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PT6467 Datasheet(PDF) 5 Page - Texas Instruments |
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PT6467 Datasheet(HTML) 5 Page - Texas Instruments |
5 / 12 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com PT6460 & PT6470 Series Output Remote Sense The (+)Sense pin allows the regulator to compensate for limited amounts of ‘IR’ voltage drop in the positive output connection resistance. This is the voltage drop incurred in the PCB trace between Vout (pins 9 & 10) of the regu- lator and the load some distance away. Connecting (+)Sense to the positive load terminal improves the voltage regu- lation at the load, particularly when the load current fluctuates. Although not recommended, leaving (+)Sense disconnected will not damage the regulator or the load circuitry. An internal 10 Ω resistor, connected between the sense pin and the output, keeps the output voltage in regulation. With the sense pin connected, the difference between the voltage measured between Vout and GND at the regulator, and that measured from (+)Sense to GND, is the amount of IR drop being compensated by the regula- tor. This should be limited to 0.3 V maximum. Note: The remote sense feature is not designed to compensate for the forward drop of non-linear or frequency dependent components that may be placed in series with the converter output. Examples include OR-ing diodes, filter inductors, ferrite beads, and fuses. When these components are enclosed by the remote sense connections they are effectively placed inside the regulation control loop, which can adversely affect the stability of the regulator. Pre-Bias Startup In complex digital systems an external voltage can some- times be present at the output of the regulator during power up. For example, this voltage may be backfed through a dual-supply logic component such as an FPGA or ASIC. Another path might be via a clamp diode (to a lower supply voltage) as part of a power-up sequencing implementation. Although the PT6460 (5-V input) and PT6470 (3.3-V input) series of regulators will sink current under steady- state conditions, they will not do so during startup. This feature allows these regulators to start up while an external voltage is simultaneously applied to the output. To facilitate this feature the input voltage must always be greater than or equal to the output voltage throughout the power-up and power-down sequence. Startup includes both the application of a valid input source voltage, or the removal of a ground signal from the Inhibit* control (pin 1) with a valid input source applied. The output of the regulator is also effectively off (tri-state), during the period that the Inhibit* control is held low. Note: If the pre-bias is greater than the nominal regulation voltage, the module will begin sinking current at the end of its soft-start power-up sequence. This could overstress the regulator if the current exceeds its rated output. Over-Current Protection To protect against load faults, these ISRs incorporate output over-current protection. Applying a load that exceeds the over-current threshold (see data sheet speci- fications) will cause the regulated output to shut down. Following shutdown the ISR will periodically attempt to recover by initiating a soft-start power-up. This is often described as a “hiccup” mode of operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is removed. During this period, the average current flowing into the fault is significantly reduced. Once the fault is removed, the converter automatically recovers and returns to normal operation. Operating Features and System Considerations for the PT6460 & PT6470 Regulator Series The PT6460 (5-V input) and the PT6470 (3.3-V input) series of integrated switching regulators (ISRs) provide step-down voltage conversion for output loads of up to 14 A. Power up & Soft-Start Timing Following either the application of a valid input source voltage, or the removal of a ground signal to the Inhihit* control pin (with input power applied), the regulator will initiate a soft-start power up. A soft start slows the rate at which the output voltage rises and introduces a short time delay, td (approximately 2 ms), into the power-up sequence. Figure 1-1 shows the power-up characteristic of a PT6464 (5-V input, 1.8-V output) with a 8.5-A load. Vo (1V/Div) Iin (2A/Div) Vin (2V/Div) HORIZ SCALE: 5ms/Div t d Figure 1-1 |
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