FAN5182_08 Datasheet, PDF (3/19 Pages) Fairchild Semiconductor – Adjustable Output, 1-, 2-, or 3-Phase Synchronous Buck Controller

Pin Assignments
Figure 2. Pin Assignments
Pin Definitions
Pin #
1
2
Name
VCC
FBRTN
3
FB
4
COMP
5
PWRGD
6
EN
7
DELAY
8
RT
9 RAMPADJ
10
ILIMIT
11
CSREF
12
CSSUM
13 CSCOMP
14
GND
15–17 SW3 - SW1
18–20
PWM3 -
PWM1
Description
Supply Voltage for the Device.
Feedback Return. Voltage error amplifier reference for remote sensing of the output voltage.
Feedback Input. Error amplifier input for remote sensing of the output voltage. An external
resistor divider between the output and FBRTN connected to this pin sets the output voltage.
This pin is also the reference point for the power-good and crowbar comparators.
Error Amplifier Output and Compensation Pin.
Power Good Output. Open-drain output that signals when the output voltage is outside the
proper operating range.
Power Supply Enable Input. Pulling this pin to GND disables the PWM outputs and pulls the
PWRGD output low.
Soft-Start Delay and Current Limit Latch-Off Delay Setting Input. An external resistor and
capacitor connected between this pin and GND sets the soft-start ramp-up time and the over-
current latch-off delay time.
Frequency Setting Resistor Input. An external resistor connected between this pin and GND
sets the oscillator frequency of the device.
PWM Ramp Current Input. An external resistor from the converter input voltage to this pin
sets the internal PWM ramp.
Current-Limit Set point / Enable Output. An external resistor connected from this pin to GND
sets the current limit threshold of the converter. This pin is actively pulled low when the EN
input is low, or when VCC is below its UVLO threshold, to signal to the driver IC that the driver
high-side and low-side outputs should go low.
Current-Sense Reference Voltage Input. The voltage on this pin is used as the reference for
the current-sense amplifier. Connect this pin to the common point of the output inductors.
Current-Sense Summing Node. External resistors from each switch node to this pin sum the
average inductor currents to measure the total output current.
Current-Sense Compensation Point. A resistor and a capacitor from this pin to CSSUM
determine the gain of the current sense amplifier.
Ground. All internal biasing and logic output signals are referenced to this ground.
Current Balance Inputs. These are inputs for measuring the current level in each phase. The
SW pins of unused phases should be connected to ground.
Logic-Level PWM Outputs. Each output is connected to the input of an external MOSFET
driver, such as the FAN5109. Connecting the PWM3 output to GND causes that phase to
turn off, allowing the FAN5182 to operate as a 1- or 2-phase controller. Do not connect
PWM2 to ground for 1-phase operation.
© 2005 Fairchild Semiconductor Corporation
FAN5182 • Rev. 1.1.3
3
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