LTC6102HV Linear Technology, LTC6102HV Datasheet - Page 11

• Manufacturer Part Number: LTC6102HV
• Description: Zero Drift High Side Current Sense Amplifier
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
Output Error, E
Voltage, V
The DC offset voltage of the amplifi er adds directly to the
value of the sense voltage, V
(3μV typ) and may be ignored for reasonable values of R
For very high dynamic range, this offset can be calibrated
in the system due to its extremely low drift.
Output Error, E
I
The input bias current of the LTC6102 is vanishingly small.
However, for very high resolution, or at high temperatures
where I
signifi cant.
The bias current I
internal op amp. I
Since I
For instance if I
error is –10μV.
Note that in applications where R
a voltage offset in R
I
R
external resistor R
shown in Figure 4. Under both conditions:
Adding R
range of the circuit. For less sensitive designs, R
not necessary.
Clock Feedthrough, Input Bias Current
The LTC6102 uses auto-zeroing circuitry to achieve an
almost zero DC offset over temperature, sense voltage,
and power supply voltage. The frequency of the clock
used for auto-zeroing is typically 10kHz. The term clock
feedthrough is broadly used to indicate visibility of this
B
B
IN
(+) and I
(–) and E
E
E
E
E
, the bias current error can be similarly reduced if an
OUT(VOS)
OUT(IBIAS)
OUT(IBIAS)
OUT(IBIAS)
B
B
(+) ≈ I
increases due to leakage, the current may be
IN
B
OS
OUT(IBIAS)
+
(–)
= V
as described will maximize the dynamic
= R
≈ –R
= ± R
B
OUT
OUT
(–) = I
BIAS
OS
B
OUT
B
, Due to the Amplifi er DC Offset
, Due to the Bias Currents,
IN
(+) fl ows into the positive input of the
(–) fl ows into the negative input.
OUT
• (R
OUT
(+) = (R
is 1nA and R
SENSE
((I
≈ 0. In applications where R
BIAS
• I
OUT
B
• I
(+) • (R
BIAS
, if R
OS
/R
that cancels the error due to
SENSE
IN
; I
IN
OS
SENSE
– R
)
SENSE
SENSE
. This error is very small
= I
SENSE
OUT
B
<< R
(+) – I
/R
≈ R
is 10k, the output
) is connected as
IN
IN
IN
) – I
, I
B
then,
(–)
B
B
(+) causes
(–))
SENSE
IN
+
IN
is
<
.
clock frequency in the op amp output spectrum. There are
typically two types of clock feedthrough in auto zeroed
amps like the LTC6102.
The fi rst form of clock feedthrough is caused by the
settling of the internal sampling capacitor and is input
referred; that is, it is multiplied by the internal loop gain
of the amp. This form of clock feedthrough is independent
of the magnitude of the input source resistance or the
magnitude of the gain setting resistors. The LTC6102 has
a residue clock feedthrough of less then 1μV
referred at 10kHz.
The second form of clock feedthrough is caused by the
small amount of charge injection occurring during the
sampling and holding of the amp’s input offset voltage.
The current spikes are multiplied by the impedance seen
at the input terminals of the amp, appearing at the output
multiplied by the internal loop gain of the internal op amp.
To reduce this form of clock feedthrough, use smaller
valued gain setting resistors and minimize the source
resistance at the input.
Input bias current is defi ned as the DC current into the
input pins of the op amp. The same current spikes that
cause the second form of clock feedthrough described
above, when averaged, dominate the DC input bias current
of the op amp below 70°C.
R
SENSE
LOAD
V
+
Figure 4. Second Input R Minimizes
Error Due to Input Bias Current
R
R
LTC6102/LTC6102HV
IN
IN
–
+
+IN
V
–
R
IN
LTC6102
+
=
R
+
IN
–
–
R
SENSE
–
–INS
V
OUT
–INF
V
REG
+
6102 F04
R
OUT
RMS
V
OUT
0.1μF
11
input
6102f