|
Details, datasheet, quote on part number:AD780AR-REEL7
| |
Datasheet text preview:
a
FEATURES Pin-Programmable 2.5 V or 3.0 V Output Ultralow Drift: 3 ppm/ C max High Accuracy: 2.5 V or 3.0 V 1 mV max Low Noise: 100 nV/Hz Noise Reduction Capability Low Quiescent Current: 1 mA max Output Trim Capability Plug-In Upgrade for Present References Temperature Output Pin Series or Shunt Mode Operation ( 2.5 V, 3.0 V)
2.5 V/3.0 V High Precision Reference AD780
FUNCTIONAL BLOCK DIAGRAM
+VIN 2 NC 7
AD780
R10 R11
NC 1
6
VOUT
R13 Q6
Q7 5 R5 R16 R14 R4 R15 TRIM
PRODUCT DESCRIPTION
TEMP
3
The AD780 is an ultrahigh precision bandgap reference voltage which provides a 2.5 V or 3.0 V output from inputs between 4.0 V and 36 V. Low initial error and temperature drift combined with low output noise and the ability to drive any value of capacitance make the AD780 the ideal choice for enhancing the performance of high resolution ADCs and DACs and for any general purpose precision reference application. A unique low headroom design facilitates a 3.0 V output from a 5.0 V ± 10% input, providing a 20% boost to the dynamic range of an ADC, over performance with existing 2.5 V references. The AD780 can be used to source or sink up to 10 mA and can be used in series or shunt mode, thus allowing positive or negative output voltages without external components. This makes it suitable for virtually any high performance reference application. Unlike some competing references, the AD780 has no "region of possible instability." The part is stable under all load conditions when a 1 µF bypass capacitor is used on the supply. A temperature output pin is provided on the AD780. This provides an output voltage that varies linearly with temperature, allowing the AD780 to be configured as a temperature transducer while providing a stable 2.5 V or 3.0 V output. The AD780 is a pin-compatible performance upgrade for the LT1019(A)2.5 and the AD680. The latter is targeted toward low power applications. The AD780 is available in three grades in plastic DIP, SOIC, and cerdip packages. The AD780AN, AD780AR, AD780BN, AD780BR, and AD780CR are specified for operation from 40°C to +85°C.
4 GND NC = NO CONNECT
8 O/P SELECT 2.5V - NC 3.0V - GND
PRODUCT HIGHLIGHTS
1. The AD780 provides a pin-programmable 2.5 V or 3.0 V output from a 4 V to 36 V input. 2. Laser trimming of both initial accuracy and temperature coefficients results in low errors over temperature without the use of external components. The AD780BN has a maximum variation of 0.9 mV from 40°C to +85°C. 3. For applications requiring even higher accuracy, an optional fine-trim connection is provided. 4. The AD780 noise is extremely low, typically 4 µV p-p from 0.1 Hz to 10 Hz and a wideband spectral noise density of typically 100 nV/Hz. This can be further reduced if desired, by simply using two external capacitors. 5. The temperature output pin enables the AD780 to be configured as a temperature transducer while providing a stable output reference voltage.
REV. B
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2000
AD780SPECIFICATIONS (T = +25 C, V
A
IN
= +5 V unless otherwise noted)
AD780CR Min 2.4985 2.9950 Typ Max 2.5015 3.0050 7 20 AD780BN/BR Min 2.499 2.999 Typ Max 2.501 3.001 3 Unit Volts Volts ppm/ °C ppm/ °C
AD780AN/AR Parameter OUTPUT VOLTAGE 2.5 V Out 3.0 V Out OUTPUT VOLTAGE DRIFT1 40°C to +85°C 55°C to +125°C LINE REGULATION 2.5 V Output, 4 V +VIN 36 V TMIN to TMAX 3.0 V Output, 4.5 V +VIN 36 V TMIN to TMAX LOAD REGULATION, SERIES MODE Sourcing 0 < IOUT < 10 mA TMIN to TMAX Sinking 10 < IOUT < 0 mA 40°C to +85°C 55°C to +125°C LOAD REGULATION, SHUNT MODE I < ISHUNT < 10 mA QUIESCENT CURRENT, 2.5 V SERIES MODE 40°C to +85°C 55°C to +125°C MINIMUM SHUNT CURRENT OUTPUT NOISE 0.1 Hz to 10 Hz Spectral Density, 100 Hz LONG TERM STABILITY3 TRIM RANGE TEMPERATURE PIN Voltage Output @ 25°C Temperature Sensitivity Output Resistance SHORT CIRCUIT CURRENT TO GROUND TEMPERATURE RANGE Specified Performance (A, B, C) Operating Performance (A, B, C)4 Specified Performance (S) Operating Performance (S) 40 55 55 55 4.0 500 560 1.9 3 30 +85 +125 +125 +125 * * * * 620
2
Min 2.495 2.995
Typ
Max 2.505 3.005 7 20
10 10 50 75 75 75 150 75 0.75 0.8 0.7 4 100 20 * * * * * * 1.0 1.3 1.0 * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * *
µV/V µV/V µV/mA µV/mA µV/mA µV/mA µV/mA µV/mA mA mA mA µV p-p nV/ Hz ± ppm/ 1000 Hr ±%
*
mV mV/°C k mA
* * * *
°C °C °C °C
NOTES 1 Maximum output voltage drift is guaranteed for all packages. 2 3.0 V mode typically adds 100 µA to the quiescent current. Also, Iq increases by 2 µA/V above an input voltage of 5 V. 3 The long term stability specification is noncumulative. The drift in subsequent 1000 hr. periods is significantly lower than in the first 1000 hr. period. 4 The operating temperature range is defined as the temperature extremes at which the device will still function. Parts may deviate from their specified performance outside their specified temperature range. *Same as AD780AN/AR specification. Specifications subject to change without notice.
