Datenblatt-Suchmaschine für elektronische Bauteile |
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LM34927SD Datenblatt(PDF) 11 Page - Texas Instruments |
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LM34927SD Datenblatt(HTML) 11 Page - Texas Instruments |
11 / 26 page + VIN UVLO VIN RUV1 CIN RUV2 2 3 LM34927 LM34927 www.ti.com SNVS799F – APRIL 2012 – REVISED DECEMBER 2013 Under Voltage Detector The LM34927 contains a dual level Undervoltage Lockout (UVLO) circuit. When the UVLO pin voltage is below 0.66 V, the controller is in a low current shutdown mode. When the UVLO pin voltage is greater than 0.66 V but less than 1.225 V, the controller is in standby mode. In standby mode the VCC bias regulator is active while the regulator output is disabled. When the VCC pin exceeds the VCC undervoltage thresholds and the UVLO pin voltage is greater than 1.225V, normal operation begins. An external set-point voltage divider from VIN to GND can be used to set the minimum operating voltage of the regulator. UVLO hysteresis is accomplished with an internal 20 μA current source that is switched on or off into the impedance of the set-point divider. When the UVLO threshold is exceeded, the current source is activated to quickly raise the voltage at the UVLO pin. The hysteresis is equal to the value of this current times the resistance RUV2. Table 2. Under Voltage Detector UVLO VCC Mode Description <0.66 V Shutdown VCC regulator disabled. Switcher disabled. 0.66 V-1.225 V Standby VCC regulator enabled. Switcher disabled. >1.225 V VCC < 4.5 V Standby VCC regulator enabled. Switcher disabled. VCC > 4.5 V Operating VCC enabled. Switcher enabled. If the UVLO pin is wired directly to the VIN pin, the regulator will begin operation once the VCC undervoltage is satisfied. Figure 15. UVLO Resistor Setting Thermal Protection The LM34927 should be operated so the junction temperature does not exceed 150°C during normal operation. An internal Thermal Shutdown circuit is provided to protect the LM34927 in the event of a higher than normal junction temperature. When activated, typically at 165°C, the controller is forced into a low power reset state, disabling the buck switch and the VCC regulator. This feature prevents catastrophic failures from accidental device overheating. When the junction temperature reduces below 145°C (typical hysteresis = 20°C), the VCC regulator is enabled, and normal operation is resumed. Copyright © 2012–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM34927 |
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