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LTC2974 数据表(PDF) 54 Page - Linear Technology |
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LTC2974 数据表(HTML) 54 Page - Linear Technology |
54 / 108 page LTC3882-1 54 Rev A For more information www.analog.com APPLICATIONS INFORMATION output filter capacitance for some allowed output voltage variation over the anticipated load range. An example of AVP is shown in Figure 37. Refer to LTC Design Solution 10 for additional examples of using AVP to advantage. MFR_VOUT_AVP specifies the percent reduction in pro- grammed VOUT from no load at an output current value equal to IOUT_WARN_LIMIT. LTC3882-1 AVP supports a maximum reduction in VOUT of 15%, corresponding to a ±7.5% tolerance about a nominal output voltage at roughly 50% load. In order to effectively use AVP, apply the following steps. 1. Set IOUT_OC_WARN_LIMIT. This specifies the master phase output current at which the programmed AVP level will apply. Generally this is above the 100% load point to avoid spurious warnings at full load. 2. VOUT_COMMANDshouldbesettothevalueofVOUTde- siredwithnoloadontheoutput.VOUT_MARGIN_HIGH/ LOW also specify no-load values when AVP is enabled. AVP on the LTC3882-1 can only reduce the output from these levels. downstream rails. Due to this, cascade sequencing should not be implemented without an external fast supervisor to monitor downstream rails and assert a system fault if problems occur. Using Output Voltage Servo For best output voltage accuracy, enable digital servo mode on the master phase by setting bit 6 of MFR_PWM_MODE_LTC3882-1. In digital servo mode, the LTC3882-1 will adjust the regulated output voltage based on its related ADC voltage reading. Every 90ms the digital servo loop will step the LSB of the DAC (nominally 1.375mV or 0.6875mV depending on the voltage range bit) until the output is at the correct ADC reading. When the master channel is turned on, digital servo is enabled after all of the following conditions are satisfied. • MFR_PWM_MODE_LTC3882-1 Bit 6 Is Set • The TON_RISE Sequence Is Complete • A VOUT_UV_FAULT Is Not Present • An IOUT_OC_FAULT Is Not Present • MFR_AVP = 0% Digital servo mode then engages after TON_MAX_ FAULT_LIMIT has expired as shown in Figure 29, unless that limit is set to 0s (infinite). In that case, the mode is engaged as soon as the above conditions are satisfied. Using AVP The LTC3882-1 features digitally programmable active voltage positioning (AVP), where output voltage set point is automatically adjusted as a function of output current at the full bandwidth of the converter. AVP normally entails specifyinganoutputloadlineforavoltagemodeswitcherto allowcurrentsharingbetweenmasterphasesconnectedin parallel. While AVP can be used to this effect in LTC3882-1 applications, use of the LTC3882-1 IAVG current sharing control loop is recommended instead. This will produce more accurate sharing across a wider number of phases without degrading supply output impedance. However,AVPcanstillbeusedtogreatbenefitinLTC3882-1 applications. AVP can be applied to minimize the size of Figure 37. Active Voltage Positioning 38821 F37 WITH AVP AVP DISABLED IO (10A/DIV) VOUT (50mV/DIV) IO (10A/DIV) LOOP: BW = 118kHz, PM = 58°, GM = 7dB VOUT (50mV/DIV) 108mV 173mV |
类似零件编号 - LTC2974 |
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