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2.2 Current Sense Amplifier + Output Buffer

The internal configuration of the TS1105 unidirectional and TS1106 bidirectional current-sense amplifiers are buffered variations of the

TS1100 unidirectional and TS1101 bidirectional current-sense amplifier respectively. The TS1106 current-sense amplifier is configured

for fully differential input/output operation, therefore the behavior of the TS1106 current-sense amplifier is identical for either VRS+ >

VRS– or VRS– > VRS+.

Referring to the block diagrams, the inputs of the TS1105/06’s differential input/output amplifier are connected to RS+ and RS– across

an external RSENSE resistor that is used to measure current. At the non-inverting input of the current-sense amplifier, the applied volt-

age difference in voltage between RS+ and RS– is ILOAD x RSENSE. Since the RS– terminal is the non-inverting input of the internal op-

amp, the current-sense op-amp action drives PMOS[1/2] to drive current across RGAIN[A/B] to equalize voltage at its inputs.

Thus, since the PMOS source for both M1 and M2 are connected to the inverting input of the internal op-amp and since the voltage

drop across RGAINA or RGAINB is the same as the external VSENSE, the PMOS drain-source current for either M1 or M2 is equal to:

IDS(M 1&M 2) =

VSENSE

GAIN A/B

IDS(M 1&M 2) =

ILOAD × RSENSE

GAIN A/B

The drain terminal for PMOS[1/2] is connected to the transimpedance amplifier’s gain resistor, ROUT, via the inverting terminal. The

non-inverting terminal of the transimpedance amplifier is internally connected to VBIAS, therefore the output voltage of the TS1105/06

at the OUT terminal is

VOUT = VBIAS − ILOAD × RSENSE ×

ROUT

GAIN A/B

The current-sense amplifier’s gain accuracy is therefore the ratio match of ROUT to RGAIN[A/B]. For each of the gain options available,

the table below lists the values for RGAIN[A/B]

Table 2.1. Internal Gain Setting Resistors (Typical Values)

GAIN (V/V)

RGAIN[A/B] (Ω)

ROUT (Ω)

Part Number

2 k

40 k

TS1105-20

200

40 k

TS1105-200

2 k

40 k

TS1106-20

200

40 k

TS1106-200

The TS1105/06 allows access to the inverting terminal of the transimpedance amplifier by the FILT pin, whereby a series RC filter may

be connected to reduce noise at the OUT terminal. The recommended RC filter is 4 kΩ and 0.47 μF connected in series from FILT to

GND to suppress the noise. Any capacitance at the OUT terminal should be minimized for stable operation of the buffer.

TS1105/06 Data Sheet

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