6090FE Просмотр технического описания (PDF) - Linear Technology
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6090FE Datasheet PDF : 24 Pages
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LTC6090
Applications Information
General
The LTC6090 high voltage operational amplifier is designed
in a Linear Technology proprietary process enabling a rail-
to-rail output stage with a 140V supply while maintaining
precision, low offset, and low noise.
Power Supply
The LTC6090 works off single or split supplies. Split sup-
plies can be balanced or unbalanced. For example, two
±70V supplies can be used, or a 100V and –40V supply
can be used. For single supply applications place a high
quality surface mount ceramic 0.1µF bypass capacitor
between the supply pins close to the part. For dual supply
applications use two high quality surface mount ceramic
capacitors between V+ to ground, and V– to ground located
close to the part. When using split supplies, supply se-
quencing does not cause problems.
Input Protection
As shown in the block diagram, the LTC6090 has a com-
prehensive protection network to prevent damage to the
input devices. The current limiting resistors and back to
back diodes are to keep the inputs from being driven apart.
The voltage-current relationship combines exponential
and resistive until the voltage difference between the pins
reach 12V.
At that point the Zeners turn on. Additional current into
the pins will snap back the input differential voltage to 9V.
In the event of an ESD strike between an input and V–, the
voltage clamps and ESD device fire providing a current
path to V– protecting the input devices.
The input pin protection is designed to protect against
momentary ESD events. A repetitive large fast input swing
(>5.5V and <20ns rise time) will cause repeated stress on
the MOSFET input devices. When in such an application,
anti-parallel diodes (1N4148) should be connected between
the inputs to limit the swing.
Output Range
To get full benefit of the output drive, the feedback resistor
should be chosen carefully. Consider an amplifier with
AV = –50 and a 5k feedback resistor. A 1V input will cause
the output to rise to 50V. Since +IN is at the same potential
as –IN, a current of 10mA will flow through the feedback
resistor limiting the ability of the amplifier to drive a load.
A better choice is a 50k feedback resistor reducing the
current in the feedback resistor to 1mA.
Interfacing to Low Voltage Circuits
The COM pin is provided to set a common signal ground
for communication to a microprocessor or other low
voltage logic circuit. The COM pin should be tied to the
low voltage ground as shown in Figure 1. If left floating,
the internal resistive voltage divider will cause the COM
pin to rise 30% above mid-supply. The COM, OD, and
TFLAG pins are protected from overvoltage by internal
Zener diodes and current limiting resistors. Care should be
taken to observe the absolute maximum voltage between
the COM, OD and TFLAG pins which are limited ≤6V with
respect to COM.
Output Disable
The OD pin is an active low disable with an internal 2MΩ
resistor that will pull up the OD pin enabling the output
stage. The OD pin voltage is limited by an internal Zener
diode. When the OD pin is brought low to the COM pin,
the output stage is disabled, leaving the bias and input
circuits enabled. This results in 680μA (typical) standby
current through the device. The OD pin can be directly
connected to the low voltage driving circuitry or an open
drain NMOS device can be used as shown in Figure 1.
6090fa
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