feature

Ultra Low Voltage Drop, 0.4V, 3A Typical Remote Operation Fast Transient Response Load Regulation: 0.05% Typical Initial Accuracy 0.5% Chip Thermal Limits 5-Pin to 263 Package

application

Support GTL+ bus power low voltage logic power embedded processor power facet regulator 2.5V and 1.8V logic series DDR terminal power supply

illustrate

The FAN1582 , FAN1582-1.5 and FAN1582-2.5 are ultra high performance low dropout regulators with 3A output current capability. These devices are optimized for low voltage applications, including VTT bus termination, where response and minimum input voltage are critical. The FAN1582 is ideal for low voltage microprocessor applications that require a regulated 1.3V to 5.7V output with a 1.75V to 6.5V power supply input. FAN1582-1.5 provides fixed 1.5V and 3A current capability for GTL+ bus VTT termination. The FAN1582-2.5 provides a fixed 2.5V and 3A current capability for logic IC operations and processors while minimizing total power consumption. The current limit ensures that the short-circuit current is controlled. Onchip thermal limiting provides combined overload and ambient temperature protection from excessive junction temperatures. The FAN1582 provides a 5-pin to 263 power pack.

Detailed operation

Fan 1582, Fan 1582-1.5 and Fan 1582-2.5 are three termination regulators optimized for GTL+VTT termination and logic applications. These devices are short-circuit protected and provide thermal shutdown to shut down the regulator when the junction temperature exceeds approximately 150°C. The FAN1582 series offers low voltage drop and fast transient response. Frequency compensation uses low ESR capacitors while maintaining stability. This is critical for addressing the needs of low-voltage, high-speed microprocessor buses like GTL+. The VIN and VCNTL functions of the FAN1572 utilize a dual power supply approach to maximize efficiency. The collector of the power supply is routed to the VIN pin to minimize internal power dissipation under high current loads. VCNTL provides power for the control circuit and the driver transistors of the output NPN. VCNTL should be at least greater than the output voltage. Special care was taken to ensure that there were no supply sequence issues. The output voltage does not turn on until both supplies are operating. If the control voltage rises first, the output current is usually limited to around 3.0mA until the power input voltage rises. If the power supply input voltage rises first before the control voltage arrives, the output will not turn on. The output can never go uncontrolled.

Fan 1582 can also be connected together as the control and power input for a single power supply. In this mode, the dropout rate is controlled by the voltage. Stability The FAN1582 series requires an output capacitor as part of the frequency compensation. A 22µF solid tantalum or 100µF aluminum electrolytic is recommended on the output to ensure stability. The frequency compensation of these devices optimizes the frequency low ESR capacitor response. In general, it is recommended to use capacitors with ESR less than 0.3Ω. It is also recommended to use a bypass capacitor, such as 22µF tantalum or 100µF aluminum, on the FAN1582 for low ripple and fast transient response. If these bypass capacitors are not used for the regulation pins, smaller values of output capacitance provide equally good results. A graph showing the stability of the output capacitor ESR versus load current is shown in the figure. The FAN1582 series does not require any protection diodes for normal operation. For the fan 1582, internal resistors limit the internal current path on the adjustment pins. Therefore, even with bypass capacitors on the regulation pins, there is no need to use protection diode shorts for device safety.

Protection diodes between input and output pins are usually not required. Internal diodes between the input terminals of the FAN1582 series output pins can handle microsecond surge currents from 50A to 100A. Even with large value output capacitors, it is difficult to obtain inrush current values during normal operation. Only with large values of output capacitors, such as 1000µF to 5000µF, the input pins are momentarily shorted to ground and may be damaged. Because the crowbar circuit input can draw these levels of current, a diode is recommended from the input to the output as shown. Typically, normal power cycling or system "hot" "plugging" does not draw currents large enough to cause damage.

Ripple suppression reduces output ripple/1.25V from the fan 1582's adjust pin to ground in applications where improved ripple suppression is required. The adjust pin capacitor should be less than the value of R1 in the feedback at the ripple frequency (typically in the range of 100Ω to 120Ω ) in the segmentation network in the figure. Therefore the required trim pin capacitor is a function of the input ripple frequency. For example, if R1 is equal to 100Ω and the ripple frequency is equal to 120Hz, the trim pin capacitor should be 22µF. At 10kHz, only 0.22µF is required.

The output voltage FAN1582 regulator generates a 1.25V reference voltage between the output pin and the adjust pin (see figure). Placing a resistor between these two R1 terminals allows constant current to flow through R1 and then through R2 to set the total output voltage. Typically, this current is the specified minimum load current of 10mA. Adjust pin current plus R1, typically 50µA. The output voltage contribution is very small, and the output voltage only needs to be set very accurately.

The load regulation FAN1582 series provides true remote sensing, eliminating output voltage errors due to tracking resistors. To utilize remote sensing, connect the VSENSE pin directly to the load, not at the output. If the load is larger than 1" from the fan 1582, it may be necessary to increase the load capacitance to ensure stability. Thermal Factor The FAN1582 series overload protects the internal power and thermal limiting circuit conditions. However, for normal continuous load conditions, the maximum junction temperature rating must not be exceeded. It is important to consider all sources of thermal resistance from the junction to the surroundings. These sources include the resistance connected to the case, the interface resistance of the case to the heat sink, and the heat sink resistance. To more accurately reflect device temperature and ensure safety, thermal resistance specifications have been established for operating temperature. The Electrical Characteristics section provides individual thermal resistances and maximum junction temperatures for control circuits. And power transistors. Calculate the maximum junction temperature for both sections to ensure both meet thermal limits. For example, use the FAN1582M-1.5 to generate 3A from a 3.3V supply (3.2V to 3.6V) at 1.5V ± 2%.

Suppose:

VIN = 3.6V worst case VOUT = 1.47V worst case IOUT = 3A continuous TA = 70 degrees Celsius ΘJCA = 5°C/W (assuming both heat sink and thermally conductive material) The power dissipation in this application is: PD =(VIN-OUT)*(IN)=(3.6-1.47)*(3)=6.39W From the spec sheet, TJ=TA+(PD)*(ΘCA+ΘJC)=70+(6.39)*( 5+3) = 121°C junction temperature below maximum rating.

The thermal resistance from the connector to the case is determined by the IC connector directly below the bottom of the case. This is the path of least resistance for heat flow. Correct installation ensures optimum heat flow to the radiator area. Use of thermally conductive material It is recommended to use material at the interface of the case to the heat sink. If electrical isolation is required on the enclosure, including the contribution to the total thermal resistance.