LTC6090/LTC6090-5
12
6090fe
For more information www.linear.com/LTC6090
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.
Feedback Resistor Selection
To get the most accuracy, 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 Figure 1. Low Voltage Interface
APPLICATIONS INFORMATION
rise to 50V, causing 10mA to flow through the feedback
resistor. The power dissipated in the output stage will
create thermal feedback to the input stage potentially
causing shifts in offset voltage. 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 volt-
age 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. Extra care should
be taken to observe the absolute maximum voltage limits
between (OD and COM) and between (TFLAG and COM).
Voltage limits between these pins must remain between
–3V and 7V.
6090 F01
OD
COM
LTC6090
TFLAG
10k
LOW VOLTAGE
SUPPLY
TIE TO LOW
VOLTAGE GROUND
TO LOW
VOLTAGE
CONTROL
TO LOW
VOLTAGE
CONTROL
6k
200k
V+
V–
V–
2M
V+
2M
2M
10k
6k 500Ω