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MAX15000A Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX15000A Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 18 page Detailed Description The MAX15000/MAX15001 current-mode PWM con- trollers are ideal for isolated and nonisolated power- supply applications. The devices offer an accurate input startup voltage programmable through the UVLO/EN input. This feature prevents the power supply from entering a brownout condition in case the input voltage sags below its minimum value. This is important since switching power supplies increases their input supply current as the input voltage drops to keep the output power constant. In addition to this externally adjustable UVLO feature, the MAX15000 also offers a bootstrap UVLO with a large hysteresis (11.9V) and very low startup and operating current, which result in an efficient universal input power supply. The switching frequency of the MAX15000/MAX15001 is programma- ble with an external resistor. The MAX15000 is well suited for universal input (recti- fied 85VAC to 265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX15001 is well suited for low-input voltage (9.5VDC to 24VDC) power sup- plies. The devices include an internal clamp at IN to prevent the input voltage from exceeding the absolute maximum rating (see Note 2 at the end of the Electrical Characteristics table). The input is clamped when the devices are started with a bleed resistor (R1 in Figure 1) from a high input voltage and the UVLO/EN input is low. The clamp can safely sink up to 2mA current. Power supplies designed with the MAX15000 use a high-value startup resistor R1 that charges a reservoir capacitor C1 (see Figure 1). During this initial period, while the voltage is less than the internal bootstrap UVLO threshold, the device typically consumes only 50µA of quiescent current. This low startup current and the large bootstrap UVLO hysteresis help to minimize the power dissipation across R1 even at the high end of the universal AC input voltage (265VAC). The MAX15000/MAX15001 include a cycle-by-cycle current limit that turns off the gate drive to the external MOSFET whenever the internally set threshold of 1V is exceeded. When using the MAX15000 in the boot- strapped mode, if the power-supply output is shorted, the tertiary winding voltage will drop below the internal- ly set threshold causing the UVLO to turn off the gate drive to the external power MOSFET. This will reinitiate a startup sequence with soft-start. Current-Mode PWM Controllers with Programmable Switching Frequency 8 _______________________________________________________________________________________ 8 9 10 3 2 1 UVLO/EN IN 7 4 VCC NDRV GND UFLG FB COMP 6 5 RT CS T1 R3 R2 R12 R1 R4 C5 C2 C2 C1 C4 D2 D1 C6 R11 VSUPPLY 0V R13 R14 VOUT R15 Q1 MAX15000 Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage |
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