DATASHEET

DS_DIM3R3_09102010

9

FEATURES AND DESIGN

CONSIDERATIONS

Introduction

The DIM3R3/050 module is designed to simplify the task

and reduce the board space of an ATCA (Advanced

Telecommunications Computing Architecture) power

entry distribution requirements in the system board.

The main functionality of the module is to provide dual,

redundant -

48V A/B Feed OR’ing, inrush protection for

hot swap capability, EMI filtering to attenuate the noise

generated by the downstream DC/DC converters, and a

72V output voltage for charging the holdup capacitor.

The module also has a management power supply

which provides an 8W, 3.3V management power and/or

a 5V/100mA output (optional) to power the blue LED per

PICMG 3.0 requirement.

The module provides A/B feed/fuse open alarm, over

current protection, over voltage protection, and over

temperature protection. It also provides input under

voltage lock-out and input reverse polarity protection.

A/B Feed OR’ing

To improve the total power distribution efficiency, four

internal MOSFETs are used to function as the OR

’ing

diodes. A control circuit is designed to keep about

100mV voltage drop across MOSFET. During full load

operation, the MOSFETs are fully turned on. During light

load, the MOSFETs work under a high Rdson condition.

If the output current decreases to zero, the MOSFETs

will be turned off. This design provides module a reverse

voltage sustain function. The module shall not be

damaged from reverse polarity connection in the event

of mis-wiring of either input feeds at the shelf input

terminals. Furthermore, a fast shut down circuit is

designed for the negative current case. This design

protects the common DC bus against hard short faults at

the sourcing power supply output.

Hot Swap Functionality

The hot-swap function is designed to limit the inrush

current charged to the bulk capacitor of the down stream

bus converter. The current value and duration comply

with the PICMG 3.0’s Inrush Transient specs.

Although the inrush current for bulk capacitor is under

control, special attentions need to be paid to the current

for EMI filter because this circuit is in front of hot-swap

circuit.

EMI Filtering

An internal EMI filter is designed for the ATCA board to

meet the system conducted emission requirements of

CISPR 22 Class B when used with Delta DC/DC

converters.

Figure 17 shows the EMI performance of DIM3R3 when

it worked with Delta power module Q48SH12025NRFA

(36~75Vin, 12V/25A output Quarter brick). It meets

CISPR 22 Class B requirement.

Figure 11: EMI test result with Q48SH12025NRFA:

Holdup

Capacitor

Charging

Current

(72V_CAP)

An off line holdup capacitor (C_HLDP) is needed to

store energy for the holdup time requirement. C_HLDP

is charged to 72V (+/- 3% tolerance). For a fixed energy

storage requirement, high capacitor voltage reduces

capacitor capacitance and size. A constant current

circuit charges C_HLDP before its voltage reaches the

high limitation and isolates it from power train circuit.

The discharge switch will turn on if both A&B feeds have

dropped

below

–38V (typical). C_HLDP will be

connected to power train and provided the energy for

system operation.

C_HLDP is calculated by the following equation:

2

2

72

_

*

*

2

_

Vth

V

HLDP

T

Power

HLDP

C





Where Power is the input power to the downstream

DC/DC

converter;

T_HLDP

is

the

holdup

time

requirement; Vth is the minimum input voltage threshold

of the downstream DC/DC converter.