AD8519(2003) 데이터 시트보기 (PDF) - Analog Devices
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AD8519 Datasheet PDF : 12 Pages
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AD8519/AD8529
VS = ؎2.5V
AVCC = 1
TA = +25؇C
CL = 100pF
R1
10k⍀
VIN
R4
10k⍀
R2 NODE A R3
10k⍀
4.99k⍀
R5
10k⍀
500mV
50s
D1
1N914
D2
1N914
U1
AD8519
R6
5k⍀
VIRTUAL GROUND = VCC
2
U2
VOUT
AD8519
R7
3.32k⍀
TPC 19. Large Signal Transient Response
Figure 1. Precision Full-Wave Rectifier
APPLICATIONS INFORMATION
Maximum Power Dissipation
The maximum power that can be safely dissipated by the
AD8519/AD8529 is limited by the associated rise in junction
temperature. The maximum safe junction temperature is 150∞C
for these plastic packages. If this maximum is momentarily
exceeded, proper circuit operation will be restored as soon as
the die temperature is reduced. Operating the product in the
“overheated” condition for an extended period can result in
permanent damage to the device.
Precision Full-Wave Rectifier
Slew rate is probably the most underestimated parameter
when designing a precision rectifier. Yet without a good slew
rate large glitches will be generated during the period when
both diodes are off.
Let’s examine the operation of the basic circuit (shown in
Figure 1) before considering slew rate further. U1 is set up to
have two states of operation. D1 and D2 diodes switch the
output between the two states. State one is an inverter with a
gain of +1, and state two is a simple unity gain buffer where the
output is equal to the value of the virtual ground. The virtual
ground is the potential present at the noninverting node of
the U1. State one is active when VIN is larger than the virtual
ground. D2 is on in this condition. If VIN drops below virtual
ground, D2 turns off and D1 turns on. This causes the output
of U1 to simply buffer the virtual ground and this configuration
is state two. So, the function of U1, which results from these
two states of operation, is a half wave inverter. The U2 function
takes the inverted half wave at a gain of two and sums it into the
original VIN wave, which outputs a rectified full wave.
VOUT = VIN - 2 VIN -1 < 0
This type of rectifier can be very precise if the following electrical
parameters are adhered to:
1. All passive components should be of tight tolerance, 1% resistors
and 5% capacitors.
Switching glitches are caused when D1 and D2 are both momen-
tarily off. This condition occurs every time the input signal is
equal to the virtual ground potential. When this condition occurs,
the U1 stage is taken out of the VOUT equation and VOUT is equal
to VIN ¥ R5 ¥ (R4 ʈ R1 + R2 + R3). Note that Node A should be
VIN inverted or virtual ground, but in this condition Node A is
simply tracking VIN. Given a sine wave input centered around
virtual ground, glitches are generated at the sharp negative peaks
of the rectified sine wave. If the glitches are hard to notice on an
oscilloscope, raise the frequency of the sine wave until they
become apparent. The size of the glitches is proportional to the
input frequency, the diode turn-on potential (0.2 V or 0.65 V),
and the slew rate of the op amp.
R6 and R7 are both necessary to limit the amount of bias current
related voltage offset. Unfortunately, there is no “perfect” value
for R6 because the impedance at the inverting node is altered as
D1 and D2 switch. Therefore, there will also be some unresolved
bias current related offset. To minimize this offset, use lower
value resistors or choose a FET amplifier if the optimized offset
is still intolerable.
The AD8519 offers a unique combination of speed versus power
ratio at 2.7 V single supply, small size (SC70 and SOT-23), and
low noise that make it an ideal choice for most high volume and
high precision rectifier circuits.
10؋ Microphone Preamp Meets PC99 Specifications
This circuit, while lacking a unique topology, is anything but
featureless when an AD8519 is used as the op amp. This preamp
gives 20 dB gain over a frequency range of 20 Hz to 20 kHz and
is fully PC99 compliant in all parameters including THD+N,
dynamic range, frequency range, amplitude range, crosstalk, and
so on. Not only does this preamp comply with the PC99 specifi-
cations, it far surpasses them. In fact, this preamp has a VOUT
noise of around 100 dB, which is suitable for most professional
20-bit audio systems. Referred to input noise is 120 dB. At 120 dB
THD+N in unity gain, the AD8519 is suitable for 24-bit profes-
sional audio systems. In other words, the AD8519 will not be
the limiting performance factor in audio systems despite its small
size and low cost.
2. If the application circuit requires high impedance (i.e., direct
sensor interface), then a FET amplifier is probably a better
choice than the AD8519.
3. An amp such as the AD8519, which has a great slew rate
specification, will yield the best result because the circuit involves
switching.
REV. C
–9–
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