10kW

OPA177

100W

100W

1/2 REF200

1/2 REF200

V+

R

G

INA129

Ref

V

O

V

IN

V

IN

+

10mV

±

Adjustment Range

V-

100 A

m

100 A

m

-

G = 1 +

49.4 kW

¾

R

G

G = 1 +

50 kW

¾

R

G

INA128-HT, INA129-HT

www.ti.com

SBOS501F – JANUARY 2010 – REVISED FEBRUARY 2015

Typical Application (continued)

9.2.2 Detailed Design Procedure

9.2.2.1 Setting the Gain

INA128-HT:

(1)

INA129-HT:

(2)

Commonly used gains and resistor values are shown in Figure 20.

The 50-k

Ω term in Equation 1 (49.4-kΩ in Equation 2) comes from the sum of the two internal feedback resistors

of A1 and A2. These on-chip metal film resistors are laser trimmed to accurate absolute values. The accuracy

and temperature coefficient of these internal resistors are included in the gain accuracy and drift specifications of

the INA128-HT and INA129-HT.

to gain accuracy and drift can be directly inferred from Equation 2. Low resistor values required for high gain can

make wiring resistance important. Sockets add to the wiring resistance which will contribute additional gain error

(possibly an unstable gain error) in gains of approximately 100 or greater.

9.2.2.2 Dynamic Performance

Figure 2 shows that, despite its low quiescent current, the INA128-HT and INA129-HT achieve wide bandwidth,

even at high gain. This is due to the current-feedback topology of the input stage circuitry. Settling time also

remains excellent at high gain.

9.2.2.3 Offset Trimming

The INA128-HT and INA129-HT are laser trimmed for low offset voltage and offset voltage drift. Most

applications require no external offset adjustment. Figure 21 shows an optional circuit for trimming the output

offset voltage. The voltage applied to Ref terminal is summed with the output. The operational amplifier buffer

provides low impedance at the Ref terminal to preserve good common-mode rejection.

(1)

OPA177 and REF200 are not tested or characterized at 210°C.

Figure 21. Optional Trimming of Output Offset Voltage

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