LM5064PMHSLASHNOPB datasheet(27/64 Pages) TI2

27 / 64 page

Load

VCC

GND

BACKPLANE

OUT

LIVE

GATE

SENSE

VEE

VSYS

LM 5064

- 48V

PLUG- IN BOARD

LM5064

www.ti.com

SNVS718E – JUNE 2011 – REVISED FEBRUARY 2013

SYSTEM CONSIDERATIONS

Continued proper operation of the LM5064 hot swap circuit requires a voltage clamping element present on the

supply side of the connector into which the hot swap circuit is plugged in. A TVS (Transient Voltage Suppressor)

is ideal, as depicted in Figure 15 as Z1. The TVS is necessary to absorb the voltage transient generated

whenever the hot swap circuit shuts off the load current. If the TVS is not present, inductance in the supply lines

will generate a voltage transient at shutdown which can exceed the absolute maximum rating of the LM5064,

resulting in its destruction. For low current solutions (<2A), a capacitor may be sufficient to limit the voltage

surge, however this comes at the expense of input surge current on card insertion.

If the load powered by the LM5064 hot swap circuit has inductive characteristics, a Schottky diode (D1) is

required across the LM5064’s output, along with some load capacitance (CL). The capacitance and the diode are

necessary to limit the negative excursion at the OUT pin when the load current is shut off. If the OUT pin

transitions more than 0.3V negative the LM5064 can be permanently damaged. See Figure 15.

Figure 15. Output Diode Required for Inductive Loads

System Considerations During Surge Events

The control MOSFET, Q1, has a body-diode, illustrated in Figure 16, where current can freely flow in the reverse

direction. The most common cause of a reverse current is a discharge event at the input of the hot-swap circuit

when the output capacitance discharges to the input. Normally, reverse current flow presents no issue for hot-

swap devices during events such as shutdown and minor input power perturbations. However, extreme situations

such as high energy lighting surge line disturbances can expose the hot-swap circuit to pulses of ultra fast - high

amplitude reverse currents. It is common to observe current amplitudes on the order of 1000A in these situations.

Figure 16 illustrates what an extreme input discharge event may look like and how it affects the circuit.

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LM5064PMH/NOPB Datasheet(PDF) 27 Page - Texas Instruments