 150 140 MAX 130 MEDIAN 120 MIN 110 100 90 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120
FIGURE 29. VOUT HIGH vs TEMPERATURE, V+,V- = 2.5V, RL= 100k
FIGURE 30. VOUT LOW vs TEMPERATURE, V+,V- = 2.5V, RL= 1k
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Typical Performance Curves V+ = 5V, V- = 0V, VCM = 2.5V, RL = Open, unless otherwise specified.
n = 12 + OUTPUT SHORT CIRCUIT CURRENT (mA) 4.3 4.2 4.1 VOUT (mV) 4.0 3.9 3.8 3.7 3.6 3.5 3.4 -40 -20 0 20 40 60 80 100 120 MIN MEDIAN MAX 41 N = 1000 39 MAX 37 35 33 MEDIAN 31 29 27 25 -40 -20 0 20 40 60 80 100 120 MIN
TEMPERATURE (C)
TEMPERATURE (C)
FIGURE 31. VOUT LOW vs TEMPERATURE, V+,V- = 2.5V, RL= 100k
FIGURE 32. + OUTPUT SHORT CIRCUIT CURRENT vs TEMPERATURE, VIN = -2.55V, RL = 10, V+,V- = 2.5V
- OUTPUT SHORT CIRCUIT CURRENT (mA)
-21 N = 1000 -23 + SLEW RATE (V/s) -25 -27 MEDIAN -29 -31 -33 -40 MIN
0.19 0.18 0.17 0.16 0.15 0.14 0.13 0.12 0.11 0.10 -20 0 20 40 60 80 100 120 0.09 -40 -20 0 20 40 60 80 100 120 MIN MEDIAN MAX N = 1000
MAX
TEMPERATURE (C)
TEMPERATURE (C)
FIGURE 33. - OUTPUT SHORT CIRCUIT CURRENT vs TEMPERATURE, VIN = +2.55V, RL = 10, V+,V- = 2.5V
FIGURE 34. + SLEW RATE vs TEMPERATURE, VOUT = 1.5V, AV = +2
0.20 0.19 0.18 - SLEW RATE (V/s) 0.17 0.16 0.15 0.14 0.13 0.12 0.11 0.10 -40 -20 0 20 40 60 80 100 120 MIN MEDIAN MAX N = 1000
TEMPERATURE (C)
FIGURE 35. - SLEW RATE vs TEMPERATURE, VOUT = 1.5V, AV = +2
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Pin Descriptions
ISL28278 (16 LD QSOP) 3 4 5 15 12 13 14 1, 2, 8, 9, 10, 16 ISL28478 (16 LD QSOP) 1 2 3 4 5 6 7 8, 9 10 11 12 7 13 14 15 16 6 11 PIN NAME OUT_A IN-_A IN+_A V+ IN+_B IN-_B OUT_B NC OUT_C IN-_C IN+_C VIN+_D IN-_D OUT_D EN_A EN_B Circuit 3 Circuit 1 Circuit 1 Circuit 4 Circuit 1 Circuit 1 Circuit 3 Circuit 2 Circuit 2 EQUIVALENT CIRCUIT Circuit 3 Circuit 1 Circuit 1 Circuit 4 Circuit 1 Circuit 1 Circuit 3 Amplifier A output Amplifier A inverting input Amplifier A non-inverting input Positive power supply Amplifier B non-inverting input Amplifier B inverting input Amplifier B output No internal connection Amplifier C output Amplifier C inverting input Amplifier B non-inverting input Negative power supply Amplifier D non-inverting input Amplifier D inverting input Amplifier D output Amplifier A enable pin internal pull-down; Logic "1" selects the disabled state; Logic "0" selects the enabled state. Amplifier B enable pin with internal pull-down; Logic "1" selects the disabled state; Logic "0" selects the enabled state.
V+ LOGIC PIN VCIRCUIT 2 CIRCUIT 3 V+
CAPACITIVELY COUPLED ESD CLAMP
DESCRIPTION
V+ ININ+ V-
V+ OUT V-
VCIRCUIT 4
CIRCUIT 1
Applications Information
Introduction
The ISL28278 and ISL28478 are dual and quad CMOS rail-to-rail input, output (RRIO) micropower operational amplifiers. These devices are designed to operate from a single supply (2.4V to 5.0V) or dual supplies (1.2V to 2.5V) while drawing only 120A (ISL28278) of supply current. This combination of low power and precision performance makes these devices suitable for solar and battery power applications.
undesired change in magnitude and polarity of input offset current. The ISL28278 achieves input rail-to-rail without sacrificing important precision specifications and degrading distortion performance. The devices' input offset voltage exhibits a smooth behavior throughout the entire common-mode input range. The input bias current versus the common-mode voltage range gives us an undistorted behavior from typically 100mV below the negative rail and 10% higher than the V+ rail (0.5V higher than V+ when V+ equals 5V).
Rail-to-Rail Input
Many rail-to-rail input stages use two differential input pairs, a long-tail PNP (or PFET) and an NPN (or NFET). Severe penalties have to be paid for this circuit topology. As the input signal moves from one supply rail to another, the operational amplifier switches from one input pair to the other causing drastic changes in input offset voltage and an
Input Protection
All input terminals have internal ESD protection diodes to the positive and negative supply rails, limiting the input voltage to within one diode beyond the supply rails. There is an additional pair of back-to-back diodes across the input terminals. For applications where the input differential voltage is expected to exceed 0.5V, external series resistors must be used to ensure the input currents never exceed 5mA.
