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TPS40132RHBT Datasheet(PDF) 11 Page - Texas Instruments |
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TPS40132RHBT Datasheet(HTML) 11 Page - Texas Instruments |
11 / 40 page www.ti.com Current Sensing and Balancing (U1, U9 and U18) Hiccup Mode PowerGood Soft-Start SS SS 6 0.6 C t 5 10- ´ » ´ (1) Overcurrent Protection IL IM P H(m a x) C S V 3 .7 5 I R = ´ ´ (2) I PH(max) + I OUT 2 ) V IN * VOUT V OUT 2 L OUT f SW V IN (3) TPS40132 SLUS776A – DECEMBER 2007 – REVISED FEBRUARY 2008 The controller employs peak current mode control scheme, thus naturally provides certain degree of current balancing. With current mode, the level of current feedback should comply with certain guidelines depending on duty factor known as “slope compensation” to avoid the sub-harmonic instability. This requirement can prohibit achieving a higher degree of phase current balance. To avoid the controversy, a separate current loop that forces phase currents to match is added to the proprietary control scheme. This effectively provides high degree of current sharing independent of the controller’s small signal response and is implemented in U9, ICTLR. The useable range of the controller bandwidth is also extended. High bandwidth current amplifiers, U1 and U18 can accept as an input voltage either the voltage drop across dedicated precise current sense resistors, or inductor’s DCR voltage derived by an RC network. The wide range of current sense arrangements ease the cost/complexity constraints and provides superior performance compared to controllers utilizing the low-side MOSFET current sensing. See the Inductor DCR Current Sense section for more information on selecting component values for the R-C network. When the soft-start cycle is complete and soft-start voltage exceeds 1 V, the hiccup mode is enabled for output overcurrent and undervoltage protection. The hiccup mode is invoked when overcurrent or undervoltage faults are detected. the hiccup mode allows a time for a fault to clear itself, for instance, a momentary short circuit on the output. The hiccup mode consists of 7 cycles of charging and discharging the soft-start capacitor, and then attempting a re-start. If the fault has been cleared, the re-start causes the output to come up in regulation. If the fault has not been cleared, the hiccup mode is initiated again, and another restart occurs after another 7 soft-start cycles. The PGOOD pin indicates when the inputs and output are within their specified ranges of operation. Also monitored are the EN/SYNC and SS pins. PGOOD has high impedance when indicating inputs and outputs are within specified limits and is pulled low to indicate an out-of-limits condition. . A capacitor connected to the soft start pin (SS) sets the power-up time. When EN is high and POR is cleared, the calibrated current source starts charging the external soft start capacitor. The PGOOD pin is held low during the start up. The rising voltage across the capacitor serves as a reference for the error amplifier, U12. When the soft-start voltage reaches the level of the reference voltage, the converter’s output reaches the regulation point and further voltage rise of the soft start voltage has no effect on the output. When the soft start voltage reaches 1.0 V, the power good (PGOOD) function is cleared to be reported on the PGOOD pin. Normally the PGOOD pin goes high at this time. Equation 1 is used to calculate the value of the soft-start capacitor. The overcurrent function, U19, monitors the output of current sense amplifiers U1 and U18. These currents are converted to voltages and compared to the voltage on the ILIM pin. The relationship between the maximum phase current and the current sense resistance is given in the following equation. In case a threshold of VILIM/3.75 is exceeded the PWM cycle on the associated phase is terminated. The overcurrent threshold, IPH(max), and the voltage to set on the ILIM pin is determined by Equation 2 and Equation 3. where • I PH(max) is a maximum value of the phase current allowed • I OUT is the total maximum DC output current Copyright © 2007–2008, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s) :TPS40132 |
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