OPA361AIDCKT Datasheet, PDF (8/17 Pages) Texas Instruments – 3V VIDEO AMPLIFIER with Internal Gain and Filter in SC70

OPA361
SBOS334A − SEPTEMBER 2005 − REVISED JANUARY 2006
OPERATING VOLTAGE
The OPA361 is fully specified from 2.5V to 3.3V over a
temperature range of −40_C to +125_C. Parameters that
vary significantly with operating voltages or temperature
are shown in the Typical Characteristics. Power-supply
pins should be bypassed with 100nF ceramic capacitors.
INPUT VOLTAGE
The input common-mode range of the OPA361 series
extends from GND to 0.55V on a 3.3V supply. The input
range is limited by the internal gain in conjunction with the
maximum output swing capability and the power-supply
voltage.
INPUT OVERVOLTAGE PROTECTION
All OPA361 pins are static-protected with internal ESD
protection diodes connected to the supplies. These diodes
will provide input overdrive protection if the current is
externally limited to 10mA.
ENABLE/SHUTDOWN
The OPA361 has a shutdown feature that disables the
output and reduces the quiescent current to less than
1.5µA. This feature is especially useful for portable video
applications, where the device is infrequently connected to
a television (TV) or other video device.
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The Enable logic input voltage is referenced to the
OPA361 GND pin. A logic level HIGH applied to the enable
pin enables the op amp. The logic levels are compatible
with 1.8V CMOS logic levels. A valid logic HIGH is defined
as > 1.3V above GND. A valid logic LOW is defined as
< 0.35V above GND. If the Enable pin is not connected,
internal pull-up circuitry will enable the amplifier.
When disabling the OPA361, internal circuitry also
disconnects the internal gain setting feedback. This
feature is in support of the TV-detection function. See the
TV-Detect Function section for more detailed information.
INTERNAL 2-POLE FILTER
The OPA361 filter is a Sallen-Key topology with a 9MHz
cutoff frequency. Figure 2 shows a detailed drawing of the
filter components. This filter allows video signals to pass
without any visible distortion, as shown in Figure 3 through
Figure 6. The video encoder embedded in the OMAP242x
processor typically samples at 54MHz. At this frequency,
the attenuation is typically 23dB, which effectively
attenuates the sampling aliases.
The internal 500Ω resistor on the input to GND converts
the output current of the OMAP2420 internal video DAC
into a voltage. It is also part of the Sallen-Key filter. Using
an external resistor to adjust the input voltage range will
also alter the filter characteristics.
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OPA361
2.2kΩ
2.2kΩ
500Ω
3.6pF
12.5pF
4.22kΩ
1kΩ
V_O 75Ω
Television
75Ω
Figure 2. Filter Structure of the OPA361
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