EC5821 datasheet(3/11 Pages) E-CMOS

3 / 11 page

10MHz, Low Power, CMOS,

Rail-to-Rail Operational Amplifier

EC5821

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

3K29N-Rev.P001

Page 3 of 11

Rail-to-Rail Input

The input common-mode range of EC55821 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 EC5821 series can typically swing to

less than 10mV from supply rail in light resistive loads (>100k ), and 60mV of supply rail in moderate resistive

loads (10k ).

Capacitive Load Tolerance

The EC5821 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, there by preserving the phase margin in

the over all 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

EC5821 Fiches technique(PDF) 3 Page - E-CMOS Corporation