Industrial Sensors (12V / 24V power supply)

Industrial sensors are typically powered by the host machine, so the input voltage is often 12V, 24V or more.
They normally include various sensors, an MCU and a means of communication (either wired or wireless). Solutions with small physical size and high reliability are required and applications include building automation and security, monitoring of machinery, robotics etc.

Although the number of applications is large, the typical circuit configuration is often similar and designers value efficiency, low output noise, low EMI and small size.

* See "IoT Devices" for solutions to battery-powered industrial sensor.

Block diagram Requirements Recommended ICs Features
Primary Step-down: 12V or 24V to secondary rails

Specifications
VIN: ~18V
VOUT: 3.3 or 5V
IOUT: 500mA

Other points

  • Small size, high power dissipation
  • Keep VOUT even if VIN < VOUT
XCL225 / XCL226 (XC9263 / XC9264)

Inductor built-in step-down DC/DC, PWM (XCL225), PWM/PFM (XCL226)

  • Space saving, high efficiency and high power dissipation with integrated coil
  • Achieves 100% duty ratio with Pch SW to support lower input Voltages
  • If the coil is external, there are also XC9263 (PWM) and XC9264 (PWM / PFM) where the oscillation frequency (fosc) can be selected from 500k,1.2M and 2.2MHz

VIN: 3V~18V
VOUT: 1V~15V (Set by external resistors)
IOUT: 500mA
fosc: 1.2MHz
Maximum Duty ratio: 100% (Pch SW)
Adjustable Soft-start
Power Good function

Specifications
VIN: ~36V
VOUT: 3.3 or 5V
IOUT: 500mA

Other points

  • Small size, high power dissipation
  • Keep VOUT even if VIN < VOUT
XCL230 / XCL231 (XC9267 / XC9268)

Inductor built-in step-down DC/DC, PWM (XCL230), PWM/PFM (XCL231)

  • Space saving, high efficiency and high power dissipation with integrated coil
  • Achieves 100% duty ratio with Pch SW to support lower input Voltages
  • If the coil is external, there are also XC9267 (PWM) and XC9268 (PWM / PFM) where the oscillation frequency (fosc) can be selected from 1.2M and 2.2MHz

VIN: 3~36V (Absolute maximum: 46V at ≦400ms)
VOUT: 1V~5V (Set by external resistors)
IOUT: 600mA
fosc: 1.2MHz
Maximum Duty ratio: 100% (Pch SW)
Adjustable Soft-start
Power Good function

Step-down
For MCU

Specifications
VOUT: 3.0V
IOUT: 100mA

Other points

  • High efficiency
  • Low noise
XCL222

Inductor built-in step-down DC/DC HiSAT-COT PWM/PFM

  • Ideal for avoiding any interference to RF / sensors by low ripple and coil integration
  • High-speed transient response with HiSAT-COT control

VIN: 2.5~5.5V
VOUT: 0.8V~3.6V
IOUT: 500mA
fosc: 1.2MHz

XC9258 (XC9282)

Ultra-small HiSAT-COT step-down DC/DC, PWM/PFM

  • High-speed transient response with HiSAT-COT control
  • 1.2MHz good for efficiency at light load and 6MHz good for transient response and rippe
  • SOT-25 package is ready, ideal for industrial equipments where there are restrictions on packages without lead terminals

VIN: 2.5V~5.5V
VOUT: 0.8V~3.6V
IOUT: 1A
fosc: 1.2MHz, 6.0MHz

Step-down / LDO
For Sensor

Specifications
VOUT: 3.0V
IOUT: 100mA

Other points

  • Turn ON/OFF by MCU
  • Low noise
XC9281 / XC9282

Ultra small HiSAT-COT step-down DC/DC, PWM(XC9281), PWM/PFM(XC9282)

  • World's smallest solution (3.52mm2)
  • High-speed transient response
  • High fosc and low ripple, ideal for RF / sensors

VIN: 2.5V~5.5V
VOUT: 1.2V~3.6V
IOUT: 600mA
fosc: 4.0MHz, 6.0MHz

XCL221 / XCL222

Inductor built-in HiSAT-COT Step-down DC/DC, PWM (XCL221), PWM/PFM (XCL222)

  • Ideal for avoiding any interference to RF / sensors by low ripple and coil integration
  • High-speed transient response with HiSAT-COT control

