AD8569(RevA) Ver la hoja de datos (PDF) - Analog Devices
Número de pieza
componentes Descripción
fabricante
AD8569 Datasheet PDF : 12 Pages
| |||
AD8568/AD8569/AD8570
APPLICATIONS
Theory of Operation
This family of buffers is designed to drive large capacitive loads
in LCD applications. Each has high output current drive, rail-
to-rail input/output operation and can be powered from a single
16 V supply. They are also intended for other applications where
low distortion and high output current drive are needed.
Input Overvoltage Protection
As with any semiconductor device, whenever the input exceeds
either supply voltage, attention needs to be paid to the input
overvoltage characteristics. As an overvoltage occurs, the amplifier
could be damaged, depending on the voltage level and the magnitude
of the fault current. When the input voltage exceeds either supply
by more than 0.6 V, internal pin junctions will allow current to
flow from the input to the supplies.
This input current is not inherently damaging to the device as
long as it is limited to 5 mA or less. If a condition exists using
the buffers where the input exceeds the supply by more than 0.6 V,
a series external resistor should be added. The size of the resistor
can be calculated by using the maximum overvoltage divided by
5 mA. This resistance should be placed in series with the input
exposed to an overvoltage.
Output Phase Reversal
The buffer family is immune to phase reversal. Although the device’s
output will not change phase, large currents due to input overvoltage
could damage the device. In applications where the possibility exists
of an input voltage exceeding the supply voltage, overvoltage protec-
tion should be used as described in the previous section.
Power Dissipation
The maximum allowable internal junction temperature of 150°C
limits the buffer family Maximum Power Dissipation. As the ambi-
ent temperature increases, the maximum power dissipated by the
buffer family must decrease linearly to maintain the maximum
junction temperature. If this maximum junction temperature is
exceeded momentarily, the part will still operate properly once
the junction temperature is reduced below 150°C. If the maxi-
mum junction temperature is exceeded for an extended period
of time, overheating could lead to permanent damage of the device.
The maximum safe junction temperature, TJMAX, is 150°C. Using
the following formula, we can obtain the maximum power that
the buffer family can safely dissipate as a function of temperature.
PDISS = (TJMAX – TA)/θJA
where:
PDISS = Power dissipation
TJMAX = Maximum allowable junction temp (150°C)
TA = Ambient temperature of the circuit
θJA = AD856x package thermal resistance, junction-to-ambient
The power dissipated by the device can be calculated as
PDISS = (VS – VOUT) ϫ ILOAD
where:
VS = supply voltage
VOUT = output voltage
ILOAD = output load current
Figure 1 shows the maximum power dissipation versus temperature.
To achieve proper operation, use the previous equation to calculate
PDISS for a specific package at any given temperature, or see Figure 1.
1.0
0.75
10-LEAD MSOP
6-LEAD SOT-23
0.5
0.25
0
؊35
؊15
5
25
45
65
85
AMBIENT TEMPERATURE – ؇C
Figure 1. Maximum Power Dissipation vs. Temperature
for 6- and 10-Lead Packages
THD + N
The buffer family features low total harmonic distortion. Figure 2
shows a graph of THD + N versus frequency. The Total Harmonic
Distortion plus Noise for the buffer over the entire supply range is
below 0.08%. When the device is powered from a 16 V supply, the
THD + N stays below 0.03%. Figure 2 shows the AD8568
THD + N versus frequency performance.
10
1
0.1
VS = ؎2.5V
VS = ؎8V
0.01
20
100
1k
FREQUENCY – Hz
10k 30k
Figure 2. AD8568 THD + N vs. Frequency
Short Circuit Output Conditions
The buffer family does not have internal short circuit protection
circuitry. As a precautionary measure, do not short the output
directly to the positive power supply or to ground.
It is not recommended to operate the AD856x with more than
35 mA of continuous output current. The output current can be
limited by placing a series resistor at the output of the amplifier
whose value can be derived using the following equation:
RX
≥
VS
35 mA
For a 5 V single supply operation, RX should have a minimum
value of 143 Ω.
REV. A
–9–
Share Link: 