10

OVERVOLTAGE PROTECTION

If the ISL6219A detects output voltages above 115% of VID,

the controller will immediately commands all PWM outputs

low. This directs the Intersil drivers to turn on the lower

MOSFETs and protect the load by preventing any further

increase in output voltage. Once the output voltage falls to

the level set by the VID code, the PWM outputs enter high-

impedance mode. The Intersil drivers respond by turning off

both upper and lower MOSFETs. If the overvoltage condition

reoccurs, the ISL6219A will again command the lower

MOSFETs to turn on. The ISL6219A will continue to protect

the load in this fashion as long as the overvoltage repeats.

After detecting an overvoltage condition, the ISL6219A

terminates normal PWM operation until it is reset by one of

two methods. Either by pulling VCC below the POR falling

threshold and restoring it above the POR rising threshold or

cycling FS/EN.

Under-Voltage

The VSEN pin also detects when the CORE voltage drops

below the VID programmed under-voltage falling threshold.

This causes PGOOD to go low, but has no other effect on

operation and is not latched.

LOAD-LINE REGULATION

In applications with high transient current slew rates, the

lowest-cost solution for maintaining regulation often requires

some kind of controlled output impedance. A current

proportional to the average current of all active channels is

steered into the inverting input of the error amplifier. There is

no DC return path connected to the FB pin except for the

sense channel current, a more complete expression for

is derived from Figures 4 and 5.

ENABLE AND DISABLE

Three separate input conditions must be met before the

ISL6219A is released from shut-down mode. The PWM

outputs are held in a high-impedance state to assure the

drivers remain off during shut-down.

The internal power-on reset circuit (POR) prevents the

ISL6219A from starting before the bias voltage at VCC

reaches the POR-rising threshold as defined in Electrical

Specifications. The rising threshold is high enough to

guarantee that all parts of the ISL6219A can perform their

functions properly. There is enough hysteresis in the POR-

falling threshold to prevent nuisance tripping.

The frequency select/enable input (FS/EN) has a 1V threshold

which must be exceeded before the internal oscillator begins

running. An external enable signal should be used to control the

gate of an external MOSFET tied to the FS/EN pin, see Figure

8. This MOSFET must pull FS/EN below the 1V threshold to

disable the controller. When enabling the controller, this

10

100

1.350

10

011

1.375

10

010

1.400

10

001

1.425

10

000

1.450

01

111

1.475

01

110

1.500

01

101

1.525

01

100

1.550

01

011

1.575

01

010

1.600

01

001

1.625

01

000

1.650

00

111

1.675

00

110

1.700

00

101

1.725

00

100

1.750

00

011

1.775

00

010

1.800

00

001

1.825

00

000

1.850

TABLE 1. VOLTAGE IDENTIFICATION CODES (Continued)

VID4

VID3

VID2

VID1

VID0

VDAC

V

DROOP

I

=

(EQ. 3)

I

AVG

I

OUT

N

-------------

r

DS ON

()

R

ISEN

----------------------

=

V

DROOP

I

OUT

N

-------------

r

DS ON

()

R

ISEN

---------------------- R

FB

=

(EQ. 4)

FIGURE 8. EXTERNAL ENABLE SIGNAL CIRCUIT

EXTERNAL CIRCUIT

FS/EN

+

-

1.23V

-

+

VCC

S1

ENABLE

SIGNAL

ISL6219A