TS1101 Datasheet, PDF (8/11 Pages) Touchstone Semiconductor Inc – A 1uA, +2V to +25V Bidirectional Precision Current-Sense Amplifier

TS1101
external V_SENSE, op amp feedback action drives the
gate of M1 such that M1’s drain-source current is
equal to:
I_{DS M1}
V_{S NS}
RGAINA
or
I_{DS M1}
I_LOAD x R_{S NS}
RGAINA
Since M1’s drain terminal is connected to ROUT, the
output voltage of the TS1101 at the OUT terminal is,
therefore;
V_{O T}
I_LOAD x R_{S NS}
x ^{RO T}
RGAINA
When the voltage at the RS- terminal is greater than
the voltage at the RS+ terminal, the external
VSENSE voltage drop is impressed upon RGAINB.
The voltage drop across RGAINB is then converted
into a current by M2 that then produces an output
voltage across ROUT. In this design, when M1 is
conducting current (V_RS+ > V_RS- , the TS1101’s
internal amplifier holds M2 OFF. When M2 is
conducting current (V_RS- > V_RS+), the internal
amplifier holds M1 OFF. In either case, the disabled
FET does not contribute to the resultant output
voltage.
The current-sense amplifier’s gain accuracy is
therefore the ratio match of ROUT to RGAIN[A/B].
For each of the four gain options available, Table 1
lists the values for ROUT and RGAIN[A/B]. The
TS1101’s output stage is protected against input
overdrive by use of an output current-limiting circuit
of 3mA (typical) and a 7V internal clamp protection
circuit.
Table 1: Internal Gain Setting Resistors (Typical
Values)
GAIN (V/V)
25
50
100
200
RGAIN[A/B] (Ω)
400
200
100
100
ROUT (Ω)
10k
10k
10k
20k
Part Number
TS1101-25
TS1101-50
TS1101-100
TS1101-200
The SIGN Comparator Output
As shown in the TS1101’s block diagram, the design
of the TS1101 incorporated one additional feature –
an analog comparator the inputs of which monitor
the internal amplifier’s differential output voltage.
While the voltage at the TS1101’s O T terminal
Page 8
indicates the magnitude of the load current, the
TS1101’s SIGN output indicates the load current’s
direction. The SIGN output is a logic high when M1
is conducting current (V_RS+ > V_RS-). Alternatively, the
SIGN output is a logic low when M2 is conducting
current (V_RS+ < V_RS-). The SIGN comparator’s
transfer characteristic is illustrated in Figure 1.
Unlike other current-sense amplifiers that implement
a OUT/SIGN arrangement, the TS1101 exhibits no
“dead zone” at I_LOAD switchover.
Figure 1: TS1101's SIGN Comparator Transfer
Characteristic.
100
10
1
0.1
0.1
1
10
100
VSENSE (│VRS+ - VRS-│) - mV
Figure 2: SIGN Comparator Propagation Delay vs VSENSE.
TS1101DS r1p0
RTFDS