EC5721 datasheet(3/13 Pages) E-CMOS

3 / 13 page

1MHz, Low Power, CMOS,

Rail-to-Rail Operational Amplifier

EC5721

E-CMOS Corp. (www.ecmos.com.tw)

3L23N-Rev.P001

Page 3 of 13

Rail-to-Rail Input

The input common-mode range of EC5721 series extends 100mV beyond the supply rails (VSS-0.1V to VDD+0.1V).

This is achieved by using complementary input stage. For normal operation, inputs should be limited to this range.

Rail-to-Rail Output

Rail-to-Rail output swing provides maximum possible dynamic range at the output. This is particularly important

when operating in low supply voltages. The output voltage of EC5721 series can typically swing to less than 10mV

from supply rail in

light resistive loads (>100kΩ), and 60mV of supply rail in moderate resistive loads (10kΩ).

Capacitive Load Tolerance

The EC5721 series can directly drive 250pF capacitive load in unity-gain without oscillation. Increasing the gain

enhances the

amplifier’s ability to drive greater capacitive loads. In unity-gain configurations, the capacitive load

drive can be improved by inserting an isolation resistor RISO in series with the capacitive load, as shown in Figure 2.

Figure 2. Indirectly Driving a Capacitive Load Using Isolation Resistor

The bigger the RISO resistor value, the more stable VOUT will be. However, if there is a resistive load RL in parallel

with the capacitive load, a voltage divider (proportional to RISO/RL) is formed, this will result in a gain error.

The circuit in Figure 3 is an improvement to the one in Figure 2. RF provides the DC accuracy by feed-forward the

VIN to RL. CF and RISO serve to counteract the loss of phase margin by feeding the high frequency component of the

output signal back to the

amplifier’s inverting input, thereby preserving the phase margin in the overall feedback loop.

Capacitive drive can be increased by increasing the value of CF. This in turn will slow down the pulse response.

Figure 3. Indirectly Driving a Capacitive Load with DC Accuracy

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