VIN: 2.5V~5.5V
VOUT: 0.8V~3.6V
IOUT: 500mA
fosc: 1.2MHz

XC6233 / XC6223XC6215

Fast transient response / high PSRR voltage regulator

  • Low noise ideal for sensor
  • Low consumption regulator: XC6215 may be suitable for applications where noise above 100kHz is important

VIN: 1.7V~5.5V
VOUT: 1.2V~3.6V
IOUT: 200mA (XC6223: 300mA)

RESET
To monitor 12V / 24V input

Specifications
Detect voltage: 6.0V

Other points

  • 5% or higher hysteresis (Any of the detection / release voltage)
  • Release delay: 20ms
XC6118XC6134

Low consumption voltage detector with separated sense pin and delay function by a capacitor

  • Ideal for 12V / 24V input monitor with dividing resistors with separate sense pin
  • Startup sequence is configured with a release delay by an external capacitor
  • Any detection / release voltage can be set with the hysteresis external adjustment function for stable operation of the equipment

VIN: 1.1V~6.0V
Detect voltage: 0.8V~5.0V (Sense pin separated, internally fixed)
Iq: 0.4μA

Solution Summary

Primary step-down DC/DC

Industrial equipment will often be powered from a 12V or 24V primary power rail. Typical applications include, industrial sensors, factory automation and control equipment and robotics. Increasingly these application demand ever smaller, lower power solutions where efficiency and power dissipation become critically important.

Block diagram (a) shows an example circuit where the primary DC/DC is directly powering the MCU.
If the system spends periods of time in a low power mode, a DC/DC which switches automatically between PWM and PFM should be selected to maximise the efficiency under different load conditions. Alternatively a DC/DC with fixed PWM mode can be used if a constant frequency is preferred or if the output load is always at a higher level.
If the input Voltage is likely to drop to levels at or below the output Voltage, then a DC/DC with internal Pch switch, capable of operating with 100% duty cycle, should be used in order to maintain the output Voltage for as long as possible under adverse conditions.

Step-down DC/DCs, 18V operation
XCL225: Inductor built-in type PWM
XCL226: Inductor built-in type PWM/PFM
XC9263: PWM
XC9264: PWM/PFM
Step-down DC/DCs, 36V operation (46V rating ≦ 400ms)
XCL230: Inductor built-in type PWM
XCL231: Inductor built-in type PWM/PFM
XC9267: PWM
XC9268: PWM/PFM

Sometimes, large capacitors are placed at the output of a primary DC/DC to help reduce output ripple and suppress fluctuations if a load with large peak current is drawn quickly.
In such cases, the normal start-up sequence can sometimes fail due to excessive inrush currents which may trigger the DC/DCs protection circuits.
To overcome this issue, it can be necessary to adjust the start-up sequence by delaying the DC/DC's soft-start time or to monitor by using the DC/DC's Power Good output signal.

LDO and DC/DC for sensor

In our example, the Voltage rail required to drive the sensor is close to the system Voltage so a LDO Voltage Regulator can be used efficiently.

As a general rule, if Voltage Regulator is used, a high speed LDO Regulator, with high Power Supply Ripple Rejection (PSRR) and fast load transient response should be chosen to ensure a clean supply.
However, if the output noise at higher frequencies (>100kHz) is an important consideration, then a low power LDO with lower IQ may be more suitable because their output noise can be surprisingly low at high frequencies.

Voltage regulators
XC6233: High speed, 200mA
XC6223: High speed, 300mA
XC6215: Low power

If the Voltage difference between the primary and secondary rails for the MCU and Sensors is large or if the devices being supplied require higher load currents, a DC/DC converter will normally be preferred over an LDO Voltage Regulator. We illustrate this circuit configuration in block diagram (b).

Step-down DC/DC for MCU from primary DC/DC (Block diagram (b))

In a system where there are two distinct Voltage levels, we often refer to the initial power stage as the 'Primary' and the the next stage as the 'Secondary'. For example the 'primary' stage in our digram is the initial step-down from DC to 5.0V. The 'Secondary' stage includes all the subsequent rails powered from 5.0V, so in our example the two 3.3V rails are both 'Secondary'.

The primary side is the same as Block diagram (a) above. However for the secondary stage, it is possible to use lower Voltage DC/DC which are often smaller and more compact. Designers often prefer PWM/PFM auto switching DC/DC to maintain higher efficiencies at lower loads.

