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© 2008 Exar Corporation

4/15

Rev. 2.0.0

PIN ASSIGNEMENT

Fig. 3: SP6137 Pin Assignment

PIN DESCRIPTION

Name

Pin Number

Description

1

Bias Supply Input. Connect to external 5V supply. Used to power internal circuits and

low side gate driver.

GL

2

High current driver output for the low side NFET switch. It is always low if GH is high or

during a fault. Resistor pull down ensure low state at low voltage.

GND

3

Ground Pin. The control circuitry of the IC and lower power driver are referenced to this

pin. Return separately from other ground traces to the (-) terminal of COUT.

VFB

4

Feedback Voltage and Short Circuit Detection pin. It is the inverting input of the Error

Amplifier and serves as the output voltage feedback point for the Buck Converter. The

output voltage is sensed and can be adjusted through an external resistor divider.

Whenever VFB drops 0.25V below the positive reference, a short circuit fault is detected

and the IC enters hiccup mode.

COMP

5

Output of the Error Amplifier. It is internally connected to the inverting input of the

PWM comparator. An optimal filter combination is chosen and connected to this pin and

either ground or VFB to stabilize the voltage mode loop.

UVIN

6

UVLO input for VIN voltage. Connect a resistor divider between VIN and UVIN to set

minimum operating voltage.

SS

7

Soft Start. Connect an external capacitor between SS and GND to set the soft start rate

based on the 10μA source current. The SS pin is held low via a 1mA (min) current

during all fault conditions.

SWN

8

Lower supply rail for the GH high-side gate driver. Connect this pin to the switching

node at the junction between the two external power MOSFET transistors.

GH

9

High current driver output for the high side NFET switch. It is always low if GL is high or

during a fault. Resistor pull down ensure low state at low voltage.

BST

10

High side driver supply pin. Connect BST to the external boost diode and capacitor as

shown in the Typical Application Circuit on page 1. High side driver is connected

between BST pin and SWN pin.