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PM6675 Datasheet(PDF) 17 Page - STMicroelectronics |
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PM6675 Datasheet(HTML) 17 Page - STMicroelectronics |
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17 / 47 page  Obsolete Product(s) - Obsolete Product(s) Obsolete Product(s) - Obsolete Product(s) PM6675 Device description 17/47 6.1.1 Constant-On-Time architecture Figure 6 shows the simplified block diagram of the Constant-On-Time controller. The switching regulator of the PM6675 controls a one-shot generator that initiates the high- side MOSFET when the following conditions are simultaneously satisfied: the PWM comparator is high (i.e. output voltage is lower than Vr = 0.6V), the synchronous rectifier current is below the current limit threshold and the minimum off-time has expired. A minimum Off-Time contraint (300ns typ.) is introduced to assure the boot capacitor charge and allow inductor valley current sensing on low-side MOSFET. A minimum On-Time is also introduced to assure the start-up switching sequence. Once the On-Time has timed out, the high side switch is turned off, while the synchronous rectifier is ignited according to the anti-cross conduction management circuitry. When the output voltage reaches the valley limit (determined by internal reference Vr = 0.6V), the low-side MOSFET is turned off according to the anti-cross conduction logic once again, and a new cycle begins. Figure 6. Switching section simplified block diagram + - HS HS driver driver Level Level shifter shifter LS LS driver driver Q Q R S Ton Ton--min min Anti cross- conduction circuitry Toff Toff--min min Q R S + - PWM Comparator PWM Comparator Positive Current Limit comparator Positive Current Limit comparator 0.6V 0.6V Q Q R S + _ Min Min fsw fsw counter counter Zero Zero--crossing crossing Comparator Comparator bandgap bandgap 1.236V 1.236V PHASE PHASE PGND PGND LGATE LGATE BOOT BOOT CSNS CSNS COMP COMP gm gm Integrator Integrator VSNS VSNS VBG VBG VBG VBG PULSE PULSE -- SKIP SKIP VSEL VSEL VSEL<4V 1-Shot generator Ton Ton VSNS VSNS VOSC VOSC 0.6V 0.6V 100uA 100uA 500mV 2.5V 2.5V + - - - + + HGATE HGATE VREF VREF SGND SGND VOSC VOSC VOSC VOSC VCC VCC + - HS HS driver driver Level Level shifter shifter LS LS driver driver Q Q R S Ton Ton--min min Anti cross- conduction circuitry Toff Toff--min min Q R S + - PWM Comparator PWM Comparator Positive Current Limit comparator Positive Current Limit comparator 0.6V 0.6V Q Q R S + _ Min Min fsw fsw counter counter Zero Zero--crossing crossing Comparator Comparator bandgap bandgap 1.236V 1.236V PHASE PHASE PGND PGND LGATE LGATE BOOT BOOT CSNS CSNS COMP COMP gm gm Integrator Integrator VSNS VSNS VBG VBG VBG VBG PULSE PULSE -- SKIP SKIP VSEL VSEL VSEL<4V 1-Shot generator Ton Ton VSNS VSNS VOSC VOSC 0.6V 0.6V 100uA 100uA 500mV 2.5V 2.5V + - - - + + HGATE HGATE VREF VREF SGND SGND VOSC VOSC VOSC VOSC VCC VCC |
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