Features

Output voltages from 1.1V to 5V Integrated high current gate drivers Up to two interleaved synchronization phase performance per IC Remote sensing and programmable active droop High precision voltage reference High speed transient response Programmable frequency from 200kHz to 2mHz Adaptive delay gate switch Integrated power good, ov, uv, enable/soft start

Function

Driving N-Channel MOSFET Operation Optimized for 12V Light Load High Efficiency Mode Over Current Protection Using MOSFET Sensing 28-Pin TSSOP Package Application: Logic Power Modular Power Supply

describe

The FAN 5092 is a synchronous multi-chip DC-DC controller IC providing high precision, programmable output voltage for all high current applications. Dual interleaved synchronous buck regulators with built-in current sharing are phase-in high current applications that provide the required fast transient response while minimizing external components. The FAN5092S can be paralleled for frequency and phase synchronization during maintenance and ensures current sharing in high power systems. The FAN5092 features remote voltage sensing, programmable activation of droop and leading response for optimal converter transient response with minimal output capacitance. It has integrated high-current gate driver switching with adaptive delay gates, requiring no external drive equipment. This enables switching frequencies up to 4MHz for ultra-high densities. The output voltage can be set from 1.1V to 5V with 0.5% accuracy. The FAN5092 uses a 12V power supply integrated to output over 150A of load current from A with a minimum external circuit. The FAN5092 also offers integrated features including power good, output enable/soft-start, undervoltage lockout, overvoltage protection, and current limit current sensing on each slice.

Application Information Operation: FAN5092 Controller The FAN5092 is a programmable synchronous polyphase DC-DC controller IC. It can operate as a single controller, and then a second fan 5092 can be modularly paralleled for higher current. When surrounded by appropriate external components, the FAN5092 can be configured to output currents greater than 120A. The FAN5092 operates as a fixed frequency pwm buck regulator in high efficiency mode (E*) at light loads. See the FAN5092 block diagram on page 7 for the main control loop. The fan5092 consists of two interleaved synchronous buck converters, implemented by summing mode control. Each phase has its own current feedback and voltage feedback. The two buck converters controlled by the FAN5092 are interleaved, that is, they are interleaved with each other. This will minimize the rms input ripple current and minimize the number of input capacitors required. It also doubles the effective switching frequency, improving transient response. FAN5092 implements "summation mode control", which is different from traditional voltage mode and current mode control. It outperforms allowing over a wide range of output loads and external components. The control loop of the regulator consists of two main parts: the analog control block and the digital control block. This analog part consists of a signal conditioning amplifier to form an input comparator, which is a digital control block. The signal conditioning part accepts the input of the current sensor and the voltage sensor. The voltage sensor is shared by the two pieces, and the current sensors are separated. The voltage sensor amplifies the difference between the VFB signal and the reference voltage from the DAC and presents the output separately to the comparator. The current control path of each slice uses the difference between its pgnd and sw pins when the low-side mosfet is turned on, the signal to the voltage amplifier through the mosfet and the resulting input current signal to the same input of its summing amplifier is certain gain. These, therefore, add up the two signals. This sum is then presented to a comparator that observes the oscillator ramp, which provides the main PWM control signal block to the digital control. The oscillator is ramped with each other so that the two slices are turned on alternately. The digital control block accepts the analog comparator input to the HDRV and LDRV output pins for each slice to provide the appropriate pulses. These outputs control external power mosfets.

Remote Voltage Sensing The FAN5092 has true remote voltage sensing capability, eliminating errors due to tracking resistors. With remote sensing, the VFB and AGND pins should be connected as Kelvin tracking pairs to adjustment points such as processor pins. The converter keeps the voltage at that point. The layout of these fields requires care; see layout guidelines in this data sheet. High Current Output Driver FAN5092 contains four high current output drivers using mosfet in push-pull configuration. Drivers for high-side MOSFETs use boot pins for input power and switch pins for return. The low side driver mosfet uses the vcc pin for input power and the pgnd return pin. Typically, the boot pins will use a charge pump. Note that the boot and VCC pins are separated from the chip's internal power and ground, bypass and agnd for switching noise immunity. The adaptive delay gate driver FAN5092 employs an advanced design that ensures minimal mosfet transition time when eliminating the water flow. It senses the state of the mosfet and adaptively adjusts the door drivers to ensure they never open at the same time. When the high-side mosfet turns off, the voltage on the power supply starts to drop. When the voltage here reaches about 2.5 volts, the low-side mosfet gate drive uses a delay of about 50 nsec. when? The low side mosfet is off and the voltage at the ldrv pin is sensed. When the voltage drops below about 2V, the gate drive of the high-side mosfet is used. MAXIMUM DUTY CYCLE To ensure current sensing and charge pump operation, the fan 5092 guarantees that the low side mosfet will be on for a specific part of each cycle. For low frequencies, the maximum duty cycle is approximately 90%. So at 250kHz, 4µsec period, the low side is at least 4µsec 8226 ; 10% = 400ns. At higher frequencies, this time may drop so low as to be ineffective.

