ada4528-1 Analog Devices, Inc., ada4528-1 Datasheet - Page 15

• Manufacturer Part Number: ada4528-1
• Description: Precision, Ultralow Noise, Rrio, Zero-drift Op Amp Ada4528-1
• Manufacturer: Analog Devices, Inc.

APPLICATIONS INFORMATION
The ADA4528-1 is a precision, ultralow noise, zero-drift opera-
tional amplifier that features a patented chopping technique. This
chopping technique offers ultralow input offset voltage of 0.3 μV
typical and input offset voltage drift of 0.002 μV/
Offset voltage errors due to common-mode voltage swings and
power supply variations are also corrected by the chopping tech-
nique, resulting in a typical CMRR figure of 158 dB and a PSRR
figure of 150 dB at 2.5 V supply voltage. The ADA4528-1 has low
broadband noise of 5.6 nV/√Hz (at f = 1 kHz, A
2.5 V) and no 1/f noise component. These features are ideal for
amplification of low level signals in dc or subhertz high
precision applications.
INPUT PROTECTION
The ADA4528-1 has internal ESD protection diodes that are
connected between the inputs and each supply rail. These diodes
protect the input transistors in the event of electrostatic dis-
charge 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. Refer to Table 4
in the Absolute Maximum Ratings section.
When either input exceeds one of the supply rails by more than
300 mV, these ESD diodes become forward-biased and large
amounts of current begin to flow through them. Without current
limiting, this excessive fault current causes permanent damage
to the device. If the inputs are expected to be subject to overvoltage
conditions, insert a resistor in series with each input to limit the
input current to 10 mA maximum. However, consider the resistor
thermal noise effect on the entire circuit.
At a 5 V supply voltage, the broadband voltage noise of the
ADA4528-1 is approximately 6 nV/√Hz (at unity gain), and a
1 kΩ resistor has thermal noise of 4 nV/√Hz. Adding a 1 kΩ
resistor increases the total noise by 30% root sum square (rss).
RAIL-TO-RAIL INPUT AND OUTPUT
The ADA4528-1 features rail-to-rail input and output with a
supply voltage from 2.2 V to 5.5 V. Figure 56 shows the input
and output waveforms of the ADA4528-1 configured as a unity-
gain buffer with a supply voltage of ±2.5 V and a resistive load
of 10 kΩ. With an input voltage of ±2.5 V, the ADA4528-1 allows
the output to swing very close to both rails. Additionally, it does
not exhibit phase reversal.
V
= +100, V
o
C typical.
SY
=
Rev. 0 | Page 15 of 20
NOISE CONSIDERATIONS
1/f noise
1/f noise, also known as pink noise or flicker noise, is inherent
in semiconductor devices and increases as frequency decreases.
At low frequency, 1/f noise is a major noise contributor and causes
a significant output voltage offset when amplified by the noise
gain of the circuit. However, the ADA4528-1 eliminates the 1/f
noise internally, thus making it an excellent choice for dc or
subhertz high precision applications. The 0.1 Hz to 10 Hz am-
plifier voltage noise is only 97 nV p-p (A
supply voltage.
The low frequency 1/f noise appears as a slow varying offset to
the ADA4528-1 and is greatly reduced by the chopping technique.
This allows the ADA4528-1 to have a much lower noise at dc
and low frequency in comparison to standard low noise amplifiers
that are susceptible to 1/f noise. Figure 45 and Figure 48 show
the voltage noise density of the amplifier with no 1/f noise.
Source Resistance
The ADA4528-1 is one of the lowest noise zero drift amplifiers
with 5.6 nV/√Hz of broadband noise at 1 kHz (V
A
important to consider the input source resistance of choice to
maintain a total low noise. The total input referred broadband
noise (e
three types of noise: input voltage noise, input current noise,
and thermal (Johnson) noise from the external resistors. These
uncorrelated noise sources can be summed up in a root sum
squared (rss) manner by using the following equation:
where:
e
I
R
k is the Boltzmann’s constant (1.38 × 10
T is the temperature in Kelvin (K).
n
n
S
V
is the input current noise of the amplifier (A/√Hz).
is the input voltage noise of the amplifier (V/√Hz).
is the total input source resistance (Ω).
= +100) currently available in the industry. Therefore, it is
e
N
–1
–2
–3
total = [e
N
3
2
1
0
total) from any amplifier is primarily a function of
V
A
R
SY
V
L
= 1
= 10kΩ
= ±2.5V
Figure 56. Rail-to Rail Input and Output
n
2
+ 4 kTR
S
TIME (200µs/DIV)
+ (i
V
V
IN
OUT
n
× R
S
)
2
]
1/2
−23
V
= +100) at 2.5 V of
J/K).
ADA4528-1
SY
= 2.5 V and