ADR435ARM Analog Devices Inc, ADR435ARM Datasheet - Page 15

• Manufacturer Part Number: ADR435ARM
• Description: IC VREF PREC 5V 30MA 8-MSOP
• Manufacturer: Analog Devices Inc
• Series: XFET®r

Specifications of ADR435ARM

• Rohs Status: RoHS non-compliant
• Design Resources: Converting a Single-Ended Signal with AD7982 Differential PulSAR ADC (CN0032) Converting a Single-Ended Signal with AD7984 Differential PulSAR ADC (CN0033) Parametric Measurement Unit and Supporting Components for PAD Appls Using AD5522 and AD7685 (CN0104) Automated Calibration Technique That Reduces AD5360 Offset Voltage to Less Than 1 mV (CN0123) Integrated Device Power Supply for PAD with Output Voltage Range 0 V to 25 V (CN0130) 16 Channels of Programmable Output Span Using AD5360 (CN0131) 40 Channels of Programmable Output Span Using AD5371 (CN0149) Precision Single-Supply Differential ADC Driver for Industrial-Level Signals (CN0180)
• Reference Type: Series
• Voltage - Output: 5V
• Tolerance: ±0.12%
• Temperature Coefficient: 10ppm/°C
• Voltage - Input: 7 ~ 18 V
• Number Of Channels: 1
• Current - Quiescent: 800µA
• Current - Output: 30mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Current - Cathode: -

THEORY OF OPERATION
The ADR43x series of references uses a reference generation
technique known as XFET (eXtra implanted junction FET).
This technique yields a reference with low supply current, good
thermal hysteresis, and exceptionally low noise. The core of the
XFET reference consists of two junction field-effect transistors
(JFETs), one of which has an extra channel implant to raise its
pinch-off voltage. By running the two JFETs at the same drain
current, the difference in pinch-off voltage can be amplified and
used to form a highly stable voltage reference.
The intrinsic reference voltage is around 0.5 V with a negative
temperature coefficient of about −120 ppm/°C. This slope is
essentially constant to the dielectric constant of silicon and can
be compensated closely by adding a correction term generated
in the same fashion as the proportional-to-temperature (PTAT)
term used to compensate band gap references. The primary
advantage of an XFET reference is its correction term, which is
~30 times lower and requires less correction than that of a band
gap reference. Because most of the noise of a band gap reference
comes from the temperature compensation circuitry, the XFET
results in much lower noise.
Figure 29 shows the basic topology of the ADR43x series. The
temperature correction term is provided by a current source
with a value designed to be proportional to absolute temperature.
The general equation is
where:
G is the gain of the reciprocal of the divider ratio.
∆V
I
ADR43x devices are created by on-chip adjustment of R2 and R3 to
achieve 2.048 V or 2.500 V, respectively, at the reference output.
PTAT
P
is the difference in pinch-off voltage between the two JFETs.
V
is the positive temperature coefficient correction current.
I
PTAT
OUT
= G (ΔV
*EXTRA CHANNEL IMPLANT
V
OUT
* *
I
1
= G(ΔV
Figure 29. Simplified Schematic Device
Power Dissipation Considerations
P
– R1 × I
P
I
1
– R1 × I
ΔV
PTAT
P
PTAT
)
)
R1
ADR43x
R3
R2
GND
V
V
IN
OUT
ADR430/ADR431/ADR433/ADR434/ADR435/ADR439
Rev. H | Page 15 of 24
(1)
The ADR43x family of references is guaranteed to deliver load
currents to 10 mA with an input voltage that ranges from 4.1 V
to 18 V. When these devices are used in applications at higher
currents, use the following equation to account for the
temperature effects due to the power dissipation increases:
where:
T
P
θ
BASIC VOLTAGE REFERENCE CONNECTIONS
Voltage references, in general, require a bypass capacitor
connected from V
illustrates the basic configuration for the ADR43x family
of references. Other than a 0.1 µF capacitor at the output to
help improve noise suppression, a large output capacitor at
the output is not required for circuit stability.
NOISE PERFORMANCE
The noise generated by the ADR43x family of references is
typically less than 3.75 µV p-p over the 0.1 Hz to 10.0 Hz band
for ADR430, ADR431, and ADR433. Figure 22 shows the 0.1 Hz
to 10.0 Hz noise of the ADR431, which is only 3.5 µV p-p. The
noise measurement is made with a band-pass filter made of a
2-pole high-pass filter with a corner frequency at 0.1 Hz and a
2-pole low-pass filter with a corner frequency at 10.0 Hz.
HIGH FREQUENCY NOISE
The total noise generated by the ADR43x family of references is
composed of the reference noise and the op amp noise. Figure 31
shows the wideband noise from 10 Hz to 25 kHz. An internal node
of the op amp is brought out on Pin 7, and by overcompensating
the op amp, the overall noise can be reduced.
This is understood by considering that in a closed-loop
configuration, the effective output impedance of an op amp is
where:
R
r
A
β is the feedback factor.
O
JA
D
J
O
VO
and T
is the output resistance of the op amp.
is the device power dissipation.
is the apparent output impedance.
is the device package thermal resistance.
is the open-loop gain at the frequency of interest.
T
V
R
J
IN
O
= P
10µF
A
=
are the junction and ambient temperatures, respectively.
D
1
+
Figure 30. Basic Voltage Reference Configuration
+
× θ
r
A
O
0.1µF
JA
VO
+ T
OUT
β
A
NOTES:
1. NC = NO CONNECT
2. TP = TEST PIN (DO NOT CONNECT)
to GND. The circuit in Figure 30
GND
NC
TP
1
2
3
4
(Not to Scale)
ADR43x
TOP VIEW
8
7
6
5
TP
COMP
V
TRIM
OUT
0.1µF
(2)
(3)