AD780 ,2.5 V/3.0 V Ultrahigh Precision Bandgap Voltage ReferenceSPECIFICATIONS (T = 25C, V = 5 V, unless otherwise noted.)A INAD780AN/AR AD780CR AD780BN/BRParamet ..
AD7801BR ,+2.7 V to +5.5 V, Parallel Input, Voltage Output 8-Bit DACSPECIFICATIONSMIN MAX1Parameter B Versions Units Conditions/CommentsSTATIC PERFORMANCEResolution 8 ..
AD7801BRU ,+2.7 V to +5.5 V, Parallel Input, Voltage Output 8-Bit DACapplications.buffer allows the DAC output to swing rail to rail. The AD7801has a parallel microproc ..
AD7801BRZ-REEL , 2.7 V to 5.5 V, Parallel Input, Voltage Output 8-Bit DAC
AD7804BN ,+3.3 V to +5 V Quad/Octal 10-Bit DACsFeatures Channels Controlled Main DAC Sub DACDATA DACCHANNEL BHardware Clear All ÏÏREGISTER REGISTE ..
AD7804BR ,+3.3 V to +5 V Quad/Octal 10-Bit DACsGENERAL DESCRIPTIONCONTROL LOGICSDINThe AD7804/AD7808 are quad/octal 10-bit digital-to-analog**ONLY ..
ADM1818-20ART-RL7 ,Microprocessor Reset CircuitsFEATURES FUNCTIONAL BLOCK DIAGRAMSReliable Low Cost Voltage Monitor with Reset OutputSupports Monit ..
ADM1818-5ART-REEL7 , Microprocessor Reset Circuits
ADM1818-5ART-REEL7 , Microprocessor Reset Circuits
ADM1818-5ART-REEL7 , Microprocessor Reset Circuits
ADM1818-R22ART-RL7 , Microprocessor Reset Circuits
ADM1818-R22ART-RL7 , Microprocessor Reset Circuits
AD780
2.5 V/3.0 V Ultrahigh Precision Bandgap Voltage Reference
REV.C
2.5 V/3.0 V
High Precision Reference
FUNCTIONAL BLOCK DIAGRAM
+VIN
VOUT
TRIM
GNDO/P SELECT
2.5V – NC
3.0V – GND
TEMP
NC = NO CONNECT
PRODUCT DESCRIPTIONThe AD780 is an ultrahigh precision band gap reference voltage
that 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 preci-
sion reference application. A unique low headroom design facili-
tates 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 pro-
vides 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 and SOIC
packages. The AD780AN, AD780AR, AD780BN, AD780BR,
and AD780CR are specified for operation from –40°C to +85°C.
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)
PRODUCT HIGHLIGHTSThe AD780 provides a pin-programmable 2.5 V or 3.0 V
output from a 4 V to 36 V input.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.For applications requiring even higher accuracy, an optional
fine-trim connection is provided.The AD780 noise is extremely low, typically 4 mV 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.The temperature output pin enables the AD780 to be con-
figured as a temperature transducer while providing a stable
output reference.
(TA = 25�C, VIN = 5 V, unless otherwise noted.)LINE REGULATION
LOAD REGULATION, SHUNT MODE
LONG TERM STABILITY
TEMPERATURE PIN
NOTESMaximum output voltage drift is guaranteed for all packages.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.The long term stability specification is noncumulative. The drift in subsequent 1000 hr. periods is significantly lower than in the first 1000 hr. period.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.
Specifications subject to change without notice.
AD780–SPECIFICATIONS
ORDERING GUIDE
ABSOLUTE MAXIMUM RATINGS*+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 perma-
nent 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 specifi-
cation is not implied. Exposure to absolute maximum specifications for extended
periods may affect device reliability.
PIN CONFIGURATION
8-Lead Plastic DIP and SOIC Packages
DIE LAYOUTNOTES
Both VOUT pads should be connected to the output.
Die Thickness: The standard thickness of Analog Devices bipolar dice is24 mil ±2 mil.
Die Dimensions: The dimensions given have a tolerance of ±2 mil.
Backing: The standard backside surface is silicon (not plated). Analog Devicesdoes not recommend gold-backed dice for most applications.
Edges: A diamond saw is used to separate wafers into dice thus providing per-pendicular edges halfway through the die. In contrast to scribed dice, this tech-
nique provides a more uniform die shape and size. The perpendicular edges
facilitate handling (such as tweezer pickup), while the uniform shape and size
simplify substrate design and die attach.
Top Surface: The standard top surface of the die is covered by a layer ofglassivation. All areas are covered except bonding pads and scribe lines.
Surface Metalization: The metalization to Analog Devices bipolar dice isaluminum. Minimum thickness is 10,000 A.
