ISL6504 datasheet(13/17 Pages) RENESAS

13 / 17 page

ISL6504, ISL6504A

FN9062 Rev 2.00

Page 13 of 17

Apr 13, 2004

The NPN transistor used as sleep state pass element on the

3.3VDUAL output has to have a minimum current gain of 100 at

1.5V VCE and 650mA ICE throughout the in-circuit operating

temperature range. For larger current ratings on the 3.3VDUAL

output (providing the ATX 5VSB output rating is equally

extended), selection criteria for Q1 include an appropriate

current gain (hfe) and saturation characteristics.

Q2, Q4

These N-Channel MOSFETs are used to switch the 3.3V and

5V inputs provided by the ATX supply into the

3.3VDUAL/3.3VSB and 5VDUAL outputs while in active (S0, S1)

state. The main criteria for the selection of these transistors is

output voltage budgeting. The maximum rDS(ON) allowed at

highest junction temperature can be expressed with the

following equation:

, where

VINmin - minimum input voltage

VOUTmin - minimum output voltage allowed

IOUTmax - maximum output current

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

the ATX supply into the 5VDUAL output during sleep states,

then the selection criteria of this device is proper voltage

budgeting. The maximum rDS(ON), however, has to be

achieved with only 4.5V of gate-to-source voltage, so a logic

level MOSFET needs to be selected. 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).

rDS ON

max

VINmin VOUTmin

–

IOUTmax

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ISL6504 Datasheet(PDF) 13 Page - Renesas Technology Corp