Pin Descriptions
8 Ld MSOP
8 Ld SOIC
PIN NAME
PIN
FUNCTION
EQUIVALENT CIRCUIT
1
VOUTA
Output
VOUT
VS+
Circuit 1
2
VINA-
Input
VIN-
VIN+
VS+
VS-
Circuit 2
3
VINA+
Input
Reference Circuit 2
4
VS-
Supply
5
VINB+
Input
6
VINB-
Input
Reference Circuit 2
7
VOUTB
Output
Reference Circuit 1
8
VS+
Supply
9
FN7008.2
May 3, 2007
Applications Information
Product Description
The EL2228 is a dual voltage feedback operational amplifier
designed especially for DMT ADSL and other applications
requiring very low voltage and current noise. It also features
low distortion while drawing moderately low supply current
and is built on Elantec's proprietary high-speed
complementary bipolar process. The EL2228 uses a
classical voltage-feedback topology which allows them to be
used in a variety of applications where current-feedback
amplifiers are not appropriate because of restrictions placed
upon the feedback element used with the amplifier. The
conventional topology of the EL2228 allows, for example, a
capacitor to be placed in the feedback path, making it an
excellent choice for applications such as active filters,
sample-and-holds, or integrators.
Single-Supply Operation
The EL2228 was designed to have a wide input and output
voltage range. This design also makes the EL2228 an
excellent choice for single-supply operation. Using a single
positive supply, the lower input voltage range is within
300mV of ground (RL = 500Ω), and the lower output voltage
range is within 875mV of ground. Upper input voltage range
reaches 3.6V, and output voltage range reaches 3.8V with a
5V supply and RL = 500Ω. This results in a 2.625V output
swing on a single 5V supply. This wide output voltage range
also allows single-supply operation with a supply voltage as
high as 28V.
Gain-Bandwidth Product and the -3dB Bandwidth
The EL2228 has a gain-bandwidth product of 40MHz while
using only 5mA of supply current per amplifier. For gains
greater than 1, their closed-loop -3dB bandwidth is
approximately equal to the gain-bandwidth product divided
by the noise gain of the circuit. For gains of 1, higher-order
poles in the amplifiers' transfer function contribute to even
higher closed loop bandwidths. For example, the EL2228
have a -3dB bandwidth of 80MHz at a gain of 1, dropping to
9MHz at a gain of 5. It is important to note that the EL2228 is
designed so that this “extra” bandwidth in low-gain
EL2228