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Integrated Analog Temperature Sensor for High Current Lowside Switches

IP.com Disclosure Number: IPCOM000129023D
Published in the IP.com Journal: Volume 5 Issue 10A (2005-10-25)
Included in the Prior Art Database: 2005-Oct-25
Document File: 3 page(s) / 61K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

A high peak power during short circuits is dangerous especially for high current devices. Thus, a temperature protection/sensing is necessary for high current switch devices (for example a Power-MOS, Metal-Oxide Semiconductor) to protect them against overload and/or short circuits of the load resistance. Classical solutions of over-temperature protection for a Power-MOS are: - to have a sensor on the attached topchip. But sometimes the thermal coupling is not strong enough to sense any occurrence of over-temperature with sufficient speed and accuracy. - to use the leakage current. This fails because of the very low “electrical headroom” (electrical headroom means the potential difference between drain and source) in case of overload on the chip. Furthermore a temperature prewarning is not possible. - to use an isolated temperature sensor (for example a poly-diode). But this usually needs additional process steps. In the following a further concept of temperature protection for high current devices is proposed. This proposal is based on the use of the parasitic NPN-Transistor of a Power-MOS and provides a solution for monolithic Power-MOS switch protection in lowside configuration (see Figure 1 and 2). Also a temperature monitoring (as a prewarning feature) is possible.

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Integrated Analog Temperature Sensor for High Current Lowside Switches

Idea: Fabrizio Cortigiani, IT-Padova; Michael Lenz, DE-Munich

A high peak power during short circuits is dangerous especially for high current devices. Thus, a temperature protection/sensing is necessary for high current switch devices (for example a Power- MOS, Metal-Oxide Semiconductor) to protect them against overload and/or short circuits of the load resistance.

Classical solutions of over-temperature protection for a Power-MOS are:

- to have a sensor on the attached topchip. But sometimes the thermal coupling is not strong enough to sense any occurrence of over-temperature with sufficient speed and accuracy.

- to use the leakage current. This fails because of the very low "electrical headroom"

(electrical headroom means the potential difference between drain and source) in case of overload on the chip. Furthermore a temperature prewarning is not possible.

- to use an isolated temperature sensor (for example a poly-diode). But this usually needs additional process steps.

In the following a further concept of temperature protection for high current devices is proposed. This proposal is based on the use of the parasitic NPN-Transistor of a Power-MOS and provides a solution for monolithic Power-MOS switch protection in lowside configuration (see Figure 1 and 2). Also a temperature monitoring (as a prewarning feature) is possible.

In Figure 1 the parasitic NPN-Transistor (source=E, body=base, drain=C) of a Power-MOS is used as a temperature sensor. The base of the parasitic NPN-Transistor is voltage driven (by a constant voltage) and the emitter is loaded by a constant current or a current with a special temperature coefficient. The control unit (control chip) observes the voltage between base and emitter and compares this with a reference (a constant or a Positive Temperature Coefficient PTC). When the Power-MOS junction is heated up to a certain switch-off temperature, the control unit provides an over thermal shutdown (OTSD) signal/flag.

In case of low voltage at the drain (low ohmic switch on and medium loaded) the parasitic PNP is activated and will be fed from the constant voltage source. This current will not have a big influence on the accuracy of the measurement because only the Vbe is measured by a delta-Voltage detector.

With a second stage comparator additionally a temperature prewarning feature is possible. When the temperature rises above a certain threshold, an over-temperature prewarning flag is set. This threshold is different to the one that is used for OTSD. In the following this threshold is called over thermal prewarning (OTPW). If the device is heated up further, then the over-temperature protection switches off the device and sets an over-...