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MAX8640YEXT12+T Datasheet(PDF) 5 Page - Maxim Integrated Products |
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MAX8640YEXT12+T Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 11 page Tiny 500mA, 4MHz/2MHz Synchronous Step-Down DC-DC Converters _______________________________________________________________________________________ 5 PIN NAME FUNCTION 1LX Inductor Connection to the Internal Drains of the p-channel and n-channel MOSFETs. High impedance during shutdown. 2, 5 GND Ground. Connect these pins together directly under the IC. 3 OUT Output Sense Input. Bypass with a ceramic capacitor as close as possible to pin 3 (OUT) and pin 2 (GND). OUT is internally connected to the internal feedback network. 4 SHDN Active-Low Shutdown Input. Connect to IN or logic-high for normal operation. Connect to GND or logic-low for shutdown mode. 6IN Supply Voltage Input. Input voltage range is 2.7V to 4.9V. Bypass with a ceramic capacitor as close as possible to pin 6 (IN) and pin 5 (GND). Pin Description Detailed Description The MAX8640Y/MAX8640Z step-down converters deliv- er over 500mA to outputs from 0.8V to 2.5V. They utilize a proprietary hysteretic PWM control scheme that switches at up to 4MHz (MAX8640Z) or 2MHz (MAX8640Y), allowing some trade-off between efficien- cy and size of external components. At loads below 100mA, the MAX8640Y/MAX8640Z automatically switch to pulse-skipping mode to minimize the typical quies- cent current (24µA). Output ripple remains low at all loads, while the skip-mode switching frequency remains ultrasonic down to 1mA (typ) loads. Figure 1 is the simplified functional diagram. Control Scheme A proprietary hysteretic PWM control scheme ensures high efficiency, fast switching, fast transient response, low output ripple, and physically tiny external compo- nents. This control scheme is simple: when the output voltage is below the regulation threshold, the error comparator begins a switching cycle by turning on the high-side switch. This switch remains on until the mini- mum on-time expires and the output voltage is above the regulation threshold or the inductor current is above the current-limit threshold. Once off, the high-side switch remains off until the minimum off-time expires and the output voltage falls again below the regulation threshold. During the off period, the low-side synchro- nous rectifier turns on and remains on until either the high-side switch turns on again or the inductor current approaches zero. The internal synchronous rectifier eliminates the need for an external Schottky diode. Voltage-Positioning Load Regulation The MAX8640Y/MAX8640Z utilize a unique feedback network. By taking DC feedback from the LX node, the usual phase lag due to the output capacitor is removed, making the loop exceedingly stable and allowing the use of very small ceramic output capacitors. This configuration yields load regulation equal to the inductor’s series resistance multiplied by the load current. This voltage-positioning load regulation greatly reduces overshoot during load transients, effectively halving the peak-to-peak output-voltage excursions compared to tra- ditional step-down converters. See the Load-Transient Response in the Typical Operating Characteristics. Shutdown Mode Connecting SHDN to GND or logic low places the MAX8640Y/MAX8640Z in shutdown mode and reduces supply current to 0.1µA (typ). In shutdown, the control circuitry and internal MOSFET switches turn off and LX becomes high impedance. Connect SHDN to IN or logic high for normal operation. PWM LOGIC MAX8640Y MAX8640Z GND LX IN SHDN 0.6V OUT Figure 1. Simplified Functional Diagram |
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