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TPS51315RGFR датащи(PDF) 10 Page - Texas Instruments |
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TPS51315RGFR датащи(HTML) 10 Page - Texas Instruments |
10 / 28 page PWM Frequency and Adaptive On Time Control ( ) 12 OUT ON T on IN (2 / 3)V 100mV T 19 10 R 50ns V - æ ö + = ´ ´ + ç ÷ è ø (3) Soft-Start Powergood Output Discharge Control TPS51315 SLUS881 – MAY 2009........................................................................................................................................................................................................ www.ti.com TPS51315 employs an adaptive on-time control scheme and does not include a dedicated oscillator on the device. However, the device runs with pseudo-constant frequency by feed-forwarding the input voltage and output voltage to the on-time, one-shot timer. The on-time control is inversely proportional to the input voltage and proportional to the output voltage, so that the duty ratio is maintained as VOUT/VIN with the same cycle time, as shown in Equation 3. where • R T(on)x is the external resistor connected from TON to LL For the TPS51315, the input voltage is monitored at the LL pin during the ON state. An advantage of switching-node monitoring is that any loss in the high-side n-channel FET becomes part of the on-time calculation, thereby making the frequency more stable with load. Another consideration regarding frequency is jitter. Jitter may have many causes, but the constant on-time D-CAP mode scheme has some amount of inherent jitter. Because the output voltage ripple height is in the range of approximately 20 mV, on the order of a milli-volt of noise on the feedback signal can affect the frequency between approximately 3% and 10%. This is normal operation and risks only a small amount of influence to the power supply performance. The TPS51315 includes an independent, internal, 1.06-ms, voltage servo soft-start function with overcurrent limit. When the EN_PSV pin goes high, an internal digita-to-analog converter (DAC) begins ramping up the reference voltage to the error amplifier. Smooth control of the output voltage is maintained during start-up. The TPS51315 includes a powergood output function. The powergood function is activated after the soft-start function has completed. If the output voltage comes within ±5% of the target value, internal comparators detect a powergood state and the powergood signal becomes high after a 64- µs internal delay. If the output voltage rises above or falls below 10% of the target value, the powergood signal goes low immediately. The TPS51315 discharges output when EN_PSV is low or when the channel is in either a UVP or OVP fault condition. The TPS51315 discharges output using an internal 20- Ω MOSFET that is connected to VOUT_DS and PGND. The current capability of the MOSFET is limited to discharge slowly. An external resistor can be connected between VOUT_DS and VOUT to program discharge slow rate. In case the discharge function is not wanted, leave VOUT_DS open. 10 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated Product Folder Link(s): TPS51315 |
Аналогичный номер детали - TPS51315RGFR |
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Аналогичное описание - TPS51315RGFR |
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