TS1109 Data Sheet
TS1109 Bidirectional Current-Sense Amplifier with Buffered Bipo-
lar Output
The TS1109 incorporates a bidirectional current-sense amplifier plus a buffered bipolar
output with an adjustable bias. The internal configuration of the TS1109 high-side cur-
rent-sense amplifier is a variation of the TS1101 bidirectional current-sense amplifier,
consuming 0.68 µA(typ) and 1.2 µA(max). The current-sense amplifier’s buffered output
consumes only 0.76 µ A(typ) and 1.3 µA(max) of supply current. With an input offset volt-
age of 150 µV(max) and a gain error of 1%(max), the TS1109 is optimized for high preci-
sion current measurements
Applications
• Power Management Systems
• Portable/Battery-Powered Systems
• Smart Chargers
• Battery Monitoring
• Overcurrent and Undercurrent Detection
• Remote Sensing
• Industrial Controls
KEY FEATURES
• Low Supply Current
• Current Sense Amplifier: 0.68 µA
• I
VDD
: 0.76 µA
• High Side Bidirectional Current Sense
Amplifier
• Wide CSA Input Common Mode Range: +2
V to +27 V
• Low CSA Input Offset Voltage: 150
µV(max)
• Low Gain Error: 1%(max)
• Two Gain Options Available:
• Gain = 20 V/V : TS1109-20
• Gain = 200 V/V : TS1109-200
• 8-Pin TDFN Packaging (3 mm x 3 mm)
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TS1109 Data Sheet
Ordering Information
1. Ordering Information
Table 1.1. Ordering Part Numbers
Ordering Part Number
TS1109-20IDT833
TS1109-200 IDT833
Description
Bidirectional current sense amplifier with buffered bipolar output
Bidirectional current sense amplifier with buffered bipolar output
Gain V/V
20
200
Note:
Adding the suffix “T” to the part number (e.g. TS1109-200IDT833T) denotes tape and reel.
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TS1109 Data Sheet
System Overview
2. System Overview
2.1 Functional Block Diagram
Figure 2.1. TS1109 Bidirectional Bipolar Buffered Current Sense Amplifier Block Diagram
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TS1109 Data Sheet
System Overview
2.2 Current Sense Amplifier + Output Buffer
The internal configuration of the TS1109 bidirectional current-sense amplifier is a variation of the TS1101 bidirectional current-sense
amplifier. The TS1109 current-sense amplifier is configured for fully differential input/output operation.
Referring to the block diagram, the inputs of the TS1109’s differential input/output amplifier are connected to RS+ and RS– across an
external R
SENSE
resistor that is used to measure current. At the non-inverting input of the current-sense amplifier, the applied voltage
difference in voltage between RS+ and RS– is I
LOAD
x R
SENSE
. 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 R
GAIN[A/B]
to equalize voltage at its inputs.
Thus, since the M1 PMOS source is connected to the inverting input of the internal op-amp and since the voltage drop across R
GAINA
is
the same as the external V
SENSE
, the M1 PMOS’ drain-source current is equal to:
I
DS
(M 1)
=
V
SENSE
R
GAINA
I
LOAD
×
R
SENSE
R
GAINA
I
DS
(M 1)
=
The drain terminal of the M1 PMOS is connected to the transimpedance amplifier’s gain resistor, R
OUT
, via the inverting terminal. The
non-inverting terminal of the transimpedance amplifier is internally connected to VBIAS, therefore the output voltage of the TS1109 at
the OUT terminal is:
R
OUT
V
OUT
=
V
BIAS
−
I
LOAD
×
R
SENSE
×
R
GAINA
When the voltage at the RS– terminal is greater than the voltage at the RS+ terminal, the external V
SENSE
voltage drop is impressed
upon R
GAINB
. The voltage drop across R
GAINB
is then converted into a current by the M2 PMOS. The M2 PMOS drain-source current is
the input current for the NMOS current mirror which is matched with a 1-to-1 ratio. The transimpedance amplifier sources the M2 PMOS
drain-source current for the NMOS current mirror. Therefore, the output voltage of the TS1109 at the OUT terminal is:
R
OUT
V
OUT
=
V
BIAS
+
I
LOAD
×
R
SENSE
×
R
GAINB
When M1 is conducting current (V
RS+
> V
RS–
), the TS1109’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 PMOS does not contribute to the resultant output voltage.
The current-sense amplifier’s gain accuracy is therefore the ratio match of R
OUT
to R
GAIN[A/B]
. For each of the two gain options availa-
ble, The following table lists the values for R
GAIN[A/B]
.
Table 2.1. Internal Gain Setting Resistors (Typical Values)
GAIN (V/V)
20
200
R
GAIN[A/B]
(Ω)
2k
200
R
OUT
(Ω)
40 k
40 k
Part Number
TS1109-20
TS1109-200
The TS1109 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.
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TS1109 Data Sheet
System Overview
2.3 Sign Output
The TS1109 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 the figure below. Unlike other current-sense amplifiers that implement an OUT/SIGN arrangement, the
TS1109 exhibits no “dead zone” at I
LOAD
switchover.
Figure 2.2. TS1109 Sign Output Transfer Characteristic
2.4 Selecting a Sense Resistor
Selecting the optimal value for the external R
SENSE
is based on the following criteria and for each commentary follows:
1. R
SENSE
Voltage Loss
2. V
OUT
Swing vs. Desired V
SENSE
and Applied Supply Voltage at VDD
3. Total I
LOAD
Accuracy
4. Circuit Efficiency and Power Dissipation
5. R
SENSE
Kelvin Connections
2.4.1 RSENSE Voltage Loss
For lowest IR power dissipation in R
SENSE
, the smallest usable resistor value for R
SENSE
should be selected.
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