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FAN5601 Fiches technique(PDF) 10 Page - Fairchild Semiconductor |
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FAN5601 Fiches technique(HTML) 10 Page - Fairchild Semiconductor |
10 / 15 page 10 www.fairchildsemi.com FAN5601 Rev. 1.0.5 Block Diagram Detailed Description The FAN5601 switched capacitor DC/DC converter automati- cally configures switches to achieve a high efficiency and pro- vides a regulated output voltage by means of pulse skipping, pulse frequency modulation (PFM). An internal soft start circuit prevents excessive inrush current drawn from the supply. Each switch is split into three segments. Based on the values of VIN, VOUT and IOUT, an internal circuitry determines the number of segments to be used to reduce current spikes. Step-Down Charge Pump Operation When VIN ≥ 2.22 × VOUT, a 2:1 configuration shown in Fig.1(A) is enabled. The factor 0.9 is used instead of 1 in order to account for the effect of resistive losses across the switches and to accommodate hysteresis in the voltage detector comparator. Two phase non-overlapping clock signals are generated to drive four switches. When switches 1 and 3 are ON, switches 2 and 4 are OFF and CB is charged. When switches 2 and 4 are ON, switches 1 and 3 are OFF, charge is transferred from CB to COUT. When VIN <2.22 × VOUT, a 1:1 configuration shown in Fig. 1(B) is enabled. In the 1:1 configuration switch 3 is always OFF and the switch 4 is always ON. At 1.6V output setting the configura- tion changes from 2:1 to 1:1 at VIN = 3.56V. At 1.3V output set- ting the change occurs at VIN = 3.06V. Pulse-skipping PFM and Fractional Switch Operation When the regulated output voltage reaches its upper limit, the switches are turned off the output voltage reaches its lower limit. Considering a step-down 2:1 mode of operation, 1.6V output as an example, when the output reaches about 1.62V(upper limit), the control logic turns off all switches. Switching stops com- pletely. This is pulse-skipping mode. Since the supply is isolated from the output, the output voltage will drop. Once the output is dropped to about 1.58V(lower limit), the device will return to reg- ular switching mode with one quarter of each switch turning on first. Another quarter of each switch will be turned on if VOUT cannot reach regulation by the time of arrival of the third charge cycle. Full switch operation occurs only during startup or under heavy load condition, when half switch operation cannot achieve regulation within seven charge cycles. Soft Start The soft-start feature limits inrush current when the device is ini- tially powered up and enabled. The reference voltage is used to control the rate of the output voltage ramp-up to its final value. Typical start-up time is 1ms. Since the rate of the output voltage ramp-up is controlled by an internally generated slow ramp, pulse-skipping occurs and inrush current is automatically lim- ited. UVLO + - SHUTDOWN CONTROL LOGIC CONFIGURATION PULSE_SKIP SHORT_CKT. + - + - + - THERMAL SHUTDOWN IN OUT Vref RAMP FB OUTPUT 150mV 1V 0.5* INPUT VOLTAGE REF. SOFT START Vref RAMP OSCILLATOR (2MHz) C+ C- ENABLE V IN GND. D R I V E R S 0.25SW1 0.25SW1 0.25SW4 0.25SW4 0.5SW4 0.25SW3 0.25SW3 0.5SW3 0.5SW2 0.25SW2 0.25SW2 0.5SW1 FB VOUT |
Numéro de pièce similaire - FAN5601_05 |
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Description similaire - FAN5601_05 |
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