A8513 ALLEGRO [Allegro MicroSystems], A8513 Datasheet - Page 11

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

A8513
ISET pin. The limitation of this form of dimming is that the inter-
nal I
thus limiting the dimming ratios that can be achieved.
Figure 7, top panel is a typical application using a DAC to control
the LED current using a single resistor connected to the ISET pin.
The I
Where V
put voltage.
When the DAC voltage is equal to V
there is no current through R
to decrease, the ISET current starts to increase, thus increasing
the LED current. When the DAC voltage is 0 V, the LED current
will be at its maximum.
• For a dual-resistor configuration (lower panel of figure 7), the
ISET current is controlled by the following formula:
The advantage of this circuit is that the DAC voltage can be
higher or lower, thus adjusting the LED current to a higher or
Figure 7. Simplified diagram of voltage LED current control (upper) single
resistor, and (lower) dual resistors.
SET
SET
error amplifier is designed to work from 40 to 160 μA,
ISET
current is controlled by the following formula:
DAC
DAC
GND
GND
is the ISET pin voltage and V
VDAC
VDAC
I
I
SET
SET
=
=
V
V
R
ISET
ISET
ISET
ISET
R1
R
R
R
ISET
ISET
ISET
– V
–
. When the DAC voltage starts
DAC
V
ISET
DAC
, the internal reference,
R
– V
1
DAC
ISET
ISET
ISET
A8513
A8513
is the DAC out-
GND
GND
Wide Input Voltage Range, High Efficiency
(3)
(4)
lower value of the preset LED current set by the R
Output Overvoltage Protection (OVP) and Output
Undervoltage Protection (UVP)
The A8513 has output overvoltage protection (OVP), output
undervoltage protection and secondary overvoltage protection
(open diode).
Overvoltage Protection
of 1.218 V. A resistive divider can be used to set the V
voltage protection threshold up to 45 V (see figure 8). There is
no restriction on the value of the resistor chosen, but it is recom-
mended that the divider current be kept between 10 and 60 μA.
This will minimize the effect of sense current on the accuracy of
OVP, and minimize output voltage bleed-off during PWM dim-
ming.
Formulas for calculating the OVP resistor voltage divider are
shown below.
The OVP function is not inherently a latched fault. If the OVP
condition occurs during a load dump, the IC will stop switching
but not shut down.
Figure 8. Simplified diagram of the OVP pin functions.
▫ V
▫ V
▫ V
DAC
DAC
DAC
= 1.003 V; the output is strictly controlled by R
> 1.003 V; the LED current is reduced
< 1.003 V; the LED current is increased
Fault Tolerant LED Driver
R
R
OVP1
OVP2
= (V
= 1.218 V / I
The OVP pin has a threshold,
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
OVP
–
–
+
+
– 1.218 V) / I
1.218 V
100 mV
A8513
SET
OVP
VOUT
SET
ISET
R
R
OVP1
OVP2
OUT
resistor:
V
OVPHI(th)
ISET
over-
(5)
(6)
11
,