LOG112 datasheet(3/14 Pages) TI

3 / 14 page

LOG112, 2112

SBOS246C

www.ti.com

ELECTRICAL CHARACTERISTICS

Boldface limits apply over the specified temperature range, TA = –5°C to +75°C.

At TA = +25°C, VS = ±5V, and ROUT = 10kΩ, unless otherwise noted.

LOG112, LOG2112

PARAMETER

CONDITION

MIN

TYP

MAX

UNITS

CORE LOG FUNCTION

VIN /VOUT Equation

VLOGOUT = (0.5V)LOG (I1/I2)V

LOG CONFORMITY ERROR(1)

Initial

1nA to 100

µA (5 decades)

0.01

0.2

100pA to 3.5mA (7.5 decades)

0.13

over Temperature

1nA to 100

µA (5 decades)

0.0001

°C

100pA to 3.5mA (7.5 decades)

0.005

°C

GAIN(2)

Initial Value

1nA to 100

µA

0.5

V/decade

Gain Error

1nA to 100

µA

0.10

±1%

vs Temperature

TMIN to TMAX

0.003

0.01

°C

INPUT, A1A and A1B, A2A, A2B

Offset Voltage

±0.3

±1.5

vs Temperature

TMIN to TMAX

±2

µV/

°C

vs Power Supply (PSRR)

VS = ±4.5V to ±18V

µV/V

Input Bias Current

±5pA

vs Temperature

TMIN to TMAX

Doubles Every 10

°C

Voltage Noise

f = 10Hz to 10kHz

µVrms

f = 1kHz

nV/

√Hz

Current Noise

f = 1kHz

fA/

√Hz

Common-Mode Voltage Range (Positive)

(V+) – 2

(V+) – 1.5

(Negative)

(V–) + 2

(V–) + 1.2

Common-Mode Rejection Ratio (CMRR)

µV/V

OUTPUT, (VLOG OUT) A2A, A2B

Output Offset, VOSO, Initial

±3

±15

vs Temperature

TMIN to TMAX

±10

µV/°C

Full-Scale Output (FSO)

VS = ±5V

(V–) + 1.2

(V+) – 1.5

Short-Circuit Current

±18

TOTAL ERROR(3)(4)

I1 or I2 remains fixed while other varies.

Initial

Min to Max

I1 or I2 = 5mA (VS ≥ ±6V)

±150

I1 or I2 = 3.5mA

±75

I1 or I2 = 1mA

±20

I1 or I2 = 100µA

±20

I1 or I2 = 10µA

±20

I1 or I2 = 1µA

±20

I1 or I2 = 100nA

±20

I1 or I2 = 10nA

±20

I1 or I2 = 1nA

±20

I1 or I2 = 350pA

±20

I1 or I2 = 100pA

±20

vs Temperature

I1 or I2 = 3.5mA

±1.2

mV/

°C

I1 or I2 = 1mA

±0.4

mV/

°C

I1 or I2 = 100µA

±0.1

mV/

°C

I1 or I2 = 10µA

±0.05

mV/

°C

I1 or I2 = 1µA

±0.05

mV/

°C

I1 or I2 = 100nA

±0.09

mV/

°C

I1 or I2 = 10nA

±0.2

mV/

°C

I1 or I2 = 1nA

±0.3

mV/

°C

I1 or I2 = 350pA

±0.1

mV/

°C

I1 or I2 = 100pA

±0.3

mV/

°C

vs Supply

I1 or I2 = 3.5mA

±3.0

mV/ V

I1 or I2 = 1mA

±0.1

mV/ V

I1 or I2 = 100µA

±0.1

mV/ V

I1 or I2 = 10µA

±0.1

mV/ V

I1 or I2 = 1µA

±0.1

mV/ V

I1 or I2 = 100nA

±0.1

mV/ V

I1 or I2 = 10nA

±0.1

mV/ V

I1 or I2 = 1nA

±0.25

mV/V

I1 or I2 = 350pA

±0.1

mV/ V

I1 or I2 = 100pA

±0.1

mV/ V

NOTES: (1) Log Conformity Error is the peak deviation from the best-fit-straight line of VO versus LOG (I1/I2) curve expressed as a percent of peak-to-peak full-

scale output. K, scale factor, equals 0.5V output per decade of input current. (2) Scale factor of core log function is trimmed to 0.5V output per decade change of

input current. (3) Worst-case Total Error for any ratio of I1/I2, as the largest of the two errors, when I1 and I2 are considered separately. (4) Total Error includes offset

voltage, bias current, gain, and log conformity. (5) Bandwidth (3dB) and transient response are a function of both the compensation capacitor and the level of input

current.

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