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FN6145.2 July 11, 2007
ISL28278, ISL28478
Rail-to-Rail Output
A pair of complementary MOSFET devices are used to achieve the rail-to-rail output swing. The NMOS sinks current to swing the output in the negative direction. The PMOS sources current to swing the output in the positive direction. Both parts, with a 100k load, will typically swing to within 4mV of the positive supply rail and within 3mV of the negative supply rail. form a continuous loop around both inputs. For further reduction of leakage currents, components can be mounted to the PC board using Teflon standoff insulators.
HIGH IMPEDANCE INPUT IN V+
Enable/Disable Feature
The ISL28278 offers two EN pins (EN_A and EN_B) which disable the op amp when pulled up to at least 2.0V. In the disabled state (output in a high impedance state), the part consumes typically 4A. By disabling the part, multiple parts can be connected together as a MUX. The outputs are tied together in parallel and a channel can be selected by the EN pins. The loading effects of the feedback resistors of the disabled amplifier must be considered when multiple amplifier outputs are connected together. The EN pin also has an internal pull-down. If left open, the EN pin will pull to the negative rail and the device will be enabled by default.
FIGURE 37. GUARD RING EXAMPLE FOR UNITY GAIN AMPLIFIER
Example Application
Thermocouples are the most popular temperature-sensing device because of their low cost, interchangeability, and ability to measure a wide range of temperatures. The ISL28X78 (Figure 38) is used to convert the differential thermocouple voltage into single-ended signal with 10X gain. The ISL28X78's rail-to-rail input characteristic allows the thermocouple to be biased at ground and the amplifier to run from a single 5V supply.
.
Using Only One Channel
The ISL28278 and ISL28478 are dual and quad channel op amps. If the application only requires one channel when using the ISL28278 or less than 4 channels when using the ISL28478, the user must configure the unused channel(s) to prevent them from oscillating. The unused channel(s) will oscillate if the input and output pins are floating. This will result in higher than expected supply currents and possible noise injection into the channel being used. The proper way to prevent this oscillation is to short the output to the negative input and ground the positive input (as shown in Figure 36).
-
R4 100k R3 R2 K TYPE THERMOCOUPLE 10k 10k V+ + ISL28X78 V-
410V/C + 5V
R1 100k
FIGURE 38. THERMOCOUPLE AMPLIFIER
+ 1/2 ISL28278 1/4 ISL28478
Current Limiting
The ISL28278 and ISL28478 have no internal currentlimiting circuitry. If the output is shorted, it is possible to exceed the Absolute Maximum Rating for output current or power dissipation, potentially resulting in the destruction of the device.
FIGURE 36. PREVENTING OSCILLATIONS IN UNUSED CHANNELS
Proper Layout Maximizes Performance
To achieve the maximum performance of the high input impedance and low offset voltage of the ISL28278 and ISL28478, care should be taken in the circuit board layout. The PC board surface must remain clean and free of moisture to avoid leakage currents between adjacent traces. Surface coating of the circuit board will reduce surface moisture and provide a humidity barrier, reducing parasitic resistance on the board. When input leakage current is a concern, the use of guard rings around the amplifier inputs will further reduce leakage currents. Figure 37 shows a guard ring example for a unity gain amplifier that uses the low impedance amplifier output at the same voltage as the high impedance input to eliminate surface leakage. The guard ring does not need to be a specific width, but it should
Power Dissipation
It is possible to exceed the +150C maximum junction temperatures under certain load and power-supply conditions. It is therefore important to calculate the maximum junction temperature (TJMAX) for all applications to determine if power supply voltages, load conditions, or package type need to be modified to remain in the safe operating area. These parameters are related in Equation 1:
T JMAX = T MAX + ( JA xPD MAXTOTAL ) (EQ. 1)
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FN6145.2 July 11, 2007
ISL28278, ISL28478
where: * PDMAXTOTAL is the sum of the maximum power dissipation of each amplifier in the package (PDMAX) * PDMAX for each amplifier is calculated in Equation 2:
V OUTMAX PD MAX = 2*V S x I SMAX + ( V S - V OUTMAX ) x --------------------------RL (EQ. 2)
where: * TMAX = Maximum ambient temperature * JA = Thermal resistance of the package * PDMAX = Maximum power dissipation of 1 amplifier * VS = Supply voltage (Magnitude of V+ and V-) * IMAX = Maximum supply current of 1 amplifier * VOUTMAX = Maximum output voltage swing of the application * RL = Load resistance
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FN6145.2 July 11, 2007
ISL28278, ISL28478 Quarter Size Outline Plastic Packages Family (QSOP)
A D N (N/2)+1
MDP0040
QUARTER SIZE OUTLINE PLASTIC PACKAGES FAMILY INCHES SYMBOL QSOP16 QSOP24 QSOP28 TOLERANCE NOTES
PIN #1 I.D. MARK
A A1 A2 b
0.068 0.006 0.056 0.010 0.008 0.193 0.236 0.154 0.025 0.025 0.041 16
0.068 0.006 0.056 0.010 0.008 0.341 0.236 0.154 0.025 0.025 0.041 24
0.068 0.006 0.056 0.010 0.008 0.390 0.236 0.154 0.025 0.025 0.041 28
Max. 0.002 0.004 0.002 0.001 0.004 0.008 0.004 Basic 0.009 Basic Reference
1, 3 2, 3 Rev. F 2/07
E
E1
1 B 0.010 CAB
(N/2)
c D E
e C SEATING PLANE 0.004 C 0.007 CAB b
H
E1 e L L1 N
L1 A c SEE DETAIL "X"
NOTES: 1. Plastic or metal protrusions of 0.006" maximum per side are not included. 2. Plastic interlead protrusions of 0.010" maximum per side are not included. 3. Dimensions "D" and "E1" are measured at Datum Plane "H". 4. Dimensioning and tolerancing per ASME Y14.5M-1994.
0.010 A2 GAUGE PLANE L 44 DETAIL X
A1
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com 13
FN6145.2 July 11, 2007

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