Features: Ultra low voltage drop, 0.4V, 3A typ. Remote operation Fast transient response Load regulation: 0.05% typ. 0.5% initial accuracy On-chip thermally limited 5-pin TO-252 DPAK and TO-263 packages

Application: Support GTL+ bus power low voltage logic power embedded processor supply faceted regulator 2.5V and 1.8V logic family DDR termination power supply

Description: The FAN1582 , FAN 1582-1.5 and FAN1582-2.5 are ultra low drain regulators with 3A output current capability. These devices are optimized for low voltage applications including VTT bus termination, where transient response and minimum input voltage are critical. The FAN1582 is ideal for low voltage microprocessor applications requiring a regulated 1.3V to 5.7V output, with a power input fan the 1582-1.5 provides a fixed 1.5V 3 GTL+ bus VTT termination current capability. The FAN1582-2.5 provides fixed 2.5V and 3A current capability for logic IC operations and processors while minimizing overall power consumption. The current limit ensures that the short-circuit current is controlled. On-chip thermal limiting prevents any combination of overload and ambient temperature that would result in excessive junction temperatures. The FAN1582 series regulators are available in 5-pin to-252 dpak and to-263 power packs.

General FAN1582, FAN1582-1.5 and FAN1582-2.5 are for GTL+VTT terminal and logic applications. These units are short-circuit protected and provide thermal shutdown for connection temperatures exceeding approximately 150°C. Fan 1582 series provides low voltage drop and fast transient response. Frequency compensation is used low while remaining stable. This addresses the need for low-voltage, high-speed microprocessor buses such as GTL+. The VIN and VCNTL functionality of the FAN1572 is maximized using a dual power supply approach. efficiency. The collector of the power supply unit is taken out to the VIN pin to minimize high current loads. VCNTL provides the circuit and driver for the power output NPN transistor for the control. VCNTL should be at least 1.2V above the output voltage. Special care is taken to ensure that there are no problems with unclear consequences. The output voltage does not turn on until both supplies are active. If the control voltage is first, the output current is typically limited to about 3.0 mA until the power supply input voltage rises. If the power supply input voltage rises first, the output does not conduct until the control voltage rises. The output may not appear unregulated. The FAN1582 can also be used as a single-supply device control and power input connected together. In this mode, the voltage drop is determined by the minimum control voltage. Stability The FAN1582 series requires an output capacitor for frequency compensation. A 22µF solid tantalum or 100µF aluminum electrolytic is recommended for stability. Their frequency compensation devices utilize low esr capacitors to optimize frequency response.

In general, it is recommended to use capacitors with ESR less than 0.3Ω. It is also recommended to use bypass capacitors such as 22µf tantalum or 100µf aluminum to adjust the pins of the fan 1582 for low ripple and fast transient response. When these bypass capacitors are not used on the adjust pins, smaller values of output capacitors provide the same good results. A graph showing the stability of the output capacitor can find esr vs. load current characteristics under typical performance. Protection Diodes In normal operation, the FAN1582 series does not require any protection diodes. For the fan 1582, the internal resistance limits the internal current path on the adjustment pins. Therefore, even with bypass capacitors on the adjustment pins, no protection diodes are needed to ensure device safety in short circuit conditions. Protection diodes are usually not required between the input and output pins. The input and output pins on the fan 1582 series can handle microsecond inrush currents of 50A to 100A. Even with large output values capacitors have difficulty getting those inrush values for normal operation currents. Damage occurs only when the output capacitance value is large, such as 1000 microF to 5000 microF, and the input pin is short-circuited to ground instantaneously. A crowbar circuit at the input can generate current; diodes from output to input are recommended, as shown. Normally, normal power cycling or the system "hot swapping" will not draw enough current to cause any damage.

Ripple Suppression In applications requiring improved ripple suppression, a capacitor bypassed from the fan 1582 adjust pin to ground reduces the output ripple by a ratio of Vout/1.25V. The impedance of the trim pin capacitor at the ripple frequency should be less than the value of r1 (usually 100Ω to 120Ω in the feedback divider network in the figure). Therefore, the value of 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 adjustment 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 picture). Placing a resistor r1 between these two terminals causes a constant current to flow through R1 and down through R2 to set the total output voltage. Typically, this current is specified as a minimum load current of 10mA. The current drawn from the regulation pin plus the current from r1 is typically 50 microamps. Its output voltage contribution is small and only needs to be considered when a very precise output voltage setting is required.

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 the output pin. If the load exceeds 1" outside of the fan 1582, it may be necessary to increase the load capacitance to ensure stability. Thermal Factor The FAN1582 series protects itself from overload conditions with an internal power supply and thermal limiting circuit. However, for normal continuous load conditions, the maximum Junction temperature rating. It is important to consider all sources of thermal resistance from connection to ambient. These sources include resistance to the case, interface resistance between case and heat sink, and heat sink resistance. Thermal resistance specifications more accurately reflect device temperature and ensure safe operating temperature. The electrical characteristics section provides individual thermal resistance and maximum junction temperature for control circuits and power transistors. Calculate the maximum junction temperature for both sections to ensure that the limits are reached.

For example, using the fan1582m-1.5 to generate a 3.3V supply (3.2V to 3.6V) is 3A when the voltage is 1.5V±2%.

The junction temperature is below the maximum ratings. The IC specifies a thermal resistance connected to the case connected to the bottom of the case just below the die. This is the path of least resistance for heat flow. Proper installation ensures that from this area to the radiator. The chassis-to-heatsink interface is recommended for use with thermally conductive materials. Use thermally conductive spacers if the equipment enclosure must be electrically isolated and include resistance to its contribution to total heat.