2
REV. B
AD780
ABSOLUTE MAXIMUM RATINGS* DIE LAYOUT
VIN to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V Trim Pin to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V Temp Pin to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V Power Dissipation (25°C) . . . . . . . . . . . . . . . . . . . . . . 500 mW Storage Temperature . . . . . . . . . . . . . . . . . . . 65°C to +150°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . 300°C Output Protection: Output safe for indefinite short to ground and momentary short to VIN. ESD Classification . . . . . . . . . . . . . . . . . . . . . Class 1 (1000 V)
*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 conditions above those indicated in the operational specification is not implied. Exposure to absolute maximum specifications for extended periods may affect device reliability.
PIN CONFIGURATION 8-Lead Plastic DIP, SOIC and Cerdip Packages
NOTES Both VOUT pads should be connected to the output Die Thickness: The standard thickness of Analog Devices Bipolar dice is 24 mils ± 2 mils. Die Dimensions: The dimensions given have a tolerance of ± 2 mils. Backing: The standard backside surface is silicon (not plated). Analog Devices does not recommend gold-backed dice for most applications. Edges: A diamond saw is used to separate wafers into dice thus providing perpendicular edges half-way through the die. In contrast to scribed dice, this technique provides a more uniform die shape and size. The perpendicular edges facilitate handling (such as tweezer pick-up) while the uniform shape and size simplifies substrate design and die attach. Top Surface: The standard top surface of the die is covered by a layer of glassivation. All areas are covered except bonding pads and scribe lines. Surface Metalization: The metalization to Analog Devices bipolar dice is aluminum. Minimum thickness is 10,000Å. Bonding Pads: All bonding pads have a minimum size of 4.0 mils by 6.0 mils. The passivation windows have a 3.6 mils by 5.6 mils minimum size.
NC +V IN TEMP GND
1 2 3 4 NC = NO CONNECT
8
2.5/3.0V SELECT (NC OR GND) NC VOUT TRIM
AD780
TOP VIEW (Not to Scale)
7 6 5
ORDERING GUIDE Initial Error
5.0 mV 5.0 mV 5.0 mV 1.0 mV 1.0 mV 1.0 mV 1.0 mV 1.5 mV 1.5 mV
Model
AD780AN AD780AR AD780AR-REEL7 AD780BN AD780BR AD780BR-REEL AD780BR-REEL7 AD780CR AD780CR-REEL7
Temperature Range
40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C 40°C to +85°C
Temperature Coefficient
7 ppm/°C 7 ppm/°C 7 ppm/°C 3 ppm/°C 3 ppm/°C 3 ppm/°C 3 ppm/°C 7 ppm/°C 7 ppm/°C
Package Options
Plastic Dip SOIC SOIC Plastic Dip SOIC SOIC SOIC SOIC SOIC
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 the AD780 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.
WARNING!
ESD SENSITIVE DEVICE
REV. B
3
AD780
THEORY OF OPERATION APPLYING THE AD780
Bandgap references are the high performance solution for low supply voltage and low power voltage reference applications. In this technique a voltage with a positive temperature coefficient is combined with the negative coefficient of a transistor's Vbe to produce a constant bandgap voltage. In the AD780, the bandgap cell contains two npn transistors (Q6 and Q7) which differ in emitter area by 12 . The difference in their Vbe's produces a PTAT current in R5. This in turn produces a PTAT voltage across R4, which when combined with the Vbe of Q7, produces a voltage Vbg that does not vary with temperature. Precision laser trimming of the resistors and other patented circuit techniques are used to further enhance the drift performance.
+VIN NC
The AD780 can be used without any external components to achieve specified performance. If power is supplied to Pin 2 and Pin 4 is grounded, Pin 6 provides a 2.5 V or 3.0 V output depending on whether Pin 8 is left unconnected or grounded. A bypass capacitor of 1 µF (VIN to GND) should be used if the load capacitance in the application is expected to be greater than 1 nF. The AD780 in 2.5 V mode typically draws 700 µA of Iq at 5 V. This increases by ~2 µA/V up to 36 V.
