RC5052 查看數據表（PDF） - Fairchild Semiconductor

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RC5052

High Performance Programmable Synchronous DC-DC Controller for Low Voltage Microprocessors

Fairchild Semiconductor 

RC5052

Test Parameters

PRODUCT SPECIFICATION

tR

10%

90%

2V

tF

90%

2V

HIDRV

10%

tDT

tDT

2V

2V

LODRV

Figure 3. Output Drive Timing Diagram

Application Information

The RC5052 Controller

The RC5052 is a programmable synchronous DC-DC con-

troller IC optimized for 12V main power. It may also be used

in a 5V main power circuit when the crowbar and additional

programmability of the RC5052 are desired. When designed

around the appropriate external components, the RC5052 can

be configured to deliver more than 16A of output current, as

appropriate for the Katmai and Coppermine and other pro-

cessors. The RC5052 functions as a fixed frequency PWM

step down regulator.

Main Control Loop

Refer to the RC5052 Block Diagram on page 1. The RC5052

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 IFB (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 IFB 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 comparator look-

ing 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 section

whose function is to set the point at which the RC5052 current

limit comparator disables the output drive signals to the external

power MOSFETs.

High Current Output Drivers

The RC5052 contains two identical high current output drivers

that utilize high speed bipolar transistors in a push-pull config-

uration. The drivers’ power and ground are separated from

the chip’s power and ground for switching noise immunity.

The high-side driver’s power supply pin, VCCQP, 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. The low-side driver’s power supply pin, VCCP,

is supplied from the same source as VCCQP. The VCCQP

pin should be run as a charge pump for +12V Main Power, as

shown in Figure 1.

Internal Voltage Reference

The reference included in the RC5052 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. The

DAC monitors the 5 voltage identification pins, VID0-4. When

the VID4 pin is at logic HIGH, the DAC scales the reference

voltage from 2.0V to 3.5V in 100mV increments. When VID4

is pulled LOW, the DAC scales the reference from 1.30V to

2.05V in 50mV increments. All VID codes are available,

including those below 1.80V. The output voltage may be

changed while the converter is on by changing the VID

codes; however, it is necessary to do so in 1-bit steps, to

avoid triggering the overvoltage protection.

Power Good (PWRGD)

The RC5052 Power Good function is designed in accordance

with the Pentium II 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 the

power supply voltage deviate more than ±12% of its nominal

setpoint. The output is guaranteed open-collector high when

the power supply voltage is within ±7% of its nominal setpoint.

12

REV. 1.3.2 8/27/01

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