6

HV310

From the second equation for an over voltage set point of

65V, the value of R3 may be calculated.

OV

R3 = (1.26 • 500K) / 65 = 9.69 kΩ

The closest 1% value is 9.76kΩ.

From the first equation for an under voltage set point of 35V,

the value R2 can be calculated.

UV

R2 = (1.16 • 500K) / 35 – 9.76kΩ = 6.81kΩ.

The closest 1% value is 6.81kΩ.

Then R1 = 500K – (R2 + R3) = 483kΩ

The closest 1% value is 487kΩ.

Undervoltage/Overvoltage Operation

Current Limit

The current limit magnitude above which the current will

not be allowed to rise during startup is programmed using a

sense resistor connected from the SENSE pin to VEE pin.

For example to program a current limit of 1.0A, one would

choose a resistor as follows:

R

R

R

GND

Pass

Transistor

OFF

ON

Pin #

Function Description

1

PWRGD

Ths pin is held in Hi-Z state on initial power application and pulls low when the external MOSFET

is fully turned on. This pin may be used as an enable control when connected directly to a PWM

power module.

2

OV

This pin, when raised above its high threshold, will immediately cause the GATE pin to be pulled

low. The GATE pin will remain low until the voltage on this pin falls below the low threshold limit,

initiating a new start-up cycle.

3

UV

This Under Voltage sense pin, when below its low threshold limit will ensure that the GATE pin

is low. The GATE pin will remain low until the voltage on this pin rises above the high threshold,

initializing a new start-up cycle.

4

VEE

This pin is the negative voltage power supply input to the circuit.

5

VDD

This pin is the positive voltage power supply input to the circuit.

6

RAMP

This pin provides a current output so that a timing ramp voltage is generated when a capacitor is

connected. The initial portion of the ramp provides a time delay, which in conjunction with the Un-

der Voltage detection circuit eliminates circuit card insertion contact bounce. The RAMP pin also

controls the delay between the current limit mode disengaging and the PWRGD signal activating;

as well as the current rise profile after the initial turn on delay.

7

GATE

This is the GATE driver output for the external N-Channel MOSFET.

8

SENSE

The current sense resistor connected from this pin to VEE pin programs the current limit. Constant

current output mode is established when the voltage drop across this resistor reaches 50mV.

Pin Description