LT1818 datasheet(19/28 Pages) LINER

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LT1806/LT1807

18067fc

APPLICATIONS INFORMATION

The maximum ambient temperature that the part is

allowed to operate is:

TA = TJ – (PD(MAX) • 105°C/W)

= 150°C – (0.53W • 105°C/W) = 94°C

To operate the device at higher ambient temperature,

connect more metal area to the V – pin to reduce the thermal

resistance of the package as indicated in Table 2.

Input Offset Voltage

The offset voltage will change depending upon which

input stage is active and the maximum offset voltage is

guaranteed to less than 550μV. To maintain the precision

characteristics of the ampliﬁer, the change of VOS over the

entire input common mode range (CMRR) is limited to be

less than 550μV on a single 5V and 3V supply.

Input Bias Current

The input bias current polarity depends on a given input

common voltage at which the input stage is operating.

When the PNP input stage is active, the input bias currents

ﬂow out of the input pins. When the NPN input stage is

activated, the input bias current ﬂows into the input pins.

Because the input offset current is less than the input bias

current, matching the source resistances at the input pins

will reduce total offset error.

Output

The LT1806/LT1807 can deliver a large output current, so

the short-circuit current limit is set around 85mA to prevent

damage to the device. Attention must be paid to keep the

junction temperature of the IC below the absolute maximum

rating of 150°C (refer to the Power Dissipation section)

when the output is continuously short circuited. The output

of the ampliﬁer has reverse-biased diodes connected to

each supply. If the output is forced beyond either supply,

unlimited current will ﬂow through these diodes. If the

current is transient and limited to one hundred milliamps

or less, no damage to the device will occur.

Overdrive Protection

When the input voltage exceeds the power supplies, two

pairs of crossing diodes D1 to D4 will prevent the output

from reversing polarity. If the input voltage exceeds either

power supply by 700mV, diode D1/D2 or D3/D4 will turn

on to keep the output at the proper polarity. For the phase

reversal protection to perform properly, the input current

must be limited to less than 5mA. If the ampliﬁer is severely

overdriven, an external resistor should be used to limit

the overdrive current.

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