LT6201 datasheet(14/26 Pages) AD

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LTC6246/LTC6247/LTC6248

Rev C

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APPLICATIONS INFORMATION

Circuit Description

TheLTC6246/LTC6247/LTC6248haveaninputandoutput

signal range that extends from the negative power supply

to the positive power supply. Figure 1 depicts a simplified

schematic of the amplifier. The input stage is comprised

of two differential amplifiers, a PNP stage, Q1/Q2, and an

NPN stage, Q3/Q4 that are active over different common

mode input voltages. The PNP stage is active between

the negative supply to nominally 1.2V below the posi-

tive supply. As the input voltage approaches the positive

supply, the transistor Q5 will steer the tail current, I1, to

the current mirror, Q6/Q7, activating the NPN differential

pair and the PNP pair becomes inactive for the remain-

ing input common mode range. Also, at the input stage,

devices Q17 to Q19 act to cancel the bias current of the

PNP input pair. When Q1/Q2 are active, the current in

Q16 is controlled to be the same as the current in Q1 and

Q2. Thus, 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 to Q19 to cancel

the base current of the input devices Q1/Q2. A pair of

complementarycommonemitterstages, Q14/Q15,enable

the output to swing from rail-to-rail.

Figure 1. LTC6246/LTC6247/LTC6248 Simplified Schematic Diagram

–IN: Inverting Input of Amplifier. Valid input range from V–

to V+.

+IN: Non-Inverting Input of Amplifier. Valid input range

from V– to V+.

V+ : Positive Supply Voltage. Allowed applied voltage

ranges from 2.5V to 5.25V when V– = 0V.

V–:NegativeSupplyVoltage.Typically0V.Thiscanbemade

a negative voltage as long as 2.5V ≤ (V+ – V–) ≤ 5.25V.

SHDN: Active Low Shutdown. Threshold is typically 1.1V

referenced to V–. Floating this pin will turn the part on.

OUT:AmplifierOutput.Swingsrail-to-railandcantypically

source/sink over 50mA of current at a total supply of 5V.

PIN FUNCTIONS

624678 F01

Q15

ESDD5

Q14

BUFFER

AND

OUTPUT BIAS

Q13

Q12

V–

Q11

Q10

VBIAS

Q19

Q18

Q17

ESDD2

V–

ESDD1

V+

ESDD4

V–

ESDD3

V+

Q16

V–

V+

+IN

–IN

ESDD6

OUT

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