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LM5181-Q1 Scheda tecnica(PDF) 12 Page - Texas Instruments |
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LM5181-Q1 Scheda tecnica(HTML) 12 Page - Texas Instruments |
12 / 33 page + VIN VCC 5 A 1.5 V EN/UVLO UVLO Comparator RUV1 RUV2 LM5181 1.45 V : ª º ¬ ¼ : ˜ ª º ¬ ¼ q ª º ¬ ¼ FB TC PS Diode R k 3 R k N TC mV C 12 LM5181-Q1 SNVSBN6 – APRIL 2020 www.ti.com Product Folder Links: LM5181-Q1 Submit Documentation Feedback Copyright © 2020, Texas Instruments Incorporated Feature Description (continued) 8.3.3.1 Diode Thermal Compensation The LM5181-Q1 employs a unique thermal compensation circuit that adjusts the feedback setpoint based on the thermal coefficient of the forward voltage drop of the flyback diode. Even though the output voltage is measured when the secondary current is effectively zero, there is still a non-zero forward voltage drop associated with the flyback diode. Select the thermal compensation resistor using Equation 9. (9) The temperature coefficient of the diode voltage drop may not be explicitly provided in the diode data sheet, so the effective value can be estimated based on the measured output voltage shift overtemperature when the TC resistor is not installed. 8.3.4 Control Loop Error Amplifier The inputs of the error amplifier include a level-shifted version of the FB voltage and an internal 1.21-V reference set by the resistor at RSET. A type-2 internal compensation network stabilizes the converter. In BCM operation when the output voltage is in regulation, an on-time interval is initiated when the secondary current reaches zero. The power MOSFET is subsequently turned off when an amplified version of the peak primary current exceeds the error amplifier output. 8.3.5 Precision Enable The precision EN/UVLO input supports adjustable input undervoltage lockout (UVLO) with hysteresis for application specific power-up and power-down requirements. EN/UVLO connects to a comparator with a 1.5-V reference voltage and 50-mV hysteresis. An external logic signal can be used to drive the EN/UVLO input to toggle the output on and off for system sequencing or protection. The simplest way to enable the LM5181-Q1 is to connect EN/UVLO directly to VIN. This allows the LM5181-Q1 to start up when VIN is within its valid operating range. However, many applications benefit from using a resistor divider RUV1 and RUV2 as shown in Figure 19 to establish a precision UVLO level. Figure 19. Programmable Input Voltage UVLO With Hysteresis Use Equation 10 and Equation 11 to calculate the input UVLO voltages turnon and turnoff voltages, respectively. |
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