Section 1
Power

1.1 External Power Supply Requirements

This section sets out the power supply requirements for the motherboard. They are achievable with low-cost PC power supplies.

Table 1. External Power Supply Requirements
Output

Tolerance

Max Ripple

 Note
+5v

+5%

-4%

50 mv P-P

The combined 3.3v and 5.0v power cannot exceed 100W on standard 200W supplies. If more power or current is required, larger supplies can be used.

+12v

+5%

-5%

120 mv P-P

-12v

+10%

-9%

120 mv P-P

-5v

+10%

-10%

120 mv P-P

Not used on the motherboard. Routed from the power supply connector to the ISA slots on the PCI/ISA riser card.

+3.3v

+5%

-4%

50 mv P-P

See +5v supply note

1.1.1 Power Supply Current Requirements

Table 2 shows the approximate current capacities of the motherboard and of a typical standard 200W PC power supply.

Table 2. Approximate Current Capacities and Requirements (Amps)
Row

 Element

3.3v (2)

+5v (2)

+12v

-12v

-5v (1)

1

Standard 200W power supply total capacity

20.0

20.0

8.0

0.5

0.5

2

Motherboard power connectors capacity

20.0

20.0

5.0

5.0

0.5

3

Maximum current that the 200W power supply can deliver to the motherboard connectors.

20.0

12.6
(4)

3.0
(4)

0.5
(5)

0.5

4

Current requirements of motherboard with two 8M SIMMs, 512K synchronous L2 cache, riser, key board, and mouse, running typical code. 66MHz CPU bus. 33MHz PCI bus.

2.8

4

0.1

0.02

0

5

Budgeted Current Requirement for CPU Slot 1

7.5

2.5

0.01

0

0

6

Budgeted Current Requirement for CPU Slot 2

7.5

2.5

0.01

0

0

7

Cheetah3 Current Requirements
(66MHz bus & 132MHz 604).

5.6

0

0

0

0

8

Total available current for add-in memory, PCI/ISA cards, and peripherals with 200W supply.
Row8 = Row1 - Row4 - Row5 - Row6

2.8 (3)

11

7.8

0.48

0.5

9

Total available current for add-in memory, PCI/ISA cards, and peripherals with 200W supply.
Row9 = Row1 - Row4 - 2*Row7

6.0 (3)

11

7.8

0.48

0.5

10

Maximum available current for PCI/ISA cards thru motherboard.
Row10 = Row3 - Row4 - Row5 - Row6

2.8 (3)

3.6

2.8

0.48

0.5

11

Maximum available current for PCI/ISA cards thru motherboard.
Row11 = Row3 - Row4 - 2*Row7

6.0 (3)

3.6

2.8

0.48

0.5

Notes:

  1. The -5v is not used on the motherboard, but it is routed from the power supply connector to the ISA slots.
  2. The combined 3.3v and 5.0v power cannot exceed 100W on standard 200W supplies. If more power is required larger supplies can be used.
  3. The 3.3v current for the PCI slots on the riser card is provided via a 6 pin connector on the motherboard (J50) and is connected to riser card connector J7 via a 6 conductor cable capable of carrying 9 amps.
  4. Limited by the number and current capacity of the power supply connectors that can be plugged into the motherboard.
  5. Limited by the capacity of the power supply.

1.1.2 Power Supply Power Requirements

Table 3 shows the approximate power capacities of the motherboard and of a typical standard 200W PC power supply.

Table 3. Approximate Power Capacities and Requirements (Watts)
Row

 Element

+5v/3.3v

12v

-12v

-5v

Total

1

Standard 200W power supply total capacity

100

96

6.0

2.5

200

2

Base motherboard with two 8M SIMMs, 512K syn chronous L2 cache, riser, keyboard, and mouse, running typical code. 66MHz CPU bus & 33MHz PCI bus.

31

1.2

0.24

0

32.5

3

Budgeted Power Requirements for CPU Slot 1

25

0.12

0

0

25

4

Budgeted Power Requirements for CPU Slot 2

25

0.12

0

0

25

5

Cheetah3 Power Requirements
(66MHz bus & 132MHz 604)

15

0

0

0

15

6

Total available power for add-in memory, PCI/ISA cards, and peripherals with 200W supply.
Row6 = Row1 - Row2 - Row3 - Row4

19

94.8

5.75

2.5

117

7

Total available power for add-in memory, PCI/ISA cards, and peripherals with 200W supply.
Row7 = Row1 - Row2 - 2*Row5

39

96

5.75

2.5

137

1.1.3 Additional Power Supply Requirements

  1. Overshoot on any voltage must be less than 10% of nominal and must decay to within the regulation band within 50 msec.
  2. In any failure situation, the power supply must shut down before the +5v output reaches 6.5v, to give the motherboard a reasonable chance of surviving; however, damage may occur at any voltage above 5.5v.
  3. Power_Good signal requirements:
S The signal must be at a TTL down level when power is applied until >100 msec to 500 msec after the 5v supply has reached its minimum regulation level, and at TTL high level thereafter, as long as outputs are within regulation.

S At turn-off, the Power Good signal must drop to a TTL low level before any output drops below its regulation limits.

S The driver must be capable of driving 400 microamps or sinking 5 milliamps. The rise time/fall time must be less than 1 usec, 10--90%

  1. The +5v rise time (10%-90%) shall be 3 msec to 100 msec with a maximum slope of 0.75 volts/msec for voltages above 1.5 volts for all loadings.
  2. All supply voltages shall track within 50 msec of each other measured at the 50% point.

1.2 Onboard 3.6v Regulator

There is a 3.6 volt regulator on the reference design to support CPU cards with 3.6v devices. The input for this device is supplied by the +5v regulator.

Table 4. Specifications for 3.6v Regulator on the Motherboard

Specification

Value

Output Voltage

3.6v  3%

Output Current

0.01 A to 2 A

Input voltage

4.75v to 5.25v

Pass element maximum case temperature

110 5C

Tracking

In regulation <1ms after +5 reaches 4.75v.

Overcurrent

No current limit feature