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PDF AD8212 Data sheet ( Hoja de datos )
| Número de pieza | AD8212 | |
| Descripción | High Voltage Current Shunt Monitor | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD8212 (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
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FEATURES
Adjustable gain
High common-mode voltage range
7 V to 65 V typical
7 V to >500 V with external pass transistor
Current output
Integrated 5 V series regulator
8-lead MSOP package
Operating temperature range of −40°C to +125°C
APPLICATIONS
Current shunt measurement
Motor controls
DC-to-DC converters
Power supplies
Battery monitoring
Remote sensing
High Voltage
Current Shunt Monitor
AD8212
FUNCTIONAL BLOCK DIAGRAM
V+ VSENSE
18
AD8212
5
IOUT
BIAS
CIRCUIT
OUTPUT
CURRENT
COMPENSATION
2
COM
3
BIAS
Figure 1.
6
ALPHA
GENERAL DESCRIPTION
The AD8212 is a high common-mode voltage, current shunt
monitor. It accurately amplifies a small differential input voltage
in the presence of large common-mode voltages up to 65 V
(>500 V with an external PNP transistor).
The AD8212 is ideal for current monitoring across a shunt
resistor in applications controlling loads, such as motors and
solenoids. The current output of the device is proportional to
the input differential voltage. The user can select an external
resistor to set the desired gain. The typical common-mode
voltage range of the AD8212 is 7 V to 65 V.
Another feature of the AD8212 is high voltage operation,
which is achieved by using an external high voltage breakdown
PNP transistor. In this configuration, the common-mode range
of the AD8212 is equal to the breakdown of the external PNP
transistor. Therefore, operation at several hundred volts is easily
achieved (see Figure 23).
The AD8212 features a patented output base current compensa-
tion circuit for high voltage operation mode. This ensures that
no base current is lost through the external transistor and
excellent output accuracy is maintained regardless of common-
mode voltage or temperature.
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2007–2009 Analog Devices, Inc. All rights reserved.
1 page  
AD8212
ABSOLUTE MAXIMUM RATINGS
TOPR = −40°C to +125°C, unless otherwise noted.
Table 2.
Parameter
Supply Voltage
Continuous Input Voltage
Reverse Supply Voltage
Operating Temperature Range
Storage Temperature Range
Output Short-Circuit Duration
Rating
65 V
68 V
0.3 V
−40°C to +125°C
−40°C to +150°C
Indefinite
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
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. B | Page 4 of 16
5 Page 
AD8212
HIGH VOLTAGE OPERATION USING AN EXTERNAL
PNP TRANSISTOR
The AD8212 offers features that simplify measuring current in
the presence of common-mode voltages greater than 65 V. This
is achieved by connecting an external PNP transistor at the
output of the AD8212, as shown in Figure 23. The VCE break-
down voltage of this PNP becomes the operating common-mode
range of the AD8212. PNP transistors with breakdown voltages
exceeding 300 V are inexpensive and readily available in small
packages.
BATTERY
RSHUNT
18
AD8212
R1 R2
A1
Q1
5
Q2
VOUT
ROUT
BIAS
CIRCUIT
OUTPUT
CURRENT
COMPENSATION
2 36
RBIAS
Figure 23. High Voltage Operation Using External PNP
The AD8212 features an integrated 5 V series regulator. This
regulator ensures that at all times COM (Pin 2), which is the
most negative of all the terminals, is always 5 V less than the
supply voltage (V+). Assuming a battery voltage (V+) of 100 V,
it follows that the voltage at COM (Pin 2) is
(V+) – 5 V = 95 V
The base emitter junction of Transistor Q2, in addition to the
Vbe of one internal transistor, makes the collector of Transistor Q1
approximately equal to
95 V + 2(Vbe(Q2)) = 95 V + 1.2 V = 96.2 V
This voltage appears across external Transistor Q2. The voltage
across Transistor Q1 is
100 V – 96.2 V = 3.8 V
In this manner, Transistor Q2 withstands 95.6 V and the
internal Transistor Q1 is only subjected to voltages well below
its breakdown capability.
In this mode of operation, the supply current (IBIAS) of the
AD8212 circuit increases based on the supply range and the
RBIAS resistor chosen. For example
if
V+ = 500 V and RBIAS = 500 kΩ
IBIAS = (V+ − 5 V)/RBIAS
then,
IBIAS = (500 – 5)/500 kΩ = 990 μA
In high voltage operation, it is recommended that IBIAS remain
within 200 μA to 1 mA. This ensures that the bias circuit is
turned on, allowing the device to function as expected. At the
same time, the current through the bias circuit/regulator is
limited to 1 mA. Refer to Figure 19 and Figure 21 for IBIAS and
V+ information when using the AD8212 in a high voltage
configuration.
When operating the AD8212, as depicted in Figure 23,
Transistor Q2 can be a FET or a bipolar PNP transistor. The
latter is much less expensive, however the magnitude of IOUT
conducted to the output resistor (ROUT) is reduced by the
amount of current lost through the base of the PNP. This leads
to an error in the output voltage reading.
The AD8212 includes an integrated patented circuit, which
compensates for the output current that is lost through the base
of the external PNP transistor. This ensures that the correct
transconductance of the amplifier is maintained. The user can
opt for an inexpensive bipolar PNP, instead of a FET, while
maintaining a comparable level of accuracy.
OUTPUT CURRENT COMPENSATION CIRCUIT
The base of the external PNP, Q2, is connected to ALPHA
(Pin 6) of the AD8212. The current flowing in this path is
mirrored inside the current compensation circuit. This
current then flows in Resistor R2, which is the same value
as Resistor R1. The voltage created by this current across
Resistor R2, displaces the noninverting input of Amplifier A1
by the corresponding voltage. Amplifier A1 responds by driving
the base of Transistor Q1 so as to force a similar voltage
displacement across Resistor R1, thereby increasing IOUT.
Because the current generated by the output compensation
circuit is equal to the base current of Transistor Q2, and the
resulting displacements across Resistor R1 and Resistor R2 result
in equal currents, the increment of current added to the output
current is equivalent to the base current of Transistor Q2.
Therefore, the integrated output current compensation circuit
has corrected IOUT such that no error results from the base
current lost at Transistor Q2.
This feature of the AD8212 greatly improves IOUT accuracy and
allows the user to choose an inexpensive bipolar PNP (with low
beta) with which to monitor current in the presence of high
voltages (typically several hundred volts).
Rev. B | Page 10 of 16
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AD8212.PDF ] | |
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