A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 22

• Manufacturer Part Number: A8514KLPTR-T
• Description: IC LED DVR WHT 4X80MA 16-ETSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8514KLPTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8514
Input overcurrent protection and disconnect switch
The primary function of the input disconnect switch is to protect
the system and the device from catastrophic input currents during
a fault condition. The external circuit implementing the discon-
nect is shown in figure 29. If the input disconnect switch is not
used, the VSENSE pin must be tied to VIN and the GATE pin
must be left open.
When selecting the external PMOS, check for the following
parameters:
The input disconnect switch has two modes of operation:
• 1X mode
the preset current limit value, the disconnect switch enters a con-
stant-current mode for a maximum duration of 10,000 cycles or
5 ms at 2 MHz. During this time, the Fault flag is set immediately
and the disconnect switch goes into a linear mode of operation,
in which the input current will be limited to a value approximate
to the 1X current trip point level (figure 30). If the fault corrects
itself before the expiration of the timer, the Fault flag will be
removed and normal operation will resume.
The user can also during this time decide whether to shut down
the A8514. To immediately shut down the device, pull the FSET/
SYNC pin low for more than 7 μs. After the FSET/SYNC pin has
been low for a period longer than 7 μs, the IC will stop switching,
the input disconnect switch will open, and the LEDx pins will
stop sinking current. The A8514 can be powered-down into low
power mode. To do so, disable the IC by keeping the PWM/EN
pin low for a period of 32,750 clock cycles. To keep the discon-
nect switch stable while the disconnect switch is in 1X mode, use
a 22 nF capacitor for C
Figure 29. Typical circuit showing the implementation of the input
disconnect feature.
• Drain-source breakdown voltage V
• Gate threshold voltage (make sure it is fully conducting at
• R
V
similar, not at –10 V; derate it for higher temperature
GS
DS(on)
= –4 V, and cut-off at –1 V)
: Make sure the on-resistance is rated at V
V
When the input current is between one and two times
IN
R
R
C
SC
ADJ
and a 20 Ω resistor for R
R
C
VSENSE
VIN
(BR)DSS
C
C
GATE
Q1
> –40 V
A8514
C
Wide Input Voltage Range, High Efficiency
.
GS
To L1
= –4.5 V or
Figure 30. Showing typical wave forms for a 3-A, 1X current limit under a
fault condition; shows f
div.), GATE (ch3, 5 V/div.), and PWM/EN (ch4, 5 V/div.), time = 5 ms/div.
Figure 31. 2X mode, secondary overcurrent fault condition. I
current through the switch. The Fault flag is set at the 1X current limit, and
when the 2X current limit is reached the A8514 disables the gate of the
disconnect switch (GATE); shows ¯ F ¯ ¯ A ¯ U ¯ ¯ L ¯ ¯ T ¯ (ch1, 5 V/div.), GATE (ch2,
10 V/div.), I
C1
C2
C3
C4
C1
C2
C3
C4
PWM/EN
PWM/EN
FAULT
GATE
GATE
FAULT
I
IN
I
IN
IN
(2) Disconnect switch
goes into a linear mode
Fault flag set at
(ch3, 2 A/div.), and PWM/EN (ch4, 5 V/div.), time = 5 μs/div.
1X trip point
Fault Tolerant LED Driver
(1) Initial fault
detected
SW
= 800 kHz, ¯ F ¯ ¯ A ¯ U ¯ ¯ L ¯ ¯ T ¯ (ch1, 5 V/div.), I
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
t
t
A8514 shuts down at
2X trip point
(4) After 12.5 ms,
disconnect switch
shuts down
(3) I
IN
limited to 3 A
IN
IN
is the input
(ch2, 2 A/
22