HIP6500BCB datasheet(13/30 Pages) RENESAS

13 / 30 page

HIP6500B

FN4870 Rev 0.00

Page 13 of 15

May 2000

Select a package and heatsink that maintains the junction

temperature below the rating with the maximum expected

ambient temperature.

The active element on the 2.5V/3.3VMEM output has

different requirements for each of the two voltage settings. In

2.5V systems utilizing RDRAM (or voltage-compatible)

memory, Q1 has to be a bipolar NPN capable of conducting

up to 7.5A and exhibit a current gain (hfe) of minimum 40 at

this current and 0.7V VCE; in such systems the 2.5V output

is actively regulated while in active state. In 3.3V systems

(SDRAM or compatible) Q1 has to be an N-Channel

MOSFET; in such systems the MOSFET is switched on

during active state (S0, S1). The main criteria for the

selection of this transistor 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

The gate bias available for this MOSFET is of the order of 8V.

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

of the ATX supply into the 5VDUAL output during S3 and S5

states (as dictated by EN5VDL status), then, similar to the

situation where Q1 is a MOSFET, the selection criteria of

this device is also proper voltage budgeting. The maximum

rDS(ON), however, has to be achieved with only 4.5V of

VGS, 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).

Q3, Q4

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

and 5V inputs provided by the ATX supply into the

3.3VDUAL and 5VDUAL outputs, respectively, while in

active (S0, S1) state. Similar rDS(ON) criteria apply in these

cases as well. Unlike the PMOS, however, these NMOS

transistors get the benefit of an increased VGS drive

(approximately 8V and 7V, respectively).

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

on the 3.3VDUAL output has to have a minimum current gain

of 100 at 1.5V VCE and 500mA ICE throughout the in-circuit

operating temperature range.

rDS ON

max

VINmin VOUTmin

–

IOUTmax

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