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TP2150B Folha de dados(PDF) 11 Page - Tripath Technology Inc. |
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TP2150B Folha de dados(HTML) 11 Page - Tripath Technology Inc. |
11 / 18 page Tr i p ath Technol ogy, I n c. - Techni cal In fo rma t io n 11 TP2150B - MC/ 1.7/06.04 Application Information Overcurrent Protection The TP2150B has over-current protection circuitry to protect itself and the output MOSFETs from short-circuit conditions. The TP2150B uses the voltage across a resistor RS (measured via OCS1HP, OCS1HN, OCS1LP and OCS1LN for channel 1 of the TP2150B) that is in series with each output MOSFET to detect an over-current condition. RS and ROCR are used to set the over- current threshold. The OCS pins must be Kelvin connected for proper operation. The TP2150B has overcurrent sense pins for both the high side output MOSFETs and the low side output MOSFETs. The OCSXHP and OCSXHN pins (pins 33 and 34, pins 50 and 51) sense the amount of current flowing out of the high side MOSFET. The OCSXLP and OCSXLN pins (pins 30 and 31, pins 53 and 54) sense the amount of current flowing into the low side MOSFET. These pins sense the voltage across a low resistance value resistor (RS) and this voltage is gained up and reflected at OCD1 (pin7) for channel 1. The OCD pins can be used to trigger an overcurrent condition at the output MOSFETs and then turn off the processor. Setting Over-current Threshold RS and ROCR determine the value of the over-current threshold, ISC: ISC = 3580 x (VTOC – IBIAS * ROCR)/(R OCR * RS) ROCR = (3580 x VTOC)/(ISC * RS+3580 * IBIAS) where: RS and ROCR are in Ω VTOC = Over-current sense threshold voltage for the processor = 1.0V (typically for the Tripath TC2000 and TC2001) IBIAS = 20uA For example, to set an ISC of 4.73A, ROCR = 30.1kΩ and RS will be 10mΩ. As high-wattage resistors are usually only available in a few low-resistance values (10m Ω, 25mΩ and 50m Ω), ROCR can be used to adjust for a particular over-current threshold using one of these values for RS. It should be noted that the addition of the bulk CHBR capacitor shown in the Application / Test Diagram will increase the ISC level. Thus, it will be larger than the theoretical value shown above. With CHBR as shown in the typical application circuit, and with ROCR = 30.1kΩ and RS 10mΩ, the typical current trip point is 7A. Once the designer has settled on a layout and specific CHBR value, the system ISC trip point can be adjusted by increasing the ROCR value. The ROCR should be increased to a level that allows expected range of loads to be driven well into clipping without current limiting while still protecting the output MOSFETs in case of a short circuit condition. VN10 Supply and Switch Mode Power Supply Controller VN10 is an additional supply voltage required by the TP2150B. VN10 must be 10 volts more positive than the nominal VNN. VN10 must track VNN. Generating the VN10 supply requires some care. The proper way to generate the voltage for VN10 is to use a 10V-postive supply voltage referenced to the VNN supply. The TP2150B has an internal switch mode power supply controller which generates the necessary floating power supply for the MOSFET driver stage in the TP2150B (nominally 10V with the external components shown in Application / Test Circuit). The SMPSO pin (pin 60) provides a switching output waveform to drive the gate of a P channel MOSFET. The source of the P channel MOSFET should be tied to power ground and the drain of the MOSFET should be tied to the VN10 through a 100uH inductor. Tripath recommends using |
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Descrição semelhante - TP2150B |
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