A8514KLPTR-T Просмотр технического описания (PDF) - Allegro MicroSystems

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A8514KLPTR-T

Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver

Allegro MicroSystems 

A8514

Wide Input Voltage Range, High Efficiency

Fault Tolerant LED Driver

internal fault registers. As an example, at a 2 MHz clock fre-

quency, it will take approximately 16.3 ms to shut down the IC

into the low power mode (figure 33). When the A8514 is shut

down, the IC will disable all current sources and wait until the

PWM/EN signal goes high to re-enable the IC. If faster shut

down is required, the FSET/SYNC pin can be used.

Fault protection during operation

The A8514 constantly monitors the state of the system to deter-

mine if any fault conditions occur during normal operation. The

response to a triggered fault condition is summarized in the Fault

Mode table.

The possible fault conditions that the device can detect are: Open

LED pin, LED pin shorted to ground, shorted inductor, VOUT

short to ground, SW pin shorted to ground, ISET pin shorted to

ground, and input disconnect switch source shorted to ground.

Note the following:

• Some of the protection features might not be active during

startup, to prevent false triggering of fault conditions.

• Some of these faults will not be protected if the input disconnect

switch is not being used. An example of this is VOUT short to

ground.

Fault Mode Table

Fault Name

Type

Primary switch

overcurrent protection

(cycle-by-cycle

current limit)

Auto-restart

Secondary switch

current limit

Latched

Input disconnect

current limit

Latched

Secondary OVP

Latched

Active

Always

Always

Always

Always

Fault

Flag

Set

Description

Boost

Disconnect

switch

Sink

driver

No

This fault condition is triggered by the cycle-by-

cycle current limit, ISW(LIM).

Off for

a single

cycle

On

On

When the current through the boost switch exceeds

secondary current SW limit (ISW(LIM2)) the device

Yes

immediately shuts down the disconnect switch,

LED drivers, and boost. The Fault flag is set. To re-

Off

Off

Off

enable the device, the PWM/EN pin must be pulled

low for 32,750 clock cycles.

The device is immediately shut off if the voltage

across the input sense resistor is 2X the preset

current value. The Fault flag is set. If the input

Yes

current limit is between 1X and 2X, the Fault flag

is set but the IC will continue to operate normally

Off

Off

Off

for tGFAULT1 or until it is shut down. To re-enable

the device the PWM/EN pin must be pulled low for

32,750 clock cycles.

Secondary overvoltage protection is used for open

diode detection. When diode D1 opens, the SW pin

voltage will increase until VOVP(SEC) is reached. This

Yes fault latches the IC. The input disconnect switch is

Off

Off

Off

disabled as well as the LED drivers, and the Fault

flag is set. To re-enable the part the PWM pin must

be pulled low for 32,750 clock cycles.

Continued on the next page…

Allegro MicroSystems, Inc.

24

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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