LTC4216IDE datasheet(19/24 Pages) LINER

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LTC4216

4216f

Figure 13. Connecting Transient Protection

Devices to the LTC4216’s Load Supply Rail

the plug-in boards, the LTC4216 provides two separate

pins for bias supply input and load supply sensing. With

this conﬁguration, an RC network, RY and CY, shown in

Figure 13, can be used with the VCC pin to ride out supply

glitches during output-shorts or adjacent board shorts.

The RC network shown has a time constant of 7µs and

this is good enough for the supply to ride out most supply

glitches, preventing the device from entering an under-

voltage lockout condition unnecessarily or losing supply

temporarily. When VCC and SENSEP pins are connected

together, the RY value should be chosen such that VCC pin

voltage is lower than SENSEP by 70mV; otherwise, part of

VCC pin current will be diverted through SENSEP pin.

This unique scheme of separating the device’s supply input

and sensing also provides the ﬂexibility of operating the

load supply from ground to its supply rail with a minimum

bias supply voltage of 2.3V. For proper operation, the load

supply is required to be equal to or less than the bias sup-

ply voltage (maximum 6V).

Supply Transients Protection

There are two methods used in most applications to

eliminate supply transients:

1. Transient voltage suppressor to clip the transient to

a safe level.

2. Snubber (series RC) network.

For applications with load supply voltages of 3.3V or

higher, the ringing and overshoot during hot-swap-

ping or output-shorts can easily exceed the absolute

maximum rating of the LTC4216. To minimize the risk,

a transient voltage suppressor and snubber network

are highly recommended at the SENSEP pin. For ap-

plications with load supply voltages of 2.5V or below,

usually a snubber network is adequate to reduce the

supply ringing.

Figure 13 shows the connections of the supply tran-

sient protection devices, Z1, RX and CX, around the

LTC4216. The RC network, RY and CY, at the VCC pin

also serve as a snubber circuit for the load supply (VIN).

On the PCB layout, these transient protection devices

should be mounted very close to the LTC4216’s load

supply rail using short lead lengths to minimize lead

inductance.

SENSEP SENSEN GATE

VCC

GND

FILTER

TIMER

LTC4216**

0.33

µF

0.1

µF

Z1: SMAJ6.0A

**ADDITIONAL DETAILS

OMITTED FOR CLARITY

VOUT

CLOAD

RSENSE

Ω

4216 F13

VIN

APPLICATIO S I FOR ATIO

Staggered Pins Connections

The LTC4216 can be used on either the backplane side of

the connector or a printed circuit board, and examples for

both are shown in Figure 14 and 15. Printed circuit board

edge connectors with staggered pins are recommended as

the insertion and removal of circuit boards will sequence

the pin connections. Supplies (VCC and SENSEP) and

ground connections on the printed circuit board should

be wired to the long pins or blades of the edge connector.

Control signal (ON) and status signals (⎯R⎯E⎯S⎯E⎯T and ⎯F⎯A⎯U⎯L⎯T)

passing through the edge connector should be wired to

short pins or blades.

Backplane and PCB Connection Sensing

The LTC4216’s ON pin can be used in various ways to

detect whether the printed circuit board is seated properly

in the backplane connector before the LTC4216 begins a

start-up cycle.

An example is shown in Figure 14, in which the LTC4216

is mounted on the PCB and the R1/R2 resistive divider

is connected to the ON pin. On the edge connector, R2

is wired to a short pin. Before the connectors are mated,

the ON pin is held low by R1, keeping the LTC4216 in an

off state. When the connectors are mated, the resistive

divider is connected to the load supply (VIN) and the ON

pin voltage rises above 0.8V, turning the LTC4216 on.

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