7

FN4855.3

July 13, 2005

Over-Current Protection

The over-current function protects the converter from a

shorted output by using the upper MOSFET’s on-resistance,

converter’s efficiency and reduces cost by eliminating a

current sensing resistor.

The over-current function cycles the soft-start function in a

programs the over-current trip level. An internal 200

μA current

over-current function initiates a soft-start sequence. The soft-

inhibits PWM operation. The soft-start function recharges

clamped to the SS voltage. Should an overload occur while

shows this operation with an overload condition. Note that the

charging interval and causes an over-current trip. The

converter dissipates very little power with this method. The

measured input power for the conditions of Figure 4 is 2.5W.

The over-current function will trip at a peak inductor current

typical). The OC trip point varies mainly due to the

resistor from the equation above with:

temperature.

,

where

ΔI is the output inductor ripple current.

For an equation for the ripple current see the section under

component guidelines titled ‘Output Inductor Selection’.

A small ceramic capacitor should be placed in parallel with

presence of switching noise on the input voltage.

Output Voltage Program

The output voltage of a HIP6004D converter is programmed

voltage identification (VID) pins program an internal voltage

reference (DACOUT) with a TTL-compatible 5-bit digital-to-

analog converter (DAC). The level of DACOUT also sets the

PGOOD and OVP thresholds. Table 1 specifies the DACOUT

voltage for the 32 different combinations of connections on the

VID pins. The output voltage should not be adjusted while the

converter is delivering power. Remove input power before

changing the output voltage. Adjusting the output voltage

during operation could toggle the PGOOD signal and exercise

the overvoltage protection.

‘11111’ VID pin combination resulting in a 0V output setting

activates the Power-On Reset function and disables the gate

drives circuitry. For this specific VID combination, though,

PGOOD asserts a high level. This unusual behavior has been

implemented in order to allow for operation in dual-

microprocessor systems where AND-ing of the PGOOD signals

from two individual power converters is implemented.

Application Guidelines

Layout Considerations

As in any high frequency switching converter, layout is very

important. Switching current from one power device to another

can generate voltage transients across the impedances of the

interconnecting bond wires and circuit traces. These

interconnecting impedances should be minimized by using

wide, short printed circuit traces. The critical components

should be located as close together as possible, using ground

plane construction or single point grounding.

0A

0V

TIME (20ms/DIV)

5A

10A

15A

2V

4V

FIGURE 4. OVER-CURRENT OPERATION

()

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

=

()

ΔI

() 2

⁄

+

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HIP6004D