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AD780ANADIN/a2043avai2.5 V/3.0 V High Precision Reference
AD780ARN/a1avai2.5 V/3.0 V High Precision Reference
AD780BNTIN/a1000avai2.5 V/3.0 V High Precision Reference
AD780BRADIN/a500avai2.5 V/3.0 V High Precision Reference
AD780BR-REEL7 |AD780BRREEL7ADN/a256avai2.5 V/3.0 V High Precision Reference
AD780CRADN/a710avai2.5 V/3.0 V High Precision Reference


AD780AN ,2.5 V/3.0 V High Precision ReferenceSpecifications subject to change without notice.–2– REV. BAD780ABSOLUTE MAXIMUM RATINGS* DIE LAYOUT ..
AD780AR ,2.5 V/3.0 V High Precision ReferenceSPECIFICATIONSAD780AN/AR AD780CR AD780BN/BRParameter Min Typ Max Min Typ Max Min Typ Max UnitOUTPUT ..
AD780ARZ-REEL7 , 2.5 V/3.0 V High Precision Reference
AD780ARZ-REEL7 , 2.5 V/3.0 V High Precision Reference
AD780BN ,2.5 V/3.0 V High Precision ReferenceFEATURES FUNCTIONAL BLOCK DIAGRAMPin-Programmable 2.5 V or 3.0 V Output+VINUltralow Drift: 3 ppm/C ..
AD780BR ,2.5 V/3.0 V High Precision Referencespecifications for extendedperiods may affect device reliability.PIN CONFIGURATION8-Lead Plastic DI ..
ADM202EARNZ-REEL , EMI/EMC-Compliant, -15 kV, ESD-Protected RS-232 Line Drivers/Receivers
ADM202EARNZ-REEL , EMI/EMC-Compliant, -15 kV, ESD-Protected RS-232 Line Drivers/Receivers
ADM202EARU ,EMI/EMC Compliant, +-15 kV ESD Protected, RS-232 Line Drivers/ReceiversCHARACTERISTICSMaximum Data Rate 230 kbps R = 3 kΩ to 7 kΩ, C = 50 pF to 2500 pFL LReceiver Propaga ..
ADM202EARW ,EMI/EMC Compliant, +-15 kV ESD Protected, RS-232 Line Drivers/ReceiversFEATURES FUNCTIONAL BLOCK DIAGRAMSComplies with 89/336/EEC EMC Directive+5V INPUTESD Protection to ..
ADM202EARW-REEL , EMI/EMC-Compliant, -15 kV, ESD-Protected RS-232 Line Drivers/Receivers
ADM202EARWZ , EMI/EMC-Compliant, -15 kV, ESD-Protected RS-232 Line Drivers/Receivers


AD780AN-AD780AR-AD780BN-AD780BR-AD780BR-REEL7-AD780CR
2.5 V/3.0 V High Precision Reference
REV.B2.5 V/3.0 V
High Precision Reference
FUNCTIONAL BLOCK DIAGRAM
TEMP
+VIN
VOUT
TRIM
GNDO/P SELECT
2.5V - NC
3.0V - GND
NC = NO CONNECT8
PRODUCT DESCRIPTION

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 com-
bined 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 nega-
tive 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 condi-
tions 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, al-
lowing 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.
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 HIGHLIGHTS
The 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 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.The temperature output pin enables the AD780 to be config-
ured as a temperature transducer while providing a stable
output reference voltage.
AD780–SPECIFICATIONS
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.
*Same as AD780AN/AR specification.
Specifications subject to change without notice.
(TA = +25�C, VIN = +5 V unless otherwise noted)
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, SOIC and Cerdip Packages
2.5/3.0V SELECT
(NC OR GND)
VOUT
TRIM
+VIN
TEMP
GND
NC = NO CONNECT
DIE LAYOUT

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 per-

pendicular 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 alu-

minum. 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.
CAUTION

ESD (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.
AD780
THEORY OF OPERATION

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 differ-
ence in their Vbe’s produces a PTAT current in R5. This in
turn produces a PTAT voltage across R4, which when com-
bined 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.
Figure 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 regula-
tor providing a –2.5 V or –3.0 V reference voltage output with-
out external components.
The PTAT voltage is also used to provide the user with a ther-
mometer output voltage (at Pin 3) which increases at a rate of
approximately 2 mV/°C.
The AD780’s NC Pin 7 is a 20 kΩ resistor to V+ which is used
solely for production test purposes. Users who are currently us-
ing the LT1019 self-heater pin (Pin 7) must take into account
the different load on the heater supply.
APPLYING THE AD780

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 de-
pending 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.
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 (.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 coeffi-
cients of less than 100 ppm/°C).
NOISE PERFORMANCE
The impressive noise performance of the AD780 can be further
improved if desired by the addition of two capacitors: a load ca-
pacitor C1 between the output and ground, and a compensation
capacitor C2 between the TEMP pin and ground. Suitable val-
ues are shown in Figure 3.
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.
Figure 4.Stand-Alone Noise Performance
Figure 5.Noise Reduction Circuit
NOISE COMPARISON

The wideband noise performance of the AD780 can also be ex-
pressed 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� lower than the
specified performance of the LT1019.
Figure 6. Reduced Noise Performance with C1 = 100 µF,
C2 = 100 nF
TEMPERATURE PERFORMANCE

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 volt-
ages 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
AD780
TEMPERATURE OUTPUT PIN

The 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 tem-
perature taken at the output of the op amp with a noninverting
gain of five.
TEMPERATURE – �C
VOLTAGE
OUT

Figure 8. Temperature Pin Transfer Characteristic
Since the TEMP voltage is acquired from the bandgap core cir-
cuit, 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 rela-
tionship 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. A
large amount of current, even in tens of microamp, drawn from
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 recom-
mendation in Figure 3.
TEMPERATURE TRANSDUCER CIRCUIT

The circuit shown in Figure 9 is a temperature transducer which
a 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 TEMPERATURE

The AD780’s quiescent current will vary slightly over tempera-
ture and input supply range. The test limit is 1 mA over the in-
dustrial and 1.3 mA over the military temperature range.
Typical performance with input voltage and temperature varia-
tion is shown in Figure 10 following.
Figure 10. Typical Supply Current over Temperature
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