Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsAD22057RZ

FUNCTIONAL BLOCK DIAGRAM

AD22057

OUT

GND

IN+

IN–

OFS A1

REV. A

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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.

Single-Supply Sensor

Interface Amplifier

AD22057

GENERAL DESCRIPTION

The AD22057 is a single-supply difference amplifier for ampli-

fying and low-pass filtering small differential voltages (typically

100 mV FS at a gain of 40) from sources having a large common-

mode voltage.

Supply voltages from +3.0 V to +36 V can be used. The input

common-mode range extends from below ground to +24V using

FEATURES

Gain of ⴛ20. Alterable from ⴛ1 to ⴛ160

Input CMR from Below Ground to 6ⴛ (V

– 1 V)

Output Span 20 mV to (V

– 0.2) V

1-, 2-, 3-Pole Low-Pass Filtering Available

Accurate Midscale Offset Capability

Differential Input Resistance 400 k⍀

Drives 1 k⍀ Load to +4 V Using V

= +5 V

Supply Voltage: +3.0 V to +36 V

Transient Spike Protection and RFI Filters Included

Peak Input Voltage (40 ms): 60 V

Reversed Supply Protection: –34 V

Operating Temperature Range: –40ⴗC to +125ⴗC

APPLICATIONS

Current Sensing

Motor Control

Interface for Pressure Transducers, Position Indicators,

Strain Gages, and Other Low Level Signal Sources

Accelerometers

a +5 V supply with excellent rejection of this common-mode

voltage. This is achieved by the use of a special resistive attenua-

tor at the input, laser trimmed to a very high differential balance.

Provisions are included for optional low-pass filtering and gain

adjustment. An accurate midscale offset feature allows bipolar

signals to be amplified.

AD22057

SINGLE-POLE LOW-PASS FILTERING, GAIN: 40

POWER

DARLINGTON

100mV

200kV

+5V

ANALOG OUTPUT

4V PER AMP

CORNER FREQUENCY

= 0.796Hz-mF

ANALOG GROUND

SOLENOID

LOAD

(CAR BATTERY)

CMOS DRIVER

CHASSIS

Figure 1. Typical Application Circuit for a Current Sensor Interface

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Summary of content (8 pages)

PAGE 1
a Single-Supply Sensor Interface Amplifier AD22057 FEATURES Gain of ⴛ20. Alterable from ⴛ1 to ⴛ160 Input CMR from Below Ground to 6ⴛ (VS – 1 V) Output Span 20 mV to (VS – 0.2) V 1-, 2-, 3-Pole Low-Pass Filtering Available Accurate Midscale Offset Capability Differential Input Resistance 400 k⍀ Drives 1 k⍀ Load to +4 V Using VS = +5 V Supply Voltage: +3.
PAGE 2
AD22057–SPECIFICATIONS (T = +25ⴗC, V = +5 V, V A S CM = 0, RL = 10 k⍀ unless otherwise noted) Parameter Comments Test Conditions Min INPUTS (PINS 1 AND 8) +CMR CMR CMRRLF CMRRHF RINCM RMATCH RINDIFF Positive Common-Mode Range Negative Common-Mode Range Common-Mode Rejection Ratio Common-Mode Rejection Ratio Common-Mode Input Resistance Matching of Resistances Differential Input Resistance TA = TMIN to TMAX TA = TMIN to +85°C f ≤ 10 Hz f = 1 kHz Pin 1 or Pin 8 to Pin 2 –1.
PAGE 3
AD22057 ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATIONS Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . +3.0 V to +36 V Peak Input Voltage (40 ms) . . . . . . . . . . . . . . . . . . . . . . +60 V VOFS (Pin 7 to Pin 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +20 V Reversed Supply Voltage Protection . . . . . . . . . . . . . . . –34 V Operating Temperature . . . . . . . . . . . . . . . . –40°C to +125°C Storage Temperature . . . . . . . . . . . . . . . . . .
PAGE 4
AD22057 Figure 3 shows a general method for trimming the gain, either upward or downward, by an amount dependent on the resistor, R. The gain range, expressed as a percentage of the overall gain, is given by (10 MΩ/R)%. Thus, the adjustment range would be ± 2% for R = 5 MΩ; ± 10% for R = 1 MΩ, etc. ANALOG OUTPUT +IN VDM OFS +VS OUT AD22057 –IN GND A1 A2 R (SEE TEXT) VCM 6GAIN ADJUST 20kV MIN Increasing the Gain.
PAGE 5
AD22057 frequency will increase; it should be calculated using the parallel sum of the resistor and 100 kΩ. ANALOG OUTPUT CORNER FREQUENCY = +IN OFS +VS OUT VDM AD22057 –IN GND A1 1 2pC 3 100kV A three-pole filter (with roll-off 60 dB/decade) can be formed by adding a passive RC network at the output forming a real pole.
PAGE 6
AD22057 To produce a full-scale output of +4 V, a gain ×40 is used, adjustable by ±5% to absorb the tolerance in the sense resistor. There is sufficient headroom to allow at least a 10% overrange (to +4.4 V). The roughly triangular voltage across the sense resistor is averaged by a single-pole low-pass filter, here set with a corner frequency of fC = 3.6 Hz, which provides about 30 dB of attenuation at 100 Hz.
PAGE 7
AD22057 APPLICATION HINTS Frequency Compensation As are all closed-loop op amp circuits, the AD22057 is sensitive to capacitive loading at its output. However, the AD22057 is sensitive at higher output voltages due to nonlinear effects in the rail-to-rail design of the buffer amplifier (A2). In this amplifier the output stage gain increases with increasing output voltage. This behavior does not affect dc parameters such as gain accuracy or linearity; however, it can compromise ac stability.
PAGE 8
AD22057 A unique method of feedback around A1, provided by R9 and R7, sets the closed-loop gain of the preamplifier to ×10 (from the input pins). The feedback network is balanced by the inclusion of R6 and R8. The small value of R7 results in a more practical value for R9 (which would have to be 2 MΩ if the feedback were taken directly to the inputs of A1). R8 is not directly connected to ground, but to an optional voltage of one half that is applied to Pin 7 (OFS).