LTC1968 Linear Integrated Systems, LTC1968 Datasheet - Page 3

• Manufacturer Part Number: LTC1968
• Description: RMS-to-DC Converter
• Manufacturer: Linear Integrated Systems

ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are T
unless otherwise noted.
SYMBOL
Output Characteristics
OVR
Z
CMRRO
V
PSRRO
Frequency Response
f
f
Power Supplies
V
I
Shutdown Characteristics
I
I
I
V
V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The inputs (IN1, IN2) are protected by shunt diodes to GND and
V
to less than 10mA.
Note 3: The LTC1968 output (V
overdriven, either sinking or sourcing current, to the limits stated.
Note 4: The LTC1968C/LTC1968I are guaranteed functional over the
operating temperature range of – 40°C to 85°C.
Note 5: The LTC1968C is guaranteed to meet specified performance from
0°C to 70°C. The LTC1968C is designed, characterized and expected to
meet specified performance from – 40°C to 85°C but is not tested nor QA
sampled at these temperatures. The LTC1968I is guaranteed to meet
specified performance from – 40°C to 85°C.
Note 6: High speed automatic testing cannot be performed with
C
Note 7: The LTC1968 is 100% tested with DC and 10kHz input signals.
Measurements with DC inputs from 50mV to 350mV are used to calculate
the four parameters: G
have shown that the performance limits can be guaranteed with the
additional testing being performed to guarantee proper operation of all
internal circuitry.
Note 8: The LTC1968 is inherently very linear. Unlike older log/antilog
circuits, its behavior is the same with DC and AC inputs, and DC inputs are
used for high speed testing.
Note 9: The power supply rejections of the LTC1968 are measured with
DC inputs from 50mV to 350mV. The change in accuracy from V
to V
1P
– 3dB
S
SS
IH
IL
OUT
OMAX
+
TH
HYS
+
AVE
. If the inputs are driven beyond the rails, the current should be limited
www.DataSheet4U.com
+
= 10µF. The LTC1968 is 100% tested with C
= 5.5V is divided by 1V.
PARAMETER
Output Voltage Range
Output Impedance
Output Common Mode Rejection
Maximum Differential Output Swing
Power Supply Rejection
1% Additional Gain Error (Note 15)
±3dB Frequency (Note 15)
Supply Voltage
Supply Current
Supply Current
ENABLE Pin Current High
ENABLE Pin Current Low
ENABLE Threshold Voltage
ENABLE Threshold Hysteresis
ERR
, V
OOS
OUT
, V
) is high impedance and can be
IOS
and linearity error. Correlation tests
AVE
= 47nF.
A
= 25°C. V
CONDITIONS
(Note 12)
(Note 13)
Accuracy = 1%, DC Input (Note 14)
(Note 9)
IN1 = 20mV, IN2 = 0V
IN1 = 200mV, IN2 = 0V
V
V
V
ENABLE
ENABLE
ENABLE
+
= 4.5V
The
= 4.5V
= 4.5V
= 0.5V
+
= 5V, V
●
denotes specifications which apply over the full operating
OUTRTN
Note 10: Previous generation RMS-to-DC converters required nonlinear
input stages as well as a nonlinear core. Some parts specify a “DC reversal
error,” combining the effects of input nonlinearity and input offset voltage.
The LTC1968 behavior is simpler to characterize and the input offset
voltage is the only significant source of “DC reversal error.”
Note 11: Guaranteed by design.
Note 12: The LTC1968 is a switched capacitor device and the input/output
impedance is an average impedance over many clock cycles. The input
impedance will not necessarily lead to an attenuation of the input signal
measured. Refer to the Applications Information section titled “Input
Impedance” for more information.
Note 13: The common mode rejection ratios of the LTC1968 are measured
with DC inputs from 50mV to 350mV. The input CMRR is defined as the
change in V
V
measured with OUT RTN = 0V and OUT RTN = V
V
Note 14: The LTC1968 input and output voltage swings are limited by
internal clipping. However, its ∆Σ topology is relatively tolerant of
momentary internal clipping.
Note 15: The LTC1968 exploits oversampling and noise shaping to reduce
the quantization noise of internal 1-bit analog-to-digital conversions. At
higher input frequencies, increasingly large portions of this noise are
aliased down to DC. Because the noise is shifted in frequency, it becomes
a low frequency rumble and is only filtered at the expense of increasingly
long settling times. The LTC1968 is inherently wideband, but the output
accuracy is degraded by this aliased noise.
+
+
, divided by V
– 350mV.
= 2.5V, C
IOS
measured with the input common mode voltage at 0V and
+
. The output CMRR is defined as the change in V
AVE
= 10µF, V
●
●
●
●
●
●
●
●
●
●
IN
MIN
1.0
0.9
4.5
– 1
–3
10
0
= 200mV
– 0.1
–0.5
12.5
1.05
TYP
250
500
2.3
2.4
0.1
2.1
0.1
50
15
RMS
+
– 350mV divided by
, V
LTC1968
ENABLE
1000
MAX
– 0.1
250
5.5
2.7
V
16
10
+
= 0.5V
OOS
UNITS
3
µV/V
µV/V
MHz
1968f
kHz
mA
mA
kΩ
µA
µA
µA
V
V
V
V
V
V