Detailed Description

The MAX5946L EV kit demonstrates a PCI Express-16

dual hot-plug circuit design. Two PCI Express-16 chan-

nels are provided to evaluate a PCI Express-16 card.

The EV kit uses a latching MAX5946L hot-plug controller

in a 36-pin thin QFN package to control both A and B

channels’ output power and monitor for faults.

The MAX5946L IC independently controls each chan-

nel’s output power. External n-channel MOSFETs are

used to control power to the 12V and 3.3V outputs of

each channel. Current-sensing resistors (R1–R4) are

used for the 12V and 3.3V outputs of each channel.

Internal MOSFETs on the MAX5946L control the 3.3V

auxiliary outputs of each channel.

If an overcurrent fault persists on either channel, the

MAX5946L will shut down the respective channel. The

fault is reported at the respective channel’s open-drain

power-good pin (PWRGDA, PWRGDB) and fault pin

(FAULTA, FAULTB). The MAX5946L power-on reset

(POR) is configured for 160ms; however, the POR can

be reconfigured after installing resistor R27.

Slide switches are provided to independently enable/dis-

able each channel’s main output (SW3, SW5) and auxil-

iary (SW4, SW6) 3.3V output when the SMBus control is

not used. Jumpers JU1 and JU2 can be used to provide

a presence-detect function for the respective channel if

PCI Express cards are not used. Momentary pushbutton

switches SW1 and SW2 are provided to demonstrate the

MAX5946L de-bounced logic gate outputs.

The MAX5946L EV kit features green LEDs connected

to each channel’s 12V, 3.3V, and 3.3V auxiliary outputs

that indicate if the respective output is currently pow-

ered. Red test points for the 12V and 3.3V outputs, vari-

ous PCI Express signals, and other circuit signals such

as the gate drive of each MOSFET have been provided

for probing on the EV kit board. All of the EV kit’s black

test points are GND points.

The EV kit also features PC board pads for installing

external resistors and capacitors near each MOSFET

gate terminal to increase the MOSFET’s gate turn-on

time. Surface-mount 0805 case size components can

the MOSFET’s gate R and C designators.

The EV kit can be reconfigured for evaluating an x1, x4,

or x8 PCI Express dual hot-plug design by replacing

the appropriate current-sense resistor, R1 or R2.

Consult the appropriate PCI Express specification or

Table 1 in the MAX5946 IC data sheet for selecting

other designs. PC board pads are provided to demon-

strate the MAX5946L hot-plug features without using

the PCI Express-16 connectors.

For evaluating external DC loads, the cables connect-

ing the 12V and 3.3V outputs to the external DC load

must be rated for at least 10A and be shorter than 12in.

Additionally, current-sense resistors R1–R4 are config-

ured for the maximum allowable output current on the

12V and 3.3V outputs. These resistors should only be

reconfigured for lower output currents.

The MAX5946L EV kit features a MAX7313 16-port I/O

expander (U2) and PC board pads for interfacing to a

user’s SMBus system. Resistors R19–R24 configure the

MAX7313 SMBus serial address. The MAX7313 can be

used to enable/disable each channel’s main output and

auxiliary 3.3V output independently. See the MAX7313

Input/Output Expander and SMBus Interface section in

this document for more details.

Jumper and Switch Selection

Several jumper and switch selections in Tables 1–6 dis-

play the functions provided by the MAX5946L EV kit.

Presence Detect Channels A and B

The MAX5946L EV kit features two jumpers that can

simulate a PCI Express-16 card being plugged into a

connector. Jumpers JU1 and/or JU2 are used to pro-

vide a presence-detect function for the respective A or

B channel. An external load (resistive and capacitive)

must be connected to the channel’s output PC board

pads simulating a real PCI Express card. Table 1 lists

the various jumper options.

When using a real PCI Express card, these jumper

shunts must be removed so that the card has control of

the presence detection.

MAX5946L Evaluation Kit/Evaluation System

4

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Table 1. Channel A and B Presence-Detection Functions

JUMPER

SHUNT

MAX5946L PIN CONNECTION

EV KIT OPERATION SIMULATED

JU1

Installed

PRES-DETA pin pulled low

PCI Express card inserted in channel A

JU1

None*

PRES-DETA pin pulled high

No PCI Express card in channel A

JU2

Installed

PRES-DETB pin pulled low

PCI Express card inserted in channel B

JU2

None*

PRES-DETB pin pulled high

No PCI Express card in channel B

*When using a real PCI Express card, these jumper shunts must be removed so that the card has control of the presence detection.