Datasheet

ADA4830-1 Data Sheet
Rev. 0 | Page 10 of 16
THEORY OF OPERATION
CORE AMPLIFIER
At the core of the ADA4830-1 is a high speed, rail-to-rail op
amp that is built on a 0.35 μm CMOS process. Together with the
core amplifier, the ADA4830-1 combines four highly matched
on-chip resistors into a difference amplifier function. Common-
mode range extension at its inputs is achieved by employing a
resistive attenuator. The closed-loop differential to single-ended
gain of the video channel is internally fixed at 0.5 V/V (−6 dB)
to ensure compatibility with video decoders whose input range
is constrained to 1 V p-p or less. The transfer function of the
ADA4830-1 is





 

2
 

where:
V
OUT
is the voltage at the output pin, VOUT.
V
IN+
and V
IN−
are the input voltages at Pin INP and Pin INN,
respectively.
V
REF
is the voltage at the VREF pin.
OVERVOLTAGE (SHORT TO BATTERY)
PROTECTION
Robust inputs guarantee that sensitive internal circuitry is not
subjected to extreme voltages or currents during a stressful
event. A short to battery condition usually consists of a voltage
on either input (or both inputs) that is significantly higher than
the power supply voltage of the amplifier. Duration may vary
from a short transient to a continuous fault.
The ADA4830-1 can withstand voltages of up to 18 V on the
inputs. Critical internal nodes are protected from exposure to
high voltages by circuitry that clamps the inputs at a safe level
and limits internal currents. This protection is available whether
the device is enabled or disabled, even when the supply voltage
is removed.
SHORT TO BATTERY OUTPUT FLAG
The short to battery output flag (STB pin) is functionally
independent of the short to battery protection. Its purpose is
to indicate an overvoltage condition on either input. Because
protection is provided passively, it is always available; the flag
merely indicates the presence or absence of a fault condition.
ESD PROTECTION
All pins on the ADA4830-1 are protected with internal ESD
protection structures connected to the power supply pins (+VS
and GND). These structures provide protection during the
handling and manufacturing process.
The inputs (INN and INP) of the ADA4830-1 can be exposed
to dc voltages well above the supply voltage; therefore, conven-
tional ESD structure protection cannot be used.
The ADA4830-1 employs Analog Devices, Inc., proprietary
ESD devices at the input pins (INN, INP) to allow for a wide
common-mode voltage range and ESD protection well beyond
the handling and manufacturing requirements.