LT1366/LT1367

LT1368/LT1369



1366fb

Technology’sproprietarycomplementarybipolarprocess,

which ensures very similar DC and AC characteristics for

the output devices Q24 and Q26.

AsimplecomparatorQ5steerscurrentfromcurrentsource

is within about 1.3V from the positive supply, Q5 diverts

current for the NPN differential pair Q3/Q4.

The collector currents of the two input pairs are combined

in the second stage, consisting of Q7 through Q11. Most

of the voltage gain in the amplifier is contained in this

stage. Differential amplifier Q14/Q15 buffers the output

of the second stage, converting the output voltage to dif-

ferential currents. The differential currents pass through

current mirrors D4/Q17 and D5/Q16, and are converted to

differential voltages by Q18 and Q19. These voltages are

also buffered and applied to the output Darlington pairs

Q23/Q24 and Q25/Q26. Capacitors C1 and C2 form local

feedback loops around the output devices, lowering the

output impedance at high frequencies.

Input Offset Voltage

Since the amplifier has two input stages, the input offset

voltage changes depending upon which stage is active.

Theinputoffsetsarerandom,butboundedvoltages.When

the amplifier switches between stages, offset voltages

may go up, down, or remain flat; but will not exceed the

guaranteed limits. This behavior is illustrated in three

distribution plots of input offset voltage in the Typical

Performance Characteristics section.

Overdrive Protection

Two circuits prevent the output from reversing polarity

when the input voltage exceeds the common mode range.

When the noninverting input exceeds the positive supply

by approximately 300mV, the clamp transistor Q12 (Fig-

ure 1) turns on, pulling the output of the second stage

low, which forces the output high. For inputs below the

negative supply, diodes D1 and D2 turn on, overcoming

the saturation of the input pair Q1/Q2.

When overdriven, the amplifier draws input current that

exceeds the normal input bias current. Figures 2 and 3

show some typical overdrive currents as a function of

input voltage. The input current must be less than 1mA of

positive overdrive or less than 7mA of negative overdrive,

for the phase reversal protection to work properly. When

the amplifier is severely overdriven, an external resistor

should be used to limit the overdrive current. In addition

to overdrive protection, the amplifier is protected against

ESD strokes up to 4kV on all pins.

applicaTions inForMaTion

COMMON MODE VOLTAGE RELATIVE TO

POSITIVE SUPPLY (mV)

–500

0

20

40

60

80

–300

LT1366 F02

100

100

110

90

70

50

30

10

300

500

T = –55°C

T = 25°C

T = 85°C

T = 70°C

MEASURED AS A

FOLLOWER

–

+

Figure 2. Input Bias Current vs Common Mode Voltage

COMMON MODE VOLTAGE RELATIVE TO

NEGATIVE SUPPLY (mV)

–800

–110

–90

–70

–50

–30

–600

–400

LT1366 F03

–200

–10

0

–20

–40

–60

–80

–100

200

T = –55°C T = 25°C

T = 85°C

–

+

T = 70°C

MEASURED AS A FOLLOWER

Figure 3. Input Bias Current vs Common Mode Voltage