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TPS53129PW Datasheet(PDF) 10 Page - Texas Instruments |
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TPS53129PW Datasheet(HTML) 10 Page - Texas Instruments |
10 / 29 page V = TRIP (V-V ) IN O 2 1 · · L f SW ¾ · V O ¾ V IN · RDS(ON) I - OCL ( ) R (k )= TRIP W V (mV) TRIP I ( A) TRIP m ¾ TPS53129 SLVSAE6B – OCTOBER 2009 – REVISED JULY 2010 www.ti.com 5-Volt Regulator The TPS53129 has an internal 5-V low-dropout (LDO) regulator to provide a regulated voltage for all both drivers and the IC's internal logic. A high-quality 4.7-mF or greater ceramic capacitor from VREG5 to GND is required to stabilize the internal regulator. An internal 10- Ω resistor from VREG5 filters the regulator output to the IC's analog and logic input voltage, V5FILT. An additional high-quality 1.0-mF ceramic capacitor is required from V5FILT to GND to filter switching noise from VREG5. Soft Start The TPS53129 has a programmable soft-start . When the ENx pin becomes high, 2.0-mA current begins charging the capacitor connected from the SS pin to GND. The internal reference for the D-CAP2™ mode control comparator is overridden by the soft-start voltage until the soft-start voltage is greater than the internal reference for smooth control of the output voltage during start up. Pre-Bias Support The TPS53129 supports pre-bias start-up without sinking current from the output capacitor. When enabled, the low-side driver is held off until the soft-start commands a voltage higher than the pre-bias level (internal soft-start becomes greater than feedback voltage (VFB)), then the TPS53129 slowly activates synchronous rectification by limiting the first DRVL pulses with a narrow on-time. This limited on-time is then incremented on a cycle-by-cycle basis until it coincides with the full 1-D off-time. This scheme prevents the initial sinking of current from the pre-bias output, and ensure that the output voltage (VOUT) starts and ramps up smoothly into regulation and the control loop is given time to transition from pre-biased start-up to normal mode operation. Output Discharge Control TPS53129 discharges the outputs when ENx is low, or the controller is turned off by the protection functions (OVP, UVP, UVLO, and thermal shutdown). The device discharges output using an internal 40- Ω MOSFET which is connected to VOx and PGNDx. The external low-side MOSFET is not turned on during the output discharge operation to avoid the possibility of causing negative voltage at the output. This discharge ensures that on start the regulated voltage always initializes from 0 V. Over Current Limit TPS53129 has cycle-by-cycle over current limit feature. The over current limits the inductor valley current by monitoring the voltage drop across the low-side MOSFET RDS(ON) during the low-side driver on-time. If the inductor current is larger than the over current limit (OCL), the TPS53129 delays the start of the next switching cycle until the sensed inductor current falls below the OCL current. MOSFET RDS(ON) current sensing is used to provide an accuracy and cost effective solution without external devices. To program the OCL, the TRIP pin should be connected to GND through a trip voltage setting resistor, according to the following equations. (2) (3) The trip voltage should be between 30 mV to 300 mV over all operational temperature, including the 4000-ppm/°C temperature slope compensation for the temperature dependency of the RDS(ON). If the load current exceeds the over current limit, the voltage will begin to drop. If the over current conditions continues the output voltage will fall below the under voltage protection threshold and the TPS53129 will shut down. In an over current condition, the current to the load exceeds the current to the output capacitor; thus the output voltage tends to fall off. Eventually, it will end up with crossing the under voltage protection threshold and shutdown. 10 Submit Documentation Feedback Copyright © 2009–2010, Texas Instruments Incorporated Product Folder Link(s): TPS53129 |
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