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LTC4216I

Ultralow Voltage Hot Swap Controller

Linear Technology 

LTC4216

Applications Information

Hot Circuit Insertion

When circuit boards are inserted into a live backplane, the

supply bypass capacitors can draw huge transient current

from the power bus as they charge. Potentially, the flow

of current could damage the connector pins and glitch

the power bus, causing other boards in the system to

reset. The LTC4216 is designed to turn on or off a circuit

board supply in a controlled manner, allowing insertion

or removal without glitches or connector damage.

Overview of LTC4216 Features

1. Allows safe board insertion and removal from a live

backplane.

2. Controls load voltages from 0V to 6V.

3. High side gate drive for external N-channel MOSFET.

4. Adjustable soft-start with inrush current limiting for

large load capacitor during start-up.

5. Adjustable analog current limit (ACL) with circuit

breaker fault time-out during an overcurrent fault condi-

tion. No external gate capacitor is required for the ACL

loop compensation.

6. Electronic circuit breaker tripping at 25mV across the

sense resistor. The response time is adjustable through

an external capacitor at the FILTER pin.

7. Provides an ON pin to turn on and off the device. This can

also be used to reset the device after a circuit breaker trip.

8. Provides output supply voltage monitoring through the

FB pin and signals the RESET pin output.

9. Provides fault status output.

ON Control

The ON pin has two hysteretic comparators with differ-

ent threshold levels (0.8V and 0.4V) and they serve two

purposes:

1. Turn on the device if the ON pin voltage > 0.8V for more

than 6µs and turn it off if the ON pin voltage < 0.72V for

more than 15µs.

2. Reset the device if the ON pin voltage < 0.4V for more

than 30µs after a circuit breaker trip.

There are various methods of setting the ON pin

voltage:

1. Tie the ON pin to the load supply (VIN) through a 10k

pull-up resistor.

2. Drive the ON pin with an ON/OFF logic signal from the

system controller.

3. Connect an external resistive divider at the ON pin.

This divider can be used to set a higher value for the load

supply undervoltage lockout voltage than the internal VCC

undervoltage lockout circuit.

For example, as shown in Figure 17, if both VCC and

SENSEP pins are connected to a 5V load supply, choosing

the resistive divider values, R1 = 20k, R2 = 80.6k, turns on

the device when the load supply voltage reaches around

80% of its final value.

VCC Undervoltage Lockout

A hysteretic comparator, UVLO, monitors bias supply (VCC)

for undervoltage. The thresholds are defined by VCC(UVL)

(2.12V) and its hysteresis, ΔVCC(UVL,HYST) (120mV). When

VCC rises above VCC(UVL), the device is enabled. When

VCC falls below (VCC(UVL) – ΔVCC(UVL,HYST)), the device is

disabled and GATE is pulled low. If VCC cycles below this

threshold for more than 200µs, following a circuit breaker

trip, it clears the fault latch. Any bias supply glitches that

last less than 10µs will be rejected by the UVLO glitch filter.

Timer

An external capacitor, C1, is used at TIMER pin to provide

two timing cycles for the LTC4216. The first timing cycle

is the debounce cycle when the ON pin is first turned on,

both the GATE and SS pins are held low and any short-

circuit faults are ignored by the electronic circuit breaker.

Second timing cycle is the power-good delay before the

RESET pin goes high when the FB pin voltage exceeds

0.6V and its hysteresis.

The TIMER pin sources 2µA into C1 during the two timing

cycles and is then pulled low by an internal N-channel

For more information www.linear.com/LTC4216

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