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PTH05010WAZT Datasheet(PDF) 10 Page - Texas Instruments |
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PTH05010WAZT Datasheet(HTML) 10 Page - Texas Instruments |
10 / 16 page Application Notes For technical support and further information visit http://power.ti.com PTH Series of Wide-Output Adjust Power Modules (3.3/5-V Input) Auto-Track™ Function The Auto-Track function is unique to the PTH family, and is available with the all “Point-of-Load Alliance” (POLA) products. Auto-Track was designed to simplify the amount of circuitry required to make the output voltage from each module power up and power down in sequence. The sequencing of two or more supply voltages during power up is a common requirement for complex mixed-signal applications, that use dual-voltage VLSI ICs such as DSPs, micro-processors, and ASICs. How Auto-Track Works Auto-Track works by forcing the module’s output voltage to follow a voltage presented at the Track control pin. This control range is limited to between 0 V and the module’s set-point voltage. Once the track-pin voltage is raised above the set-point voltage, the module’s output remains at its set-point 1. As an example, if the Track pin of a 2.5-V regulator is at 1 V, the regulated output will be 1 V. But if the voltage at the Track pin rises to 3 V, the regulated output will not go higher than 2.5 V. When under track control, the regulated output from the module follows the voltage at its Track pin on a volt- for-volt basis. By connecting the Track pin of a number of these modules together, the output voltages will fol- low a common signal during power-up and power-down. The control signal can be an externally generated master ramp waveform, or the output voltage from another power supply circuit 3. For convenience the Track control incor- porates an internal RC charge circuit. This operates off the module’s input voltage to provide a suitable rising voltage ramp waveform. Typical Application The basic implementation of Auto-Track allows for simultaneous voltage sequencing of a number of Auto- Track compliant modules. Connecting the Track control pins of two or more modules forces the Track control of all modules to follow the same collective RC ramp wave- form, and allows them to be controlled through a single transistor or switch; Q1 in Figure 3-5. To initiate a power-up sequence the Track control must first pulled to ground potential. This should be done at or before input power is applied to the modules, and then held for at least 10 ms thereafter. This brief period gives the modules time to complete their internal soft-start initialization, which enables them to produce an output voltage. Applying a logic-level high signal to the circuit’s On/Off Control turns Q1 on and applies a ground signal to the Track control. After completing their internal soft-start intialization, the output of all modules will remain at zero volts while Q1 is on. 10 ms after a valid input voltage has been applied to all modules, Q1 can be turned off. This allows the track control voltage to automatically rise toward to the modules' input voltage. During this period the output voltage of each module will rise in unison with other modules, to its respective set-point voltage. Figure 3-6 shows the output voltage waveforms from the circuit of Figure 3-5 after the On/Off Control is set from a high to a low-level voltage. The waveforms, Vo1 and Vo2 represent the output voltages from the two power mod- ules, U1 (3.3 V) and U2 (1.8 V) respectively. Vo1 and Vo2 are shown rising together to produce the desired simul- taneous power-up characteristic. The same circuit also provides a power-down sequence. Power down is the reverse of power up, and is accom- plished by lowering the track control voltage back to zero volts. The important constraint is that a valid input voltage must be maintained until the power down is complete. It also requires that Q1 be turned off relatively slowly. This is so that the Track control voltage does not fall faster than Auto-Track's slew rate capability, which is 1 V/ms. The components R1 and C1 in Figure 3-5 limit the rate at which Q1 can pull down the Track control voltage. The values of 100 k-ohm and 0.1 µF correlate to a decay rate of about 0.17 V/ms. The power-down sequence is initiated with a low-to-high transition at the On/Off Control input to the circuit. Figure 3-7 shows the power-down waveforms. As the Track control voltage falls below the nominal set-point voltage of each power module, then its output voltage decays with all the other modules under Auto-Track control. Notes on Use of Auto-Track™ 1.The Track pin voltage must be allowed to rise above the module’s set-point voltage before the module can regulate at its adjusted set-point voltage. 2.The Auto-Track function will track almost any voltage ramp during power up, and is compatible with ramp speeds of up to 1 V/ms. 3. The absolute maximum voltage that may be applied to the Track pin is Vin. 4.The module will not follow a voltage at its Track control input until it has completed its soft-start initialization. This takes about 10 ms from the time that the module has sensed that a valid voltage has been applied its input. During this period, it is recommended that the Track pin be held at ground potential. 5.The module is capable of both sinking and sourcing current when following a voltage at its Track pin. Therefore startup into an output prebias is not supported during Auto-Track control. Note: A pre-bias holdoff is not necessary when all supply voltages rise simultaneously under the control of Auto-Track. 6.The Auto-Track function can be disabled by connecting the Track pin to the input voltage (Vin). With Auto-Track disabled, the output voltage will rise at a quicker and more linear rate after input power is applied. |
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