The FAN5092 guarantees a minimum low-side turn-on time of about 330nsec, no matter what duty cycle this corresponds to. The current sensor connects the pgnd and sw pins of each phase to the Kelvin trace pair directly to the source and drain, respectively, of the appropriate low-side mosfet. Care needs to be taken in the layout of these venues; see this data sheet. The two independent current sensors of the current sharing fan 5092 operate independent current control loops to ensure that each of the two stages provides half of the total output current. Only if the rds of the low-side mosfet do not match. In normal use, two FAN5092S run in parallel. By connecting the ISHR pins together, both ICs will be forced to cycle in exactly the same way, ensuring all four stages. Short-Circuit Current Characteristics The FAN5092 short-circuit current characteristics include the event of a short circuit in the function that protects the DC-DC converter from damage. The short circuit limit is determined by the formula for each phase. Precision Current Sensing Tolerances Associated with Using MOSFET Current Using current sensing can avoid the sense resistor. E*-mode By putting the fan 5092 into E* mode. When the droop pin is pulled to the 5V bypass voltage, the "A" phase of the fan 5092 is fully closed and the number of gates is reduced by half to charge power consumption. The E*-mode can be implemented with the circuit shown

The internal voltage reference included in the fan5092 is an accurate bandgap voltage reference. Its internal resistance is precisely trimmed to provide a near-zero temperature coefficient (tc). Based on this reference is an integrated 5-bit output digital-to-analog converter. The DAC monitors 5 voltage identification pins, VID0-4, and adjusts the reference voltage from 1.100V to 1.850V in 25mV steps. The internal logic of the bypass reference fan5092 runs on 5v. The IC only operates at 12V and internally generates a 5V linear regulator with its output on the bypass pin. This pin should be bypassed with a 1µf capacitor to eliminate noise suppression. The bypass pin should not have any external load attached to it. The dynamic voltage scaling FAN5092 has an internal pull-up on its video line. External pull-ups should not be used. The fan 5092 can output a dynamically adjusted voltage to accommodate low power modes. The designer must ensure that the video lines are present simultaneously (less than 500nsec) to avoid error codes that produce undesired output voltages. The power good flag tracks the vid code, but has a 500 microsecond delay from high to low; this is long enough to ensure dynamic voltage scaling. The power good (pwrgd) FAN5092 power good function is designed to comply with the Pentium IV DC-DC converter specification and provides a continuous voltage monitor on the VFB pin. The circuit compares the vfb signal to the vref voltage and outputs a valid low interrupt signal to the CPU where the supply voltage deviates beyond its nominal setpoint. The output guarantees an open collector supply voltage within +8%/-18% above its nominal setting. The power of the good banner provides the control functions of the 5092 without the fan. Output Enable/Soft Start (Enable/SS) The FAN5092 will accept an open collector/TTL signal to control the output voltage. A low state disables the output voltage. When disabled, the pwrgd output is in the low state. Even if enable is not required in the circuit, a capacitor (usually 100nF) should be connected to this pin to soft start the switch. The soft-start capacitor can be approximated by the following equation. Input filter The design of a dc-dc converter can include the input inductance between the system mains and the converter input. This inductor is used to isolate the main inductor powered by the noise of the DC-DC switching section of the converter and to limit the inrush current of the input capacitor during power-up. The recommended value is 1.3 μh. It is necessary to install some low esr capacitors at the input to the converter. when the high-side mosfet switch is turned on. Because of the interleaving, the number of capacitors required is greatly reduced from that required for a monolithic buck converter. 3 x 1000 microF is shown, but the exact amount required will vary for output voltage and current, according to the formula for a four-bladed fan 5092, where dc is the duty cycle and DC=VOUT/VIN. Capacitor ripple current rating is a function of temperature, so the manufacturer should be contacted to find out the ripple current rating at the expected operating temperature. Details on input filter design.