Datasheet
LOG112, 2112
3
SBOS246D
www.ti.com
ELECTRICAL CHARACTERISTICS
Boldface limits apply over the specified temperature range, T
A
= –5°C to +75°C.
At T
A
= +25°C, V
S
= ±5V, and R
OUT
= 10kΩ, unless otherwise noted.
LOG112, LOG2112
PARAMETER CONDITION MIN TYP MAX UNITS
CORE LOG FUNCTION
V
IN
/V
OUT
Equation V
LOGOUT
= (0.5V)LOG (I
1
/I
2
)V
LOG CONFORMITY ERROR
(1)
Initial 1nA to 100µA (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 100µA 0.5 V/decade
Gain Error 1nA to 100µA 0.10 ±1%
vs Temperature T
MIN
to T
MAX
0.003 0.01 %/°C
INPUT, A
1A
and A
1B
, A
2A
, A
2B
Offset Voltage ±0.3 ±1.5 mV
vs Temperature T
MIN
to T
MAX
±2 µV/°C
vs Power Supply (PSRR) V
S
= ±4.5V to ±18V 5 20 µV/V
Input Bias Current ±5pA
vs Temperature T
MIN
to T
MAX
Doubles Every 10°C
Voltage Noise f = 10Hz to 10kHz 3 µVrms
f = 1kHz 30 nV/√Hz
Current Noise f = 1kHz 4 fA/√Hz
Common-Mode Voltage Range (Positive) (V+) – 2 (V+) – 1.5 V
(Negative) (V–) + 2 (V–) + 1.2 V
Common-Mode Rejection Ratio (CMRR) 10 µV/V
OUTPUT, (V
LOG OUT
) A
2A
, A
2B
Output Offset, V
OSO
, Initial ±3 ±15 mV
vs Temperature T
MIN
to T
MAX
±10 µV/°C
Full-Scale Output (FSO) V
S
= ±5V (V–) + 1.2 (V+) – 1.5 V
Short-Circuit Current ±18 mA
TOTAL ERROR
(3)(4)
I
1
or I
2
remains fixed while other varies.
Initial Min to Max
I
1
or I
2
= 5mA (V
S
≥ ±6V) ±150 mV
I
1
or I
2
= 3.5mA ±75 mV
I
1
or I
2
= 1mA ±20 mV
I
1
or I
2
= 100µA ±20 mV
I
1
or I
2
= 10µA ±20 mV
I
1
or I
2
= 1µA ±20 mV
I
1
or I
2
= 100nA ±20 mV
I
1
or I
2
= 10nA ±20 mV
I
1
or I
2
= 1nA ±20 mV
I
1
or I
2
= 350pA ±20 mV
I
1
or I
2
= 100pA ±20 mV
vs Temperature I
1
or I
2
= 3.5mA ±1.2 mV/°C
I
1
or I
2
= 1mA ±0.4 mV/°C
I
1
or I
2
= 100µA ±0.1 mV/°C
I
1
or I
2
= 10µA ±0.05 mV/°C
I
1
or I
2
= 1µA ±0.05 mV/°C
I
1
or I
2
= 100nA ±0.09 mV/°C
I
1
or I
2
= 10nA ±0.2 mV/°C
I
1
or I
2
= 1nA ±0.3 mV/°C
I
1
or I
2
= 350pA ±0.1 mV/°C
I
1
or I
2
= 100pA ±0.3 mV/°C
vs Supply I
1
or I
2
= 3.5mA ±3.0 mV/V
I
1
or I
2
= 1mA ±0.1 mV/V
I
1
or I
2
= 100µA ±0.1 mV/V
I
1
or I
2
= 10µA ±0.1 mV/V
I
1
or I
2
= 1µA ±0.1 mV/V
I
1
or I
2
= 100nA ±0.1 mV/V
I
1
or I
2
= 10nA ±0.1 mV/V
I
1
or I
2
= 1nA ±0.25 mV/V
I
1
or I
2
= 350pA ±0.1 mV/V
I
1
or I
2
= 100pA ±0.1 mV/V
NOTES: (1) Log Conformity Error is the peak deviation from the best-fit-straight line of V
O
versus LOG (I
1
/I
2
) 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 I
1
/I
2
, as the largest of the two errors, when I
1
and I
2
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.