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LM76002-Q1 Datasheet(PDF) 22 Page - Texas Instruments |
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LM76002-Q1 Datasheet(HTML) 22 Page - Texas Instruments |
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22 / 54 page  22 LM76002-Q1, LM76003-Q1 SNVSAU3 – DECEMBER 2017 www.ti.com Product Folder Links: LM76002-Q1 LM76003-Q1 Submit Documentation Feedback Copyright © 2017, Texas Instruments Incorporated 7.4 Device Functional Modes 7.4.1 Shutdown Mode The EN pin provides electrical on/off control for the LM76002-Q1/LM76003-Q1. When the EN pin voltage is below 0.3 V (typical), both the regulator and the internal LDO have no output voltages, and the device is in shutdown mode. In shutdown mode the quiescent current drops to typically 1.2 µA. The LM76002-Q1/LM76003- Q1 also employs UVLO protection. If VCC voltage is below the UVLO level, the output of the regulator is turned off. 7.4.2 Standby Mode The internal LDO has a lower EN threshold than the regulator. When the EN pin voltage is above below 1.1 V (maximum) and below the precision enable threshold for the output voltage, the internal LDO regulates the VCC voltage at 3.29 V typically. The precision enable circuitry is ON once VCC is above the UVLO. The internal MOSFETs remain in tri-state unless the voltage on EN pin goes above the precision enable threshold. The LM76002-Q1/LM76003-Q1 also employs UVLO protection. If VCC voltage is below the UVLO level, the output of the regulator is turned off. 7.4.3 Active Mode The LM76002-Q1/LM76003-Q1 is in active mode when the EN pin and UVLO high threshold levels are satisfied. The simplest way to enable the operation of the LM76002-Q1/LM76003-Q1 is to connect the EN pin to VIN, which allows self start-up of the LM76002-Q1/LM76003-Q1 when the input voltage is in the operation range: 3.5 V to 60 V. See Enable (EN Pin) and UVLO for details on setting these operating levels. In active mode, depending on the load current, the LM76002-Q1/LM76003-Q1 will be in one of five sub modes: 1. CCM with fixed switching frequency with load between half of IMINPK to full load. 2. DCM when the load current is lower than half of the inductor current ripple. 3. Light load mode where the device uses pulse frequency modulation (PFM) and lowers the switching frequency at load under half of IMINPK to improve efficiency. 4. Foldback mode when switching frequency is reduced to maintain output regulation with supply voltages that cause the minimum tON or tOFF to be exceeded. 5. Forced-pulse-width modulation (FPWM) is similar to CCM with fixed switching frequency, but extends the fixed frequency range of operation from full to no load. 7.4.4 CCM Mode CCM operation is employed in the LM76002-Q1/LM76003-Q1 when the load current is higher than ½ of the peak-to-peak inductor current. If the load current is decreased, the device enters DCM mode. In CCM operation, the frequency of operation is constant and fixed unless the minimum tON or tOFF are exceeded which causes the part to enter fold back mode (refer to Internal LDO, VCC UVLO, and Bias Input for details). In these cases, PWM is still maintained, but the frequency of operation is folded back (reduced) to maintain proper regulation. 7.4.5 DCM Mode DCM operation is employed in the LM76002-Q1/LM76003-Q1 when the load current is lower than ½ of the peak- to-peak inductor current. In DCM operation (also known as diode emulation mode), the LS FET is turned off when the inductor current drops below 0 A to keep operation as efficient as possible by reducing switching losses and preventing negative current conduction. In PWM operation, the frequency of operation is constant and fixed unless the load current is reduced below IPEAK_MIN, which causes the part to enter light load mode, or if the minimum tON or tOFF are exceeded, which cause the device to enter foldback mode. 7.4.6 Light Load Mode At light output current loads, PFM is activated for the highest efficiency possible. When the inductor current does not reach IPEAK_MIN during a switching cycle, the on-time is increased, and the switching frequency reduces as needed to maintain proper regulation. The on-time has a maximum value of 8 µs to avoid large output voltage ripple in dropout conditions. Efficiency is greatly improved by reducing switching and gate-drive losses. During light-load mode of operation the LM76002-Q1/LM76003-Q1 operates with a minimum quiescent current of 10 to 15 µA (typical). |
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