13

LT1803/LT1804/LT1805

180345f

APPLICATIO S I FOR ATIO

TYPICAL PERFOR A CE CHARACTERISTICS

Output Overdrive Recovery

Circuit Description

The LT1803/LT1804/LT1805 have input and output signal

ranges from the negative power supply to the positive

power supply. Figure 1 depicts a simplified schematic of

one amplifier. The input stage is comprised of two differ-

ential amplifiers, a PNP stage Q1/Q2 and an NPN stage Q3/

Q4 that are active over the different ranges of the common

mode input voltage. The PNP differential pair is active

between the negative supply and approximately 1.3V

below the positive supply. As the input voltage moves

toward the positive supply, the transistor Q5 will steer the

NPN differential pair. The PNP pair becomes inactive for

the rest of the input common mode range up to the positive

supply. Also at the input stage, devices Q18 and Q19 act

to cancel the bias current of the PNP input pair. When Q1

and Q2 are active, the current in Q16 is controlled to be the

same as the current in Q1 and Q2; therefore, the base

current of Q16 is nominally equal to the base current of the

input devices. The base current of Q16 is then mirrored by

devices Q17 through Q19 to cancel the base current of the

input devices Q1 and Q2.

A pair of complementary common emitter stages Q14/

Q15 that enable the output to swing from rail-to-rail

constructs the output stage. The capacitors C1 and C2

form the local feedback loops that lower the output

impedance at high frequency. The LT1803/LT1804/LT1805

are fabricated on Linear Technology’s proprietary high

speed complementary bipolar process.

Power Dissipation

There is a need to ensure that the die’s junction tempera-

ture does not exceed 150

The power dissipated in the IC is a function of the supply

voltage, amplifier current, output voltage and output cur-

rent. For a given supply voltage, the worst-case power

voltage drop in the amplifier product is maximized. For

example, if the amplifier is sourcing a constant current

to ground is given by:

Example: An LT1804 in an SO-8 package operating on

±5V

supplies and driving a 100

amplifier is given by:

= 0.095W

Currrent vs Supply Voltage graph.

±5V Large-Signal Response

±5V Small-Signal Response

180345 G39

1V/DIV

2V/DIV

0V

100ns/DIV

180345 G38

50mV/DIV

0V

50ns/DIV

180345 G37

2V/DIV

0V

200ns/DIV