LT1802CS datasheet(15/20 Pages) LINER

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LT1801/LT1802

18012fb

voltage is at half of either supply voltage (or the maximum

swing is less than 1/2 supply voltage). PDMAX is given by:

PDMAX = (VS • ISMAX) + (VS/2)2/RL

Example: An LT1801 in an SO-8 package operating on

±5V

supplies and driving a 50

Ω load, the worst-case power

dissipation is given by:

PDMAX = (10 • 4.5mA) + (2.5)2/50 = 0.045 + 0.125

= 0.17W

If both amplifiers are loaded simultaneously, then the total

power dissipation is 0.34W.

The maximum ambient temperature that the part is al-

lowed to operate is:

TA = TJ – (PDMAX • 190°C/W)

= 150

°C – (0.34W • 190°C/W) = 85°C

Input Offset Voltage

The offset voltage will change depending upon which input

stage is active. The PNP input stage is active from the

negative supply rail to 1.2V from the positive supply rail,

then the NPN input stage is activated for the remaining input

range up to the positive supply rail during which the PNP

stage remains inactive. The offset voltage is typically less

than 75

µV in the range that the PNP input stage is active.

Input Bias Current

The LT1801/LT1802 employ a patent-pending technique

to trim the input bias current to less than 250nA for the

input common mode voltage of 0.2V above negative

supply rail to 1.2V of the positive rail. The low input offset

voltage and low input bias current of the LT1801/LT1802

provide precision performance especially for high source

impedance applications.

Output

The LT1801/LT1802 can deliver a large output current, so

the short-circuit current limit is set around 50mA 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 several

hundred mA and the total supply voltage is less than

12.6V, the absolute maximum rating, no damage will

occur to the device.

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 10mA. If the amplifier is

severely overdriven, an external resistor should be used to

limit the overdrive current.

The LT1801/LT1802’s input stages are also protected

against a large differential input voltage of 1.4V or higher

by a pair of back-back diodes D5/D8 to prevent the emitter-

base breakdown of the input transistors. The current in these

diodes should be limited to less than 10mA when they are

active. The worst-case differential input voltage usually

occurs when the input is driven while the output is shorted

to ground in a unity gain configuration. In addition, the

amplifier is protected against ESD strikes up to 3kV on all

pins by a pair of protection diodes on each pin that are

connected to the power supplies as shown in Figure 1.

APPLICATIO S I FOR ATIO

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