Step-down DC/DCs
XCL222: Inductor built-in type PWM/PFM, 1.2MHz / high efficiency / low EMI
XC9258: PWM/PFM, high-speed transient response, 6MHz type is particularly well-suited to applications where transient response is important. Also available in SOT25 package for easy soldering.
XC9282: PWM/PFM, world's smallest solution (3.52mm2), low EMI

DC/DC with fixed PWM mode are also available if a constant frequency is preferred or if the output load is always at a higher level.

Fixed PWM types for the above, respectively
XCL221, XC9257, XC9282

Voltage Detector for input voltage monitoring

In our example we use a Voltage Detector with seperated VSEN pin to monitor the primary side input Voltage.
Monitoring the input Voltage to helps to ensure stable operation and is useful for power sequencing (when implementing a start-up and shut-down routine).

The VSEN pin uses divider resistors which are connected to the primary side input Voltage supply. The divider circuit allows the Voltage Detector to monitor Voltages that exceed the absolute maximum Voltage range of the IC. The VIN supply for the Voltage Detector is connected to the output side of the primary DC/DC (5.0V in our example circuit).

Below we explain the operation of the Voltage Detector block:
Let us assume the following: VIN=12.0V, Primary DC/DC VOUT=5.0V, Voltage Detector: Detection Voltage=8.0V, Release Voltage=8.4V (8.0V + 5% hysterisis)

During input Voltage application

When DC 12V rises up and the primary DC/DC output Voltage reaches 5V, PG becomes 'H'.
This causes the secondary stage CE to go 'H' and the secondary DC/DC starts-up and supplies voltage to the MCU and sensor.
If the Voltage Detector input voltage exceeds the release voltage of 8.4V, RESETB becomes 'H' and the MCU is notified that the input voltage is normal.
The Voltage Detector is not monitoring the DC/DC output Voltage, so it is necessary to set a release delay time (using the Cd pin capacitor )which takes into account the rise-up time of the DC/DC's output Voltage.

During input Voltage drop or cut-off

If the input Voltage falls below the detect voltage of 8.0V, RESETB becomes 'L' and the MCU is notified of the voltage drop.
In response to this signal, the MCU can decide to safely stop operation before the DC/DC output voltage drops or it may need to execute back-up procedures to save important data before the power fails.

Additional measures

If the primary DC/DC output Voltage drops suddenly, the PG signal will be go 'L' and this will turn off the secondary DC/DC via it's CE pin. If this happens quickly, the MCU may not have enough time to implement its safe shut-down or back-up routines.
To protect against this, it may be necessary to increase the primary DC/DC output capacitance and implement a CR circuit to delay the CE of the secondary DC/DC. This will prevent the CE going 'L' too quickly.
By adding a another Voltage Detector to the Secondary DC/DC output line it is possible to configure a circuit to ensure the MCU cannot be activated before the power is supplied to the MCU. In this case, the release delay of the voltage detector that monitors the primary side is not necessary.

With some Voltage Detectors the Release Voltage Hysteresis can also be adjusted externally as well as the Detection delay time

HYS (Hysteresis) external adjustment

In our example above, the detect and release voltages were 8.0V and 8.4V (HYS=5%). But with adjustable hysteresis it would be possible to set a detection Voltage of 7.0V with a release of 9.5V. This is advantageous because with a 7.0V detection threshold, the circuit will continue working for longer during a Voltage drop. The higher 9.5V release threshold ensures stable operation during rise-up.
With older style Voltage Detectors, such a large hysteresis is not possible (7V/9.5V, HYS=+36%), however the newer generation of Voltage Detectors allow the user to adjust many settings externally with resistors and a wide range of detect and release configurations can be easily realised.
This flexibility is useful for all types of industrial equipment, especially where the power supply line is long and unstable.

Setting of detection delay time

If the voltage drop is only for a very short duration it can be desirable not to stop the MCU, so to avoid false resets a Voltage Detector with the detect delay function can be used.

Voltage detectors
XC6118: Separated Sense pin, release delay with external Cd
XC6134: XC6134: Separated Sense Pin, HYS (hysteresis) external adjustment, release/detection delay with external Cd

As we have seen, small, compact DC/DC and Voltage Detectors can be used to a configure a simple power supply, optimised for safe, efficient operation.
In the past, Voltage Regulators were used more frequently, but with greater emphasis now placed on overall power efficiency and reducing the system power consumption, DC/DC are increasingly becoming the preferred choice for new designs.
The use of configurable Voltage Detectors is also helping to ensure greater system reliability with more accurate control and monitoring of the power circuit operation. These attributes are popular for designers of Industrial equipment and medical devices.

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