11

FN6901.0

April 27, 2009

GPIO1/REFIN

This is a dual function pin. If VMSET/MODE is not connected

to VCC5 then this pin serves as GPIO1. Refer to Table 3 for

GPIO commands interpretation.

If VMSET/MODE is connected to VCC5 then this pin will

serve as REFIN. As REFIN, this pin is the non-inverting input

to the error amplifier. Connect the desired reference voltage

to this pin in the range of 0.6V to 1.25V.

Connect this pin to VCC5 to use internal reference.

REFOUT

It provides buffered reference output for REFIN. Connect

2.2µF decoupling capacitor to this pin.

VMSET/MODE

This pin is a dual function pin. Tie this pin to VCC5 to disable

voltage margining. When not tied to VCC5, this pin serves as

VMSET. Connect a resistor from this pin to ground to set

delta for voltage margining. If voltage margining and external

reference tracking mode are not needed, this pin can be tied

directly to ground.

GPIO2

This is general purpose IO pin for voltage margining. Refer

to Table 3.

Exposed Thermal Pad

This pad is electrically isolated. Connect this pad to the

signal ground plane using at least five vias for a robust

thermal conduction path.

Functional Description

Initialization

The ISL6420B automatically initializes upon receipt of power.

The Power-On Reset (POR) function monitors the internal bias

voltage generated from LDO output (VCC5) and the ENSS pin.

The POR function initiates the soft-start operation after the

VCC5 exceeds the POR threshold. The POR function inhibits

operation with the chip disabled (ENSS pin <1V).

The device can operate from an input supply voltage of 5.6V

to 28V connected directly to the VIN pin using the internal 5V

linear regulator to bias the chip and supply the gate drivers.

For 5V ±10% applications, connect VIN to VCC5 to bypass

the linear regulator.

Soft-Start/Enable

The ISL6420B soft-start function uses an internal current

source and an external capacitor to reduce stresses and

surge current during start-up.

When the output of the internal linear regulator reaches the

POR threshold, the POR function initiates the soft-start

sequence. An internal 10µA current source charges an

external capacitor on the ENSS pin linearly from 0V to 3.3V.

When the ENSS pin voltage reaches 1V typically, the

internal 0.6V reference begins to charge following the dv/dt

of the ENSS voltage. As the soft-start pin charges from 1V to

1.6V, the reference voltage charges from 0V to 0.6V.

Figure 9 shows a typical soft-start sequence.

TABLE 2. VOLTAGE MARGINING/DDR OR TRACKING SUPPLY PIN CONFIGURATION

FUNCTION/MODES

PIN CONFIGURATIONS

VMSET/MODE

REFOUT

GPIO1/REFIN

(Note 9)

GPIO2

(Note 9)

Enable Voltage Margining

Pin Connected to GND

with resistor. It is used

as VMSET.

Connect a 2.2µF capacitor

for bypass of external

reference.

Serves as a general

purpose I/O. Refer to

Table 3.

Serves as a general

purpose I/O. Refer to

Table 3.

No Voltage Margining. Normal operation

with internal reference. Buffered

H

Connect a 2.2µF capacitor

to GND.

H (Note 10)

L

No Voltage Margining. External

H

Connect a 2.2µF capacitor

to GND.

Connect to an external

reference voltage source

(0.6V to 1.25V)

L

NOTES:

9. The GPIO1/REFIN and GPIO2 pins cannot be left floating.

10. Ensure that GPIO1/REFIN is tied high prior to the logic change at VMSET/MODE.

TABLE 3. VOLTAGE MARGINING CONTROLLED BY GPIO1

AND GPIO2

GPIO1

GPIO2

VOUT

L

L

No Change

LH

+

ΔVOUT

HL

-

ΔVOUT

H

H

Ignored

ISL6420B