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MAX5913AEMHT

+48V Quad Hot-Swap Controllers For Power-Over-LAN

Maxim Integrated 

+48V Quad Hot-Swap Controllers For

Power-Over-LAN

Detailed Description

The MAX5913A/MAX5914A quadruple hot-swap con-

trollers provide Power-Over-MDI, also known as Power-

Over-LAN systems (Figure 5). The MAX5913A/

MAX5914A enable control of four external n-channel

MOSFET switches from a single VCC ranging from

+35V to +72V, with timing control and current-limiting

functions built in.

The MAX5913A/MAX5914A features include undervolt-

age lockout (UVLO), 100mA relay drivers, dual-level cur-

rent sense, foldback current limit, programmable

overcurrent time and auto-retry periods, internal charge

pumps to drive external MOSFET and soft-start, port sta-

tus output indicating power-OK (POK) or open-circuit

conditions (Figure 6).

Switch and Relay Control Inputs

The MAX5913A/MAX5914A ON_ inputs turn on the corre-

sponding MOSFET switch. Driving ON_ high turns on the

switch if the corresponding RLYON is driven high, and

VCC > VUVLO for more than 25.6ms. Driving RLYON_

high immediately turns on the corresponding relay, and

activates the 25.6ms delay after which the corresponding

ON_ input is active. Driving RLYON_ low immediately

turns off the switch and activates a 3.2ms delay, after

which the relay is turned off. These internal delays safely

allow driving ON_ and RLYON_ simultaneously. The relay

is turned on while the switch is off so that there is no volt-

age across the relay contacts. The relay is turned off

while the switch is off so that there is no current flowing

when the relay contacts are opened (see Figure 3).

Input Voltage and UVLO

The MAX5913A/MAX5914A operate from a +35V to +72V

supply voltage. VCC powers the MAX5913A/MAX5914A

analog circuitry and is monitored continuously during

startup and normal operation. The MAX5913A/MAX5914A

keep all MOSFET switches and relay drivers securely off

before VCC rises above VUVLO. The MAX5913A/

MAX5914A turn off all MOSFET switches and relay drivers

after VCC falls below VUVLO - VUVLO,H.

Startup

When the turn-on condition is met (see the Input

Voltage and UVLO and Switch and Relay Control Inputs

sections), the MAX5913A/MAX5914A slowly turn on the

external MOSFET switch by charging its gate using a

constant current source, IGATE (10µA typ). The gate

voltage slope is determined by the total gate capaci-

tance CGATE connected to this node. Since the output

voltage follows the gate voltage, thus the output rises

with a slope determined by:

∆VOUT = IGATE

∆t

CGATE

If a capacitor load is connected to the output, the total

current through the FET is:

I

=

IGATE

CL

CGATE

+

IL

where CL is the load capacitance and IL is the current

required by any load connected to the output during

the startup phase.

If the current through the FET reaches the programmed

current-limit value:

IMAX

=

VSC

RSENSE

the internal current-limit circuitry activates and regu-

lates this FET current to be a value, ILIM, that depends

on VOUT (IFLBK) (Figure 8). See the Current Sensing

and Regulation section. In this case, the maximum rate

of change of the output is determined by:

∆VOUT = ILIM − IL

∆t

CL

The formula shows the necessity for ILIM to be larger

than IL in order to allow the output voltage to rise. The

foldback function is active as long as the circuit is in

overcurrent condition. Should the overcurrent condition

persist for a period longer than the maximum time tO,

the switch is latched off and GATE_ is discharged to

ground with a 1mA pulldown current.

If auto-retry is enabled, the switch turns on again after a

waiting period, tOFF, which is determined by the pro-

grammed duty cycle.

After the startup, the internal charge pumps provide

(VCC + 9V) typical gate overdrive to fully turn on the

switch. When the switch is fully on (voltage drop across

the switch is ≤ 1.5V), and the switch is not in current

limit, the POK signal is asserted.

Current Sensing and Regulation

The MAX5913A/MAX5914A control port current with

using two voltage comparators (dual-level detection)

that sense the voltage drop across an external current-

sense resistor. Connect CSP_ to VCC and connect a

current-sense resistor between CSP_ and DRAIN_.

Kelvin sensing should be used as shown in Figure 7.

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