The TSM103 is a specialized analog integrated circuit from STMicroelectronics that combines two operational-amplifier functions with a built-in 2.5 V voltage reference. This combination makes it particularly useful in power-supply management, feedback and control circuits, battery chargers, adapters and data-acquisition systems. By integrating the reference and amplifier functions, the device can reduce component count, PCB area and design complexity.

What is TSM103?

The TSM103 is a monolithic dual operational amplifier and voltage-reference IC. One amplifier is independent, while the non-inverting input of the second amplifier is internally connected to a fixed 2.5 V reference. This architecture is especially useful when an analog signal must be amplified, monitored or compared against a stable reference.

Important lifecycle note: STMicroelectronics identifies the original TSM103/A as “not for new design” and states that it is replaced by TSM103W. For a new product, designers should evaluate the active TSM103W family and the exact ordering code.

Key Features

· Dual operational-amplifier architecture

· Integrated fixed 2.5 V voltage reference

· Typical input offset voltage of 0.5 mV

· Low supply current: 350 µA per amplifier at VCC = 5 V

· Unity-gain bandwidth of approximately 0.9 MHz

· Input common-mode range includes ground

· Output swing from approximately 0 V to VCC − 1.5 V

· Wide supply range: 3 V to 32 V single supply, or ±1.5 V to ±16 V

· TSM103W reference precision options of ±0.4% or ±0.7%

· Reference sink-current capability from 1 mA to 100 mA

· Typical reference output impedance of 0.2 Ω

· 1.5 kV ESD protection

TSM103 Specifications

Parameter	Typical / specified value
Device function	Dual operational amplifier + 2.5 V reference
Supply voltage	3 V to 32 V single supply; ±1.5 V to ±16 V
Input offset voltage	0.5 mV typ.
Supply current	350 µA/op. typ. at VCC = 5 V
Unity-gain bandwidth	0.9 MHz typ.
Output voltage swing	0 V to VCC − 1.5 V
Input common-mode range	Includes ground
Reference output voltage	2.5 V fixed
Reference precision (TSM103W)	±0.4% or ±0.7%
Reference output impedance	0.2 Ω typ.
Reference sink current	1 to 100 mA
ESD protection	1.5 kV
Operating temperature	−40°C to +105°C for listed industrial versions
Package	SO-8 for active TSM103W versions

Pin Configuration

For the SO-8 package, the functional pin assignment is:

Pin	Function
1	Output 1
2	Inverting input 1
3	Non-inverting input 1
4	VCC−
5	Non-inverting input 2 / internal 2.5 V reference connection
6	Inverting input 2
7	Output 2
8	VCC+

How the TSM103 Works

The first amplifier can be used like a conventional op-amp for signal conditioning, amplification, filtering or feedback processing. The second amplifier has its non-inverting input tied internally to the 2.5 V reference. A resistor divider or sensing network can therefore provide a voltage to the inverting input, allowing the amplifier to generate an error signal related to the difference between the sensed voltage and the internal reference.

In a regulated power supply, this error signal can be passed to a PWM controller, compensation network or subsequent control stage. The controller then adjusts the switching action to maintain the required output voltage or operating condition.

TSM103 in SMPS and Power-Supply Feedback

A particularly important application is secondary-side feedback in isolated power supplies. The regulated output can be sampled using a resistor divider and compared with the internal 2.5 V reference. The amplifier output provides the error information required by the regulation loop.

This makes the TSM103/TSM103W concept useful in AC-DC adapters, flyback converters, auxiliary supplies, DC-DC converters and battery chargers. Actual loop design must account for compensation, optocoupler characteristics where applicable, amplifier gain and bandwidth, reference tolerance, resistor tolerance and output loading.

Example: Setting a Regulated Output

For a basic resistor divider, the sensed voltage is V_SENSE = V_OUT × R2/(R1 + R2). Regulation occurs when V_SENSE is approximately equal to the 2.5 V reference. Therefore, an idealized relationship is V_OUT ≈ 2.5 × (1 + R1/R2).

This equation is only the starting point. In an actual design, reference tolerance, amplifier offset, resistor tolerance, temperature drift, loop compensation and loading must be included in the accuracy and stability analysis.

Applications

· SMPS and DC-DC converter feedback

· AC-DC adapter regulation

· Battery charger feedback and monitoring

· Power-supply management

· Over-voltage and under-voltage detection

· Analog signal conditioning

· Data-acquisition systems

· Threshold detection and monitoring

· Low-frequency analog control loops

· Industrial embedded power electronics

TSM103 vs TSM103W

The original TSM103/A datasheet is marked “NOT FOR NEW DESIGN – REPLACED BY TSM103W.” The TSM103W is the active STMicroelectronics family and retains the dual-op-amp plus 2.5 V-reference architecture. Current listed versions include SO-8 industrial parts such as TSM103WID, TSM103WIDT, TSM103WAID and TSM103WAIDT.

Feature	TSM103/A	TSM103W
Status	Not for new design	Active
Reference	2.5 V	2.5 V
Reference precision	0.4% and 1% variants	±0.4% or ±0.7%
Package examples	SO-8; legacy documentation also exists	SO-8
Recommended for new design	No	Yes, subject to application review

Design Considerations

· Use the active TSM103W family for new designs unless a legacy design specifically requires TSM103/A.

· Keep feedback and sensing traces short and away from high dv/dt switching nodes.

· Use appropriate resistor tolerances when output-voltage accuracy matters.

· Account for the amplifier output swing limitation near the positive rail.

· Check the reference loading and specified sink-current range.

· Analyze loop stability when the device is part of an SMPS feedback loop.

· Provide appropriate local supply bypassing close to the IC.

· Check the exact datasheet for the selected ordering code and temperature grade before production release.

Advantages

· Integrated 2.5 V reference and two amplifier functions

· Reduced external component count

· Reduced PCB area

· Useful for power-supply feedback

· Low input offset voltage

· Low supply current

· Wide supply-voltage range

· Suitable for analog monitoring and control

Limitations

· The legacy TSM103/A is not recommended for new designs.

· The op-amp output does not swing completely to the positive supply rail.

· The reference and amplifier characteristics have to be considered together in precision applications.

· The device is not a complete SMPS controller; it normally works with an external PWM/control stage.

Conclusion

The TSM103 is a useful analog building block for power electronics and embedded systems because it combines a dual operational amplifier with a fixed 2.5 V voltage reference. Its low offset voltage, low supply current, wide supply range and integrated reference make the architecture well suited to power-supply feedback, monitoring, battery charging and data-acquisition applications.

For new products, the active TSM103W should be evaluated because STMicroelectronics lists the original TSM103/A as not for new design. Selecting the correct accuracy grade, package, temperature range and feedback configuration is important for a reliable production design.

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