12

result a brisk transfer of energy from the input capacitors to

the supplied outputs. At the transition between active and

sleep states, this phenomena could result in the 5VSB

voltage dropping below the POR level (typically 4.1V) and

temporarily disabling the HIP6502. The solution to a

potential problem such as this is using larger input

capacitors with a lower total combined ESR.

Transistor Selection/Considerations

The HIP6502 usually requires one P-Channel (or bipolar

PNP), three N-Channel MOSFETs and two bipolar NPN

transistors.

One important criteria for selection of transistors for all the

linear regulators/switching elements is package selection for

efficient removal of heat. The power dissipated in a linear

regulator/switching element is

Select a package and heatsink that maintains the junction

temperature below the rating with the maximum expected

ambient temperature.

Q1

bipolar NPN capable of conducting the maximum active

Q2

The NPN transistor used as sleep state pass element (Q2)

operating temperature range.

Q3, 4, 6

The three N-Channel MOSFETs are used to switch the 3.3V

S1) state. The main criteria for the selection of these

transistors is output voltage budgeting. The maximum

expressed with the following equation:

, where

The gate bias available for these MOSFETs is of the order of

8V.

Q5

If a P-Channel MOSFET is used to switch the 5VSB output

states (as dictated by EN5VDL status), then the selection

criteria of this device is proper voltage budgeting. The

If a PNP device is chosen to perform this function, it has to

have a low saturation voltage while providing the maximum

sleep current and have a current gain sufficiently high to be

saturated using the minimum drive current (typically 20mA).

P

LINEAR

I

O

V

IN

V

OUT

–

()

×

=

r

DS ON

()max

V

INmin

V

OUTmin

–

I

OUTmax

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

=

HIP6502