Difference Between Series and Shunt Voltage Reference ICs
Voltage reference ICs provide a stable, precise voltage that does not vary with supply voltage, temperature, or load current. Based on how they are connected and how regulation is achieved, voltage references are broadly classified into:
- Series Voltage Reference ICs
- Shunt Voltage Reference ICs
Understanding the difference is crucial when designing ADC reference circuits, calibration equipment, power supplies, and precision instrumentation.
1️⃣ What is a Series Voltage Reference?
Basic Concept
A series reference is connected in series with the load, similar to a linear voltage regulator.
It sources current to the load while maintaining a fixed output voltage.
Connection Style
VIN ──► Series Reference IC ──► VREF ──► Load ──► GND
How It Works
- Internally, the IC contains:
- A precision reference core (bandgap or buried zener)
- An error amplifier
- A pass transistor
- The IC continuously adjusts the pass element to maintain a constant output voltage at VREF.
✅ Key Characteristics of Series References
| Feature | Description |
| Output current | Sources current to the load |
| External components | Very few |
| Noise | Low |
| Accuracy | High |
| Efficiency | Lower (drops voltage across IC) |
| Stability | Very good |
Example: AD584 / REF102 / ADR4540
Example Circuit (AD584 – 10V output):
15V Supply
│
├── AD584 ──► 10V Reference ──► ADC / DAC
│
GND
- The AD584 internally regulates and provides 10V directly to the load.
- Load current is drawn from the IC, not from an external resistor.
Typical Applications of Series References
- ADC/DAC reference voltage
- Precision instrumentation
- Calibration equipment
- Industrial control systems
- High-resolution data acquisition
2️⃣ What is a Shunt Voltage Reference?
Basic Concept
A shunt reference works like a precision zener diode.
It is connected in parallel with the load and sinks current to maintain a constant voltage.
Connection Style
VIN ──► R ──► VREF ──► Load
│
└── Shunt Reference ──► GND
How It Works
- A resistor limits current from the supply.
- The shunt reference draws (sinks) extra current to maintain VREF.
- If load current changes, the shunt current adjusts accordingly.
✅ Key Characteristics of Shunt References
| Feature | Description |
| Output current | Sinks current only |
| External components | Requires resistor |
| Noise | Higher than series |
| Accuracy | Moderate to high |
| Efficiency | Lower at high currents |
| Stability | Good (but resistor dependent) |
Example: LM4040 / TL431
Example Circuit (LM4040 – 2.5V):
5V
│
├─ 1kΩ ──► 2.5V ──► MCU ADC
│ │
│ LM4040
│ │
└────────── GND
- The resistor supplies current.
- LM4040 clamps the voltage at 2.5V.
- Excess current is shunted to ground.
Typical Applications of Shunt References
- MCU ADC reference pins
- Low-cost embedded systems
- Overvoltage clamps
- Simple precision references
- Battery-powered devices (low current)
3️⃣ Key Differences: Series vs Shunt Reference
| Parameter | Series Reference | Shunt Reference |
| Connection | In series with load | In parallel with load |
| Current behavior | Sources current | Sinks current |
| External resistor | Not required | Required |
| Noise | Low | Higher |
| Accuracy | High | Medium–High |
| Power efficiency | Better at high load | Poor at high load |
| Load regulation | Excellent | Good |
| Complexity | Moderate | Very simple |
| Cost | Higher | Lower |
4️⃣ Which One Should You Use?
✅ Use a Series Reference when:
- You need high accuracy & low noise
- Driving ADC/DAC reference pins
- Load current varies
- Precision is critical
Example:
16-bit ADC reference → ADR4540
✅ Use a Shunt Reference when:
- Circuit simplicity is important
- Load current is small and stable
- Cost-sensitive design
- Supply voltage is fixed
Example:
MCU ADC reference → LM4040
5️⃣ Real-World Design Comparison
ADC Reference Example
| ADC Type | Recommended Reference |
| 10-bit MCU ADC | LM4040 |
| 12-bit ADC | LM4040 / REF30 |
| 16-bit ADC | AD584 |
| 24-bit ADC | ADR4540 |
6️⃣ Quick Summary
- Series references regulate voltage actively and supply current directly.
- Shunt references regulate by sinking excess current.
- Series references offer better performance, while shunt references offer simplicity and low cost.
- Selection depends on precision, current, noise, cost, and supply constraints.
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