ADA4522-2 Datasheet, PDF (20/30 Pages) Analog Devices – 55 V, EMI Enhanced, Zero Drift, Ultralow Noise, Rail-to-Rail Output Operational Amplifier

ADA4522-2/ADA4522-4
APPLICATIONS INFORMATION
The ADA4522-2/ADA4522-4 are dual/quad, ultralow noise,
high voltage, zero drift, rail-to-rail output operational amplifiers.
They feature a chopping technique that offers an ultralow input
offset voltage of 5 µV and an input offset voltage drift of 22 nV/°C
maximum for the ADA4522-2 and 25 nV/°C maximum for the
ADA4522-4. Offset voltage errors due to common-mode voltage
swings and power supply variations are also corrected by the
chopping technique, resulting in a superb typical CMRR figure
of 160 dB and a PSRR figure of 160 dB at a 30 V supply voltage.
The ADA4522-2/ADA4522-4 have wide operating voltages from
±2.25 V (or 4.5 V) to ±27.5 V (or 55 V). The devices are single
supply amplifiers, where their input voltage range includes the
lower supply rail. They also offer low voltage noise density of
5.8 nV/√Hz (at f = 1 kHz, A_V = 100) and reduced 1/f noise
component. These features are ideal for the amplification of low
level signals in high precision applications. A few examples of
such applications are weigh scales, high precision current sensing,
high voltage buffers, signal conditioning for temperature sensors,
among others.
THEORY OF OPERATION
Figure 70 shows the ADA4522-2/ADA4522-4 architecture block
diagram. It consists of an input EMI filter and clamp circuitry,
three gain stages (G_m1, G_m2, and G_m3), input and output chopping
networks (CHOP_IN and CHOP_OUT), a clock generator, offset
and ripple correction loop circuitry, frequency compensation
capacitors (C1, C2, and C3), and thermal shutdown circuitry.
An EMI filter and clamp circuit is implemented at the input
front end to protect the internal circuitry against electrostatic
discharge (ESD) stresses and high voltage transients. The ability
of the amplifier to reject EMI is explained in detail in the EMI
Rejection Ratio section.
CHOP_IN and CHOP_OUT are controlled by a clock generator
and operate at 4.8 MHz. The input baseband signal is initially
modulated by CHOP_IN. Next, CHOP_OUT demodulates the input
signal and modulates the millivolt-level input offset voltage and
1/f noise of the input transconductance amplifier, G_m1, to the
chopping frequency at 4.8 MHz. The chopping networks remove
the low frequency errors, but in return, the networks introduce
chopping artifacts at the chopping frequency. Therefore, a offset
and ripple correction loop, operating at 800 kHz, is used. This
frequency is the switching frequency of the amplifier. This
circuitry reduces chopping artifacts, allowing the ADA4522-2/
ADA4522-4 to have a high chopping frequency with minimal
artifacts.
The thermal shutdown circuit shuts down the circuit when
the die is overheated; this is explained further in the Thermal
Shutdown section.
Data Sheet
+IN x
–IN x
CHOP_IN
EMI
FILTER
AND
CLAMP
G_m1
C1
CHOP_OUT
G_m2
C2
G_m3
OUT
CLOCK
GENERATOR
OFFSET
AND RIPPLE
CORRECTION
LOOP
800kHz CLOCKS
C3
THERMAL
SHUTDOWN
4.8MHz CLOCKS
Figure 70. ADA4522-2/ADA4522-4 Block Diagram
ON-CHIP INPUT EMI FILTER AND CLAMP CIRCUIT
Figure 71 shows the input EMI filter and clamp circuit. The
ADA4522-2/ADA4522-4 have internal ESD protection diodes
(D1, D2, D3, and D4) that are connected between the inputs
and each supply rail. These diodes protect the input transistors
in the event of electrostatic discharge and are reverse biased
during normal operation. This protection scheme allows
voltages as high as approximately 300 mV beyond the rails
to be applied at the input of either terminal without causing
permanent damage. See Table 5 in the Absolute Maximum
Ratings section for more information.
The EMI filter is composed of two 200 Ω input series resistors
(R_S1 and R_S2), two common-mode capacitors (C_CM1 and C_CM2),
and a differential capacitor (C_DM). These RC networks set the
−3 dB low-pass cutoff frequencies at 50 MHz for common-
mode signals, and at 33 MHz for differential signals. After the
EMI filter, back to back diodes (D5 and D6) are added to protect
internal circuit devices from high voltage input transients. Each
diode has about 1 V of forward turn on voltage. See the Large
Signal Transient Response section for more information on the
effect of high voltage input transient on the ADA4522-2/
ADA4522-4.
As specified in the Absolute Maximum Ratings table (see Table 5),
the maximum input differential voltage is limited to ±5 V. If more
than ±5 V is applied, a continuous current larger than ±10 mA
flows through one of the back to back diodes. This current
compromises long term reliability and can cause permanent
damage to the device.
V+
D1
+IN x
R_S1
200Ω
D2
D3
C_CM1
R_S2
200Ω
C_DM
D5
D6
–IN x
D4
C_CM2
V–
Figure 71. Input EMI Filter and Clamp Circuit
Rev. B | Page 20 of 30