Bonding Pads: All bonding pads have a minimum size of 4.0 mil by 6.0 mil.The passivation windows have a 3.6 mil by 5.6 mil minimum size.
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V 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.
THEORY OF OPERATIONBand gap 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 band gap voltage.
In the AD780, the band gap cell contains two npn transistors
(Q6 and Q7) that differ in emitter area by 12�. The difference in
their Vbes produces a PTAT current in R5. This, in turn,
produces a PTAT voltage across R4 that, when combined with
the Vbe of Q7, produces a voltage Vbg that does not vary with tem-
perature. Precision laser trimming of the resistors and other pat-
ented circuit techniques are used to further enhance the drift
performance.
+VIN
VOUT
TRIM
GNDO/P SELECT
2.5V – NC
3.0V – GND
TEMP
NC = NO CONNECTFigure 1. Schematic Diagram
The output voltage of the AD780 is determined by the configu-
ration 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 ther-
mometer output voltage (at Pin 3) that increases at a rate of ap-
proximately 2 mV/°C.
The AD780’s NC (Pin 7) is a 20 kΩ resistor to V+ that 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.
APPLYING THE AD780The 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
5V. This increases by ~2 µA/V up to 36V.
Figure 2.Optional Fine Trim Circuit
Initial error can be nulled using a single 25 kΩ 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., 1–5 MΩ)
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 kΩ/RNULL for either the 2.5 V or
3.0 V mode.
The external null resistor affects the overall temperature coeffi-
cient by a factor equal to the percentage of VOUT nulled.
For example, a 1 mV (0.03%) 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).
NOISE PERFORMANCEThe 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 compensa-
tion capacitor, C2, between the TEMP pin and ground. Suitable
values are shown in Figure 3.
AD780
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.
Figure 4.Standalone Noise Performance
Figure 5.Noise Reduction Circuit
NOISE COMPARISONThe wideband noise performance of the AD780 can also be
expressed in ppm. The typical performance with C1 and C2 is
0.6ppm and without external capacitors is 1.2 ppm.
This performance is respectively 7� and 3� lower than the
specified performance of the LT1019.
Figure 6.Reduced Noise Performance with C1 = 100 µF,
C2 = 100 nF
TEMPERATURE PERFORMANCEThe 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 non-
linearity 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.
Figure 7.Typical AD780BN Temperature Drift
TEMPERATURE OUTPUT PINThe AD780 provides a TEMP output (Pin 3) that varies
linearly with temperature. This output can be used to monitor
changes in system ambient temperature and to initiate calibration
of the system if desired. The voltage VTEMP is 560 mV at 25°C,
and the temperature coefficient is approximately 2 mV/°C.
Figure 8 shows the typical VTEMP characteristic curve over
temperature taken at the output of the op amp with a noninverting
gain of five.
TEMPERATURE – �C
VOLTAGE – V
OUTFigure 8.Temperature Pin Transfer Characteristic
Since the TEMP voltage is acquired from the band gap core
circuit, current pulled from this pin will have a significant effect
on VOUT. Care must be taken to buffer the TEMP output with a
suitable op amp, e.g., an OP07, AD820, or AD711 (all of which
would result in less than a 100 µV change in VOUT). The relation-
ship between ITEMP and VOUT is as follows:
∆VOUT = 5.8 mV/µA × ITEMP (2.5 V range)
∆VOUT = 6.9 mV/µA × ITEMP (3.0 V range)
Notice how sensitive the current dependent factor on VOUT is.large amount of current, even in tens of microamp, drawn
from the TEMP pin can cause VOUT and TEMP output to fail.
The choice of C1 and C2 was dictated primarily by the need for a
relatively flat response that rolled off early in the high-frequency
noise at the output. But there is considerable margin in the choice
of these capacitors. For example, the user can actually put a huge
C2 on the TEMP pin with none on the output pin. However, one
must either put very little or a lot of capacitance at the TEMP pin.
Intermediate values of capacitance can sometimes cause oscillation.
In any case, the user should follow the recommendation in Figure 3.
TEMPERATURE TRANSDUCER CIRCUITThe circuit shown in Figure 9 is a temperature transducer that
amplifies the TEMP output voltage by a gain of a little over +5
to provide a wider full-scale output range. The trimpot can be
used to adjust the output so it varies exactly by 10 mV/°C.
To minimize resistance changes with temperature, resistors with
low temperature coefficients, such as metal film resistors, should
be used.
Figure 9.Differential Temperature Transducer
SUPPLY CURRENT OVER TEMPERATUREThe AD780’s quiescent current will vary slightly over temperature
and input supply range. The test limit is 1 mA over the indus-
trial and 1.3 mA over the military temperature range. Typical
performance with input voltage and temperature variation is shown
in Figure 10.
Figure 10.Typical Supply Current over Temperature
AD780
