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Data Sheet
ADA4432-1/ADA4433-1
Rev. A | Page 15 of 28
THEORY OF OPERATION
short-to-ground protection are designed as fifth-order, low-pass
filters with a fixed gain of 2 that is capable of driving 2 V p-p video
signals into doubly terminated video transmission lines on a single
supply as low as 2.6 V. The filter has a 1 dB flatness of 9 MHz
and provides a typical out-of-band rejection of 45 dB at 27 MHz.
with both ac- and dc-coupled inputs and outputs, with an input
range that includes ground for use with a ground referenced
digital-to-analog converter (DAC) in a single-supply application.
To ensure accurate reproduction of ground referenced signals
without saturating the output devices, an internal offset is
added to shift the output voltage up by 200 mV.
designed for compliance with both ac- and dc-coupled inputs and
ended source and provides a fully differential output signal that
is biased at a voltage equal to half the supply voltage (+VS/2). When
the device is used with a single-ended input source, bias the
inverting input, IN, at the middle of the input voltage range
applied to the noninverting input, +IN, allowing each output
signal to swing equally around the midsupply point (see the
section). This is particularly important to maximize output
voltage headroom in low supply voltage applications.
SHORT CIRCUIT (SHORT-TO-GROUND) PROTECTION
circuits that limit the output sink or source current to 60 mA.
This short circuit protection prevents damage to t
he ADA4432-1low impedance source, or together (in the case of th
e ADA4433-1)the total sink or source current for both outputs is limited to
50 mA, which helps protect the device in the event of both outputs
being shorted to a low impedance. However, short circuit
protection does not affect the normal operation of the devices
because one output sources current, whereas the other output
sinks current when driving a differential output signal.
OVERVOLTAGE (SHORT-TO-BATTERY) PROTECTION
circuits to ensure that internal circuitry is not subjected to
extreme voltages or currents during an overvoltage event
applied to their outputs. A short-to-battery condition usually
consists of a voltage on the outputs that is significantly higher
than the power supply voltage of the amplifier. Duration can
vary from a short transient to a continuous fault.
to 18 V on the outputs. Critical internal nodes are protected from
exposure to high voltages by circuitry that isolates the output
devices from the high voltage and limits internal currents. This
protection is available whether the device is enabled or disabled,
even when the supply voltage is removed.
The output devices are disconnected when the voltage at the
output pins exceeds the supply voltage. After the overvoltage
condition is removed, internal circuitry pulls the output voltage
back within normal operating levels. The output devices are
reconnected when the voltage at the output pins falls below the
supply voltage by about 300 mV. When the devices are used with a
doubly terminated cable, the voltage sensed at the output pins is
lower than the voltage applied to the cable by the voltage drop
across the back termination resistor. The maximum voltage drop
across the back termination resistor is limited by the short-circuit
current protection; therefore, the threshold at which the over-
voltage protection responds to a voltage applied to the cable is
VTHRESH(CABLE) = +VS + ILIMITRT
where:
VTHRESH(CABLE) is the voltage applied to the cable that activates the
internal isolation circuitry.
+VS is the positive supply voltage.
ILIMIT is the internal short-circuit current limit, typically 50 mA.
RT the back termination resistance.
If the voltage applied to the cable is lower than VTHRESH(CABLE), the
voltage seen at the output pins is lower than the supply voltage,
so no overvoltage condition is detected. However, the internal
circuitry is protected by the short circuit current limit; therefore,
short to any positive voltage up to 18 V without damage.
SHORT-TO-BATTERY OUTPUT FLAG
In addition to the internal protection circuitry, the short-to-
battery output flag (STB pin) indicates an overvoltage condition
on either or both output pins. The flag is present whenever the
internal overvoltage protection is active; therefore, it is available
when the device is enabled or disabled. It is not available, however,
when the supply voltage is removed, although the internal
protection is still active. The threshold at which the short-to-
battery flag is activated and deactivated is the same as the
threshold for the protection circuitry.
Table 8. STB Pin Logic
STB Pin Output
Device State
High (Logic 1)
Overvoltage fault condition
Low (Logic 0)
Normal operation