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MAX5903ABEUT Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX5903ABEUT Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 14 page Turn-On and Turn-Off Delays After power is applied, or ON/OFF is released, there is a 150ms delay (tON) before the gate ramp is started. This delay is also the automatic restart time delay. In the event of a circuit-breaker condition or an over- temperature fault condition, the turn-off delay is less than 4µs. An undervoltage condition must exist for at least 10ms (tOFF) before the MAX5902/MAX5903 turns off the external MOSFET. ON/OFF must be held low for at least 10ms (tOFF) before the MAX5902/MAX5903 turns off the external MOSFET. Turn-off delay minimizes spurious shutdowns due to noisy signals or momentary voltage spikes, as well as preventing accidental reset- ting of the circuit-breaker latch (MAX5902L/MAX5903L). Thermal Shutdown A thermal shutdown feature helps protect the external MOSFET. If the die temperature of the MAX5902/ MAX5903 exceeds +125°C, the MOSFET is turned off. For accurate performance the MAX5902/MAX5903 must be in close thermal contact with the external MOS- FET. See the Layout Guidelines section for information. Due to the low power dissipation of the MAX5902/MAX5903, its junction temperature will typi- cally be within a few degrees of the MOSFET. All ver- sions of the MAX5902/MAX5903 automatically restart from a temperature fault when the junction temperature drops below +110°C. Undervoltage Lockout The MAX5902/MAX5903 turns off the external MOSFET if the magnitude of the input voltage is below the level set by ON/OFF for longer than 10ms (tOFF). If ON/OFF is left unconnected, the lockout voltage (VUVLO) defaults to 31.5V. VUVLO may also be set to any value within the power-supply range by using external resis- tors. To set the lockout voltage to a value between +9V and +72V use a resistor divider connected between VS and GND, with the center node of the divider connect- ed to ON/OFF. For example, use a 3kΩ resistor (R1 in Figure 3) from ON/OFF to GND and calculate the other resistor, R2, using: where VUVLO is the desired lockout voltage, and VON/OFF is the ON/OFF reference threshold specified in the Electrical Characteristics table (typically 1.26V). Figure 3 shows an example circuit with VUVLO set for +18V. To defeat the UVLO simply connect a single 100kΩ resistor between ON/OFF and VS, as shown in Figure 6. The Power-Good Output The power-good output, PGOOD (PGOOD), is open- drain and asserts when the external MOSFET is fully enhanced and VSD is less than the circuit-breaker threshold (VCB). For versions without the circuit-breaker function (MAX5902N/MAX5903N), PGOOD (PGOOD) asserts when the external MOSFET is fully enhanced. PGOOD (PGOOD) deasserts within 4µs when a circuit- breaker event occurs or if the die temperature exceeds +125°C. PGOOD (PGOOD) deasserts if VS < VUVLO for longer than 10ms or ON/OFF is held low for longer than 10ms. The MAX5902 PGOOD is active-low and the MAX5903 PGOOD is active-high. Both are open-drain n-channel MOSFETs with their sources connected to GND, and can withstand up to +72V. RR V V UVLO ON OFF 21 1 =× − ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ / +72V, SOT23/TDFN, Simple Swapper Hot-Swap Controllers 8 _______________________________________________________________________________________ HOT-SWAP CONTROLLER +9V TO +72V VS GND 100kΩ MAX5902 GND ON/OFF Figure 6. Defeating Undervoltage Lockout HOT-SWAP CONTROLLER 5V LOGIC GND LOGIC CONTROL OF 3.3V OR LESS MAY BE CONNECTED DIRECTLY TO THE MAX5902/MAX5903. FOR 5V LOGIC CONTROL INSERT A SERIES 47kΩ RESISTOR AS SHOWN. 47kΩ MAX5902 MAX5903 GND ON/OFF Figure 5. Logic Control |
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