LTC6102HVCDD(RevB) 查看數據表（PDF） - Linear Technology

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LTC6102HVCDD
(Rev.:RevB)

Precision Zero Drift Current Sense Amplifier

Linear Technology 

LTC6102/LTC6102HV

APPLICATIONS INFORMATION

must be chosen such that the max output voltage does

not exceed the LTC6102 max output voltage rating. If the

following circuit is a buffer or ADC with limited input range,

then ROUT must be chosen so that IOUT(MAX) • ROUT is less

than the allowed maximum input range of this circuit.

In addition, the output impedance is determined by ROUT. If

the circuit to be driven has high enough input impedance,

then almost any output impedance will be acceptable.

However, if the driven circuit has relatively low input imped-

ance, or draws spikes of current, such as an ADC might

do, then a lower ROUT value may be required in order to

preserve the accuracy of the output. As an example, if the

input impedance of the driven circuit is 100 times ROUT,

then the accuracy of VOUT will be reduced by 1% since:

VOUT

= IOUT

•

ROUT

ROUT

• RIN(DRIVEN)

+ RIN(DRIVEN)

= IOUT

• ROUT

•

100

101

=

0.99

• IOUT

•

ROUT

Error Sources

The current sense system uses an amplifier and resistors

to apply gain and level shift the result. The output is then

dependent on the characteristics of the amplifier, such as

gain and input offset, as well as resistor matching.

Ideally, the circuit output is:

VOUT

=

VSENSE

•

ROUT

RIN

; VSENSE

=

RSENSE

• ISENSE

In this case, the only error is due to resistor mismatch,

which provides an error in gain only.

Output Error, EOUT, Due to the Amplifier DC Offset

Voltage, VOS

EOUT(VOS) = VOS • (ROUT/RIN)

The DC offset voltage of the amplifier adds directly to the

value of the sense voltage, VSENSE. This error is very small

(3μV typ) and may be ignored for reasonable values of RIN.

For very high dynamic range, this offset can be calibrated

in the system due to its extremely low drift.

Output Error, EOUT, Due to the Bias Currents,

IB(+) and IB(–)

The input bias current of the LTC6102 is vanishingly small.

However, for very high resolution, or at high temperatures

where IB increases due to leakage, the current may be

significant.

The bias current IB(+) flows into the positive input of the

internal op amp. IB(–) flows into the negative input.

EOUT(IBIAS) = ROUT((IB(+) • (RSENSE/RIN) – IB(–))

Since IB(+) ≈ IB(–) = IBIAS, if RSENSE << RIN then,

EOUT(IBIAS) ≈ –ROUT • IBIAS

For instance if IBIAS is 1nA and ROUT is 10k, the output

error is –10μV.

Note that in applications where RSENSE ≈ RIN, IB(+) causes

a voltage offset in RSENSE that cancels the error due to

IB(–) and EOUT(IBIAS) ≈ 0. In applications where RSENSE <

RIN, the bias current error can be similarly reduced if an

external resistor RIN(+) = (RIN – RSENSE) is connected as

shown in Figure 4. Under both conditions:

EOUT(IBIAS) = ± ROUT • IOS; IOS = IB(+) – IB(–)

Adding RIN+ as described will maximize the dynamic

range of the circuit. For less sensitive designs, RIN+ is

not necessary.

V+

RIN–

RSENSE

RIN+ +IN

LOAD

V–

+–

–INS

–INF

V+

VREG

0.1μF

LTC6102

RIN+ = RIN– – RSENSE

OUT

VOUT

ROUT

6102 F04

Figure 4. Second Input R Minimizes

Error Due to Input Bias Current

6102fb

11

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