+VIN NC 1F
NC VOUT
AD780
TRIM TEMP O/P SELECT 2.5V NC 3.0V GND
RNULL R POT.
AD780
R10 R11
GND
NC
VOUT R13
NC = NO CONNECT
Figure 2. Optional Fine Trim Circuit
Q6
Q7 R5 R16 R14 R4 R15 TRIM
TEMP
GND NC = NO CONNECT
O/P SELECT 2.5V - NC 3.0V - GND
Initial error can be nulled using a single 25 k potentiometer connected between VOUT, Trim and GND. This is a coarse trim with an adjustment range of ± 4% and is only included here for compatibility purposes with other references. A fine trim can be implemented by inserting a large value resistor (e.g. 15 M) in series with the wiper of the potentiometer. See Figure 2 above. The trim range, expressed as a fraction of the output, is simply greater than or equal to 2.1 k/RNULL for either the 2.5 V or 3.0 V mode. The external null resistor affects the overall temperature coefficient by a factor equal to the percentage of VOUT nulled. For example a 1 mV (.03%) shift in the output caused by the trim circuit, with a 100 ppm/°C null resistor will add less than 0.06 ppm/°C to the output drift (0.03% 200 ppm/°C, since the resistors internal to the AD780 also have temperature coefficients of less than 100 ppm/°C).
Figure 1. Schematic Diagram
The output voltage of the AD780 is determined by the configuration of resistors R13, R14 and R15 in the amplifier's feedback loop. This sets the output to either 2.5 V or 3.0 V depending on whether R15 (Pin 8) is grounded or not connected. A unique feature of the AD780 is the low headroom design of the high gain amplifier which produces a precision 3 V output from an input voltage as low as 4.5 V (or 2.5 V from a 4.0 V input). The amplifier design also allows the part to work with VIN = VOUT when current is forced into the output terminal. This allows the AD780 to work as a two terminal shunt regulator providing a 2.5 V or 3.0 V reference voltage output without external components. The PTAT voltage is also used to provide the user with a thermometer output voltage (at Pin 3) which increases at a rate of approximately 2 mV/°C. The AD780's NC Pin 7 is a 20 k resistor to V+ which is used solely for production test purposes. Users who are currently using the LT1019 self-heater pin (Pin 7) must take into account the different load on the heater supply.
4
REV. B
AD780
NOISE PERFORMANCE NOISE COMPARISON
The impressive noise performance of the AD780 can be further improved if desired by the addition of two capacitors: a load capacitor C1 between the output and ground, and a compensation capacitor C2 between the TEMP pin and ground. Suitable values are shown in Figure 3.
100
The wideband noise performance of the AD780 can also be expressed in ppm. The typical performance with C1, C2 is 0.6 ppm and without external capacitors is 1.2 ppm. This performance is respectively 7 and 3 specified performance of the LT1019.
NO AMPLIFIER 20 V 10ms
lower than the
COMPENSATION CAP, C2 nF
100 90
10
10
1
0%
10Hz TO 10kHz
0.1 0.1 1 10 100 LOAD CAPACITOR, C1 F
Figure 6. Reduced Noise Performance with C1 = 100 µF, C2 = 100 nF
TEMPERATURE PERFORMANCE
Figure 3. Compensation and Load Capacitor Combinations
C1 and C2 also improve the settling performance of the AD780 when subjected to load transients. The improvement in noise performance is shown in Figures 4, 5 and 6 following.
AMPLIFIER GAIN = 100 100 V
100 90
NO AMPLIFIER 1s
100 90
20 V
10ms
The AD780 provides superior performance over temperature by means of a combination of patented circuit design techniques, precision thin film resistors and drift trimming. Temperature performance is specified in terms of ppm/°C, but because of nonlinearity in the temperature characteristic, the Box-Test method is used to test and specify the part. The nonlinearity takes the form of the characteristic S-shaped curve shown in Figure 7. The Box-Test method forms a rectangular box around this curve, enclosing the maximum and minimum output voltages over the specified temperature range. The specified drift is equal to the slope of the diagonal of this box.
2.0
10 0%
10 0%
0.1 TO 10Hz
10Hz TO 10kHz
1.6 1.2
ERROR mV
Figure 4. Stand-Alone Noise Performance
0.8 0.4
+VIN NC 1F
NC VOUT
0 0.4
AD780
TRIM TEMP C2 O/P SELECT 2.5V NC 3.0V GND C1
0.8 60 40 20 0 20 40 60 80 100 120 140
GND
TEMPERATURE C
Figure 7. Typical AD780BN Temperature Drift
NC = NO CONNECT
Figure 5. Noise Reduction Circuit
REV. B
5
|
|
