ADA4853-3 Analog Devices, ADA4853-3 Datasheet - Page 16

• Manufacturer Part Number: ADA4853-3
• Description: Low Power, Rail-to-Rail Output, Video Op Amp with Ultralow Power
• Manufacturer: Analog Devices

Specifications of ADA4853-3

• -3db Bandwidth: 100MHz
• Slew Rate: 120V/µs
• Vos: 1mV
• Ib: 1µA
• # Opamps Per Pkg: 3
• Input Noise (nv/rthz): 22nV/rtHz
• Vcc-vee: 2.65V to 5V
• Isy Per Amplifier: 1.4mA
• Packages: CSP,SOP

ADA4853-1/ADA4853-2/ADA4853-3
CIRCUIT DESCRIPTION
The ADA4853-1/ADA4853-2/ADA4853-3 feature a high slew
rate input stage that is a true single-supply topology capable of
sensing signals at or below the minus supply rail. The rail-to-
rail output stage can pull within 100 mV of either supply rail
when driving light loads and within 200 mV when driving
150 Ω. High speed performance is maintained at supply
voltages as low as 2.65 V.
HEADROOM CONSIDERATIONS
The ADA4853-1/ADA4853-2/ADA4853-3 are designed for use
in low voltage systems. To obtain optimum performance, it is
useful to understand the behavior of the amplifiers as input and
output signals approach their headroom limits. The input
common-mode voltage range of the amplifier extends from the
negative supply voltage (actually 200 mV below this) to within
1.2 V of the positive supply voltage.
Exceeding the headroom limits is not a concern for any
inverting gain on any supply voltage, as long as the reference
voltage at the positive input of the amplifier lies within the a
input common-mode range of the amplifier.
The input stage is the headroom limit for signals approaching
the positive rail. Figure 50 shows a typical offset voltage vs. the
input common-mode voltage for the ADA4853-1/ADA4853-2/
ADA4853-3 on a 5 V supply. Accurate dc performance is
maintained from approximately 200 mV below the negative
supply to within 1.2 V of the positive supply. For high speed
signals, however, there are other considerations. As the
common-mode voltage gets within 1.2 V of positive supply, the
amplifier responds well but the bandwidth begins to drop as the
common-mode voltage approaches the positive supply. This can
manifest itself in increased distortion or settling time. Higher
frequency signals require more headroom than the lower
frequencies to maintain distortion performance.
–0.6
–0.8
–1.0
–1.2
–1.4
–1.6
–1.8
–2.0
–1.0 –0.5
Figure 50. V
V
S
= 5V
0
OS
0.5
vs. Common-Mode Voltage, V
1.0
1.5
V
CM
(V)
2.0
2.5
3.0
S
3.5
= 5 V
4.0
4.5
Rev. F | Page 16 of 20
For signals approaching the negative supply, inverting gain, and
high positive gain configurations, the headroom limit is the
output stage. The ADA4853-1/ADA4853-2/ADA4853-3 use a
common-emitter output stage. This output stage maximizes the
available output range, limited by the saturation voltage of the
output transistors. The saturation voltage increases with the
drive current that the output transistor is required to supply due
to the collector resistance of the output transistor.
As the saturation point of the output stage is approached, the
output signal shows increasing amounts of compression and
clipping. For the input headroom case, higher frequency signals
require a bit more headroom than the lower frequency signals.
Figure 27 illustrates this point by plotting the typical distortion
vs. the output amplitude.
OVERLOAD BEHAVIOR AND RECOVERY
Input
The specified input common-mode voltage of the ADA4853-1/
ADA4853-2/ADA4853-3 is 200 mV below the negative supply
to within 1.2 V of the positive supply. Exceeding the top limit
results in lower bandwidth and increased rise time. Pushing the
input voltage of a unity-gain follower to less than 1.2 V from the
positive supply leads to an increasing amount of output error as
well as increased settling time. The recovery time from input
voltages 1.2 V or closer to the positive supply is approximately
40 ns; this is limited by the settling artifacts caused by transis-
tors in the input stage coming out of saturation.
The amplifiers do not exhibit phase reversal, even for input
voltages beyond the voltage supply rails. Going more than 0.6 V
beyond the power supplies turns on protection diodes at the
input stage, greatly increasing the current draw of the devices.