AD8515AKS Analog Devices, AD8515AKS Datasheet - Page 11

• Manufacturer Part Number: AD8515AKS
• Description: 1.8 V Low Power CMOS Rail-to-rail Input/output Single Operational Amp
• Manufacturer: Analog Devices

FUNCTIONAL DESCRIPTION
The AD8515, offered in space-saving SOT-23 and SC70 pack-
ages, 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
fabricated using 0.6 micron CMOS to achieve one of the best power
consumption to speed ratios (i.e., bandwidth) in the industry. With a
small amount of supply current (less than 400 mA), a wide unity
gain bandwidth of 4.5 MHz is available for signal processing.
The input stage consists of two parallel, complementary, differential
pairs of PMOS and NMOS. The AD8515 exhibits no phase rever-
sal as 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 4,000 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 TPC 1 through
TPC 3. This product solves the speed/power requirements for
many applications. The wide bandwidth is also stable even when
operated with low supply voltages. TPC 4 shows the relationship
between the supply voltage versus the bandwidth for the AD8515.
The AD8515 is ideal for battery-powered instrumentation and
handheld devices since it can operate at the end of discharge
voltage of most popular batteries. Table I lists the nominal and
end of discharge voltages of several typical batteries.
Battery
Lead-Acid
Lithium
NiMH
NiCd
Carbon-Zinc
DRIVING CAPACITIVE LOADS
Most amplifiers have difficulty driving large capacitive loads.
Additionally, higher capacitance at the output can increase the
amount of overshoot and ringing in the amplifier’s step response
and could even affect the stability of the device. This is due to the
degradation of phase margin caused by additional phase lag from
the capacitive load. The value of capacitive load that an amplifier
can drive before oscillation varies with gain, supply voltage, input
signal, temperature, and other parameters. Unity gain is the most
challenging configuration for driving capacitive loads. The AD8515
is capable of driving large capacitive loads without any external
compensation. The graphs in Figures 1a and 1b show the amplifier’s
capacitive load driving capability when configured in unity gain of +1.
The AD8515 is even capable of driving higher capacitive loads
in inverting gain of –1, as shown in Figure 2.
REV. B
Table I. Typical Battery Life Voltage Range
Nominal Voltage (V)
2
2.6–3.6
1.2
1.2
1.5
End of Discharge
Voltage (V)
1.8
1.7–2.4
1
1
1.1
–11–
Figure 1b. Capacitive Load Driving @ C
Figure 1a. Capacitive Load Driving @ C
Figure 2. Capacitive Load Driving @ C
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
V
C
GAIN = +1
V
C
GAIN = +1
V
C
GAIN = –1
S
S
L
S
L
L
0
0
0
= 2.5V
= 50pF
= 2.5V
= 500pF
= 0.9V
= 800pF
0
0
0
0
0
0
TIME (1 s/DIV)
TIME (1 s/DIV)
0
TIME (1 s/DIV)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
AD8515
L
L
L
= 800 pF
= 500 pF
= 50 pF
0
0
0
0
0
0