OPA358 datasheet(8/19 Pages) TI2

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OPA361

SBOS334A − SEPTEMBER 2005 − REVISED JANUARY 2006

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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

1.5

µA. This feature is especially useful for portable video

applications, where the device is infrequently connected to

a television (TV) or other video device.

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 500

Ω 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.

12.5pF

Ω

4.22k

Ω

2.2k

Ω

2.2k

Ω

OPA361

()

3.6pF

500

Ω

Television

Figure 2. Filter Structure of the OPA361

OPA358 Datasheet(PDF) 8 Page - Texas Instruments

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