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FAN5070 数据表(PDF) 8 Page - Fairchild Semiconductor |
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FAN5070 数据表(HTML) 8 Page - Fairchild Semiconductor |
8 / 14 page FAN5070 8 REV. 1.0.1 8/7/01 Application Information The FAN5070 Controller The FAN5070 is a programmable synchronous DC-DC con- troller IC. When designed around the appropriate external components, the FAN5070 can be configured to deliver more than 28A of output current, as appropriate for Intel’s VRM8.5, and other processors. The FAN5070 functions as a fixed frequency PWM step down regulator. Main Control Loop Refer to the FAN5070 Block Diagram on page 1. The FAN5070 implements “summing mode control,” which is different from both classical voltage-mode and current-mode control. It provides superior performance to either by allowing a large converter bandwidth over a wide range of output loads. The control loop of the regulator contains two main sections: the analog control block and the digital control block. The analog section consists of signal conditioning amplifiers feeding into a comparator which provides the input to the digital control block. The signal conditioning section accepts input from the DROOP (current feedback) and VFB (voltage feedback) pins and sets up two controlling signal paths. The first, the voltage control path, amplifies the difference between the VFB signal and the reference voltage from the DAC and presents the output to one of the summing amplifier inputs. The second, current control path, takes the difference between the DROOP and SW pins when the high-side MOSFET is on, reproducing the voltage across the MOSFET and thus the input current; it presents the resulting signal to another input of the summing amplifier. These two signals are then summed together. This output is then presented to a com- parator looking at the oscillator ramp, which provides the main PWM control signal to the digital control block. The digital control block takes the analog comparator input and the main clock signal from the oscillator to provide the appropriate pulses to the HIDRV and LODRV output pins. These two outputs control the external power MOSFETs. There is an additional comparator in the analog control sec- tion whose function is to set the point at which the FAN5070 current limit comparator disables the output drive signals to the external power MOSFETs. High Current Output Drivers The FAN5070 contains two identical high current output drivers that utilize high speed bipolar transistors in a push- pull configuration. The drivers’ power and ground are sepa- rated from the chip’s power and ground for switching noise immunity. The power supply pin, VCCP, is supplied from an external 12V source through a series resistor. The resulting voltage is sufficient to provide the gate to source drive to the external MOSFETs required in order to achieve a low RDS,ON. Internal Voltage Reference The reference included in the FAN5070 is a precision band- gap voltage reference. Its internal resistors are precisely trimmed to provide a near zero temperature coefficient (TC). Based on the reference is the output from an integrated 5-bit DAC. In the FAN5070, the DAC monitors the 5 voltage identifica- tion pins, VID0-4, and scales the voltage from 1.050V to 1.825V in 25mV steps according to Table I. Power Good (PWRGD) The FAN5070 Power Good function is designed in accor- dance with VRM8.5 and DC-DC converter specifications and provides a continuous voltage monitor on the VFB pin. The circuit compares the VFB signal to the VREF voltage and outputs an active-low interrupt signal to the CPU should be more than +14% from (VVID + 80mV), or less than –14% from (VVID – 120mV). The Power Good flag provides no other control function to the FAN5070. Output Enable/Soft Start (ENABLE/SS) The FAN5070 will accept an open collector/TTL signal for controlling the output voltage. The low state disables the out- put voltage. When disabled, the PWRGD output is in the low state. Even if an enable is not required in the circuit, this pin should have attached a capacitor (typically 100nF) to soft- start the switching. Over-Voltage Protection The FAN5070 continuously monitors the output voltage for protection against over-voltage conditions. If the voltage at the VFB pin exceeds approximately 2.5V, an OVP circuit forces the low-side MOSFET on, over-riding all other conditions. The OVP circuit remains active, and the low-side MOSFET remains on, until the VFB voltage drops below approximately 2.1V. The OVP circuit is functional even during startup; thus, protection is provided even during startup with a shorted high-side MOSFET. Oscillator The FAN5070 oscillator section uses a fixed frequency of operation of 300KHz. |
类似零件编号 - FAN5070 |
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类似说明 - FAN5070 |
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