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CXLD140 датащи(PDF) 6 Page - Maxim Integrated Products |
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CXLD140 датащи(HTML) 6 Page - Maxim Integrated Products |
6 / 12 page 16µA IQ, 1.2A PWM DC-DC Step-Down Converters 6 _______________________________________________________________________________________ Detailed Description The MAX1556/MAX1557 synchronous step-down con- verters deliver a guaranteed 1.2A/600mA at output volt- ages from 0.75V to VIN. They use a 1MHz PWM current-mode control scheme with internal compensation, allowing for tiny external components and a fast transient response. At light loads the MAX1556/MAX1557 automat- ically switch to pulse-skipping mode to keep the quies- cent supply current as low as 16µA. Figures 2 and 3 show the typical application circuits. Control Scheme During PWM operation the converters use a fixed-fre- quency, current-mode control scheme. The heart of the current-mode PWM controller is an open-loop, multiple- input comparator that compares the error-amp voltage feedback signal against the sum of the amplified cur- rent-sense signal and the slope-compensation ramp. At the beginning of each clock cycle, the internal high-side p-channel MOSFET turns on until the PWM comparator trips. During this time the current in the inductor ramps up, sourcing current to the output and storing energy in the inductor’s magnetic field. When the p-channel turns off, the internal low-side n-channel MOSFET turns on. Now the inductor releases the stored energy while the current ramps down, still providing current to the output. The output capacitor stores charge when the inductor current exceeds the load and discharges when the inductor current is lower than the load. Under overload conditions, when the inductor current exceeds the cur- rent limit, the high-side MOSFET is turned off and the low-side MOSFET remains on until the next clock cycle. Pin Description PIN NAME FUNCTION 1 IN Supply Voltage Input. Connect to a 2.6V to 5.5V source. 2 GND Ground. Connect to PGND. 3SS Soft-Start Control. Connect a 1000pF capacitor (CSS) from SS to GND to eliminate input-current overshoot during startup. CSS is required for normal operation of the MAX1556/MAX1557. For greater than 22µF total output capacitance, increase CSS to COUT / 22,000 for soft-start. SS is internally discharged through 200 Ω to GND in shutdown. 4 OUT Output Sense Input. Connect to the output of the regulator. D1 and D2 select the desired output voltage through an internal feedback resistor-divider. The internal feedback resistor-divider remains connected in shutdown. 5 SHDN Shutdown Input. Drive SHDN low to enable low-power shutdown mode. Drive high or connect to IN for normal operation. 6 D2 OUT Voltage-Select Input. See Table 1. 7 PGND Power Ground. Connect to GND. 8LX Inductor Connection. Connected to the drains of the internal power MOSFETs. High impedance in shutdown mode. 9 INP Supply Voltage, High-Current Input. Connect to a 2.6V to 5.5V source. Bypass with a 10µF ceramic capacitor to PGND. 10 D1 OUT Voltage-Select Input. See Table 1. —EP Exposed Paddle. Connect to ground plane. EP also functions as a heatsink. Solder to circuit-board ground plane to maximize thermal dissipation. D1 D2 MAX1556 VOUT MAX1556A VOUT MAX1557 VOUT 00 Adjustable (VFB = 0.75) from 0.75V to VIN 3.3V Adjustable (VFB = 0.75) from 0.75V to VIN 0 1 3.3V 1.5V 1.5V 1 0 2.5V 1.2V 1.3V 1 1 1.8V 2.5V 1.0V Table 1. Output-Voltage-Select Truth Table A zero represents D_ being driven low or connected to GND. A 1 represents D_ being driven high or connected to IN. |
Аналогичный номер детали - CXLD140 |
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Аналогичное описание - CXLD140 |
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