AD8515

Data Sheet

Rev. E | Page 12 of 16

THEORY OF OPERATION

TheAD8515, offered in space-saving SOT-23 and SC70 packages,

is a rail-to-rail input and output operational amplifier that can

operate at supply voltages as low as 1.8 V. This product is fabri-

cated using 0.6 micron CMOS to achieve one of the best power

consumption-to-speed ratios (that is, bandwidth) in the industry.

With a small amount of supply current (less than 400 μA),

a wide unity gain bandwidth of 4.5 MHz is available for signal

processing.

The input stage consists of two parallel, complementary, differ-

ential pairs of PMOS and NMOS. The AD8515 exhibits no

phase reversal because the input signal exceeds the supply by

more than 0.6 V. Currents into the input pin must be limited

to 5 mA or less by the use of external series resistance(s). The

AD8515 has a very robust ESD design and can stand ESD

voltages of up to 4000 V.

POWER CONSUMPTION vs. BANDWIDTH

One of the strongest features of the AD8515 is the bandwidth

stability over the specified temperature range while consuming

small amounts of current. This effect is shown in Figure 2 through

Figure 4.

This product solves the speed/power requirements for many

applications. The wide bandwidth is also stable even when operated

with low supply voltages. Figure 5 shows the relationship between

the supply voltage vs. the bandwidth for the AD8515.

The AD8515 is ideal for battery-powered instrumentation and

handheld devices because it can operate at the end of discharge

voltage of most popular batteries. Table 6 lists the nominal and

end of discharge voltages of several typical batteries.

Table 6. Typical Battery Life Voltage Range

Battery

Nominal

Voltage (V)

End of Discharge

Voltage (V)

Lead-Acid

2

1.8

Lithium

2.6 to 3.6

1.7 to 2.4

NiMH

1.2

1

NiCd

1.2

1

Carbon-Zinc

1.5

1.1