A8513 ALLEGRO [Allegro MicroSystems], A8513 Datasheet - Page 12

• Manufacturer Part Number: A8513
• Description: Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A8513
The OVP condition can become a latched fault if, during an OVP
event, the LED current is not in regulation. This typically occurs
during an open LED string situation. If both faults occur simul-
taneously the IC will shut down and the fault flag will be set (see
figures 9, 10, and 11).
Undervoltage Protection
output undervoltage protection (UVP) against V
GND. When the UVP fault is tripped, the fault flag is set (fig-
ure 12). Using an external PMOSFET interfaced to the ¯ F ¯ ¯ A ¯ ¯ U ¯ ¯ L ¯ ¯ T ¯
pin (figure 13), the user can disconnect the IC from VIN during a
fault event.
Figure 9. Open LED condition during PWM dimming. (A) The LED string
(ch3, 100 mA/div.) is opened (no current flow through the LED pin) during
an off-period for the PWM dimming signal (ch4, 5 V/div.). (B) At the next
PWM cycle, the LED open condition is detected and the A8513 starts
boosting the output voltage (ch1, 10 V/div.). (C) Upon reaching the OVP
threshold and sensing no LED current flow, the A8513 shuts down and
sets the fault flag (ch2, 5 V/div.). (time = 10 ms/div.)
Figure 10. Open LED condition when PWM duty cycle is 100%. (A) The
LED string (ch3, 200 mA/div.) is opened (no current flow through the LED
pin). (B) The A8513 starts boosting the output voltage (ch1, 20 V/div.).
(C) Upon reaching the OVP threshold there is still no current flow through
the LED pin, and the A8513 shuts down and sets the fault flag (ch2,
5 V/div.). The LED pin voltage is ch4, 2 V/div. (time = 50 μs/div.)
C2
C1
C3
C4
C1
C2
C3
C4
A
A
The OVP pin is also used to detect
A
t
t
B
B
C
B
C
C
OUT
Wide Input Voltage Range, High Efficiency
short to
EN/PWM
FAULT
FAULT
I
V
V
V
I
LED
LED
LED
OUT
OUT
C4
C3
C1
C2
C3
C1
C2
C4
Figure 11. Power-up into an open LED situation. (A) A8513 enabled,
(B) fault flag (ch2, 5 V/div.) is set when OVP threshold is reached. Shows
V
5 V/div.), time = 1 ms/div..
Figure 12. Input disconnect switch function during an output short. (A) V
(ch1, 10 V/div.) falls during VOUT short to ground, (B) high peak current
present due to short, before the PMOSFET (ch3, 5 V/div.) is disconnected.
Shows input current (ch2, 10 A/div.) and fault flag (ch4, 5 V/div.),
time = 50 μs/div.
Figure 13. typical circuit for input disconnect switch.
OUT
V
PMOSFET Gate
FAULT
I
OUT
IN
(ch1, 20 V/div.), I
Fault Tolerant LED Driver
V
1
2N7002
IN
kΩ
A
LED
(ch3, 100 mA/div.), and EN/PWM (ch4,
A
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
1 kΩ
t
t
5 V
AO4421
10
B
kΩ
B
L1
A8513
FAULT
EN/PWM
FAULT
V
I
LED
OUT
12
OUT