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PDF A6217 Data sheet ( Hoja de datos )

Número de pieza A6217
Descripción PWM Dimmable Buck Regulator LED Driver
Fabricantes Allegro 
Logotipo Allegro Logotipo



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A6217 and A6217-1
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
FEATURES AND BENEFITS
• AEC-Q100 qualified
• 6 to 48 V supply voltage
• True average output current control
• 3 A maximum output over operating temperature range
(1.5 A for A6217-1)
• Cycle-by-cycle current limit
• Integrated MOSFET switch
• Enable / PWM dimming via direct logic input or power
supply voltage
• Internal control loop compensation
• Undervoltage lockout (UVLO) and thermal shutdown
protection
• Low power shutdown (1 µA typical)
• Robust protection against:
▫ Adjacent pin-to-pin short
▫ Pin-to-GND short
▫ Component open/short faults
• Enhancements over A6213:
▫ Dithering of switching frequency to reduce EMI
▫ Able to drive single white LED from 18 V supply at 2.2 MHz
▫ Smaller package option
PACKAGES:
10-pin DFN with
wettable flank
(suffix EJ)
Not to scale
8-pin SOICN
(suffix LJ)
DESCRIPTION
The A6217 is a single IC switching regulator that provides
constant-current output to drive high-power LEDs. It integrates
a high-side N-channel DMOS switch for DC-to-DC step- down
(buck) conversion. A true average current is output using a
cycle-by-cycle, controlled on-time method.
Output current is user-selectable by an external current sense
resistor. Output voltage is automatically adjusted to drive
various numbers of LEDs in a single string. This ensures the
optimal system efficiency.
LED dimming is accomplished by a direct logic input pulse-
width-modulation (PWM) signal at the enable pin.
The device is provided in a 3 mm × 3 mm wettable flank 10-pin
DFN (suffix EJ) or an 8-pin narrow SOIC (suffix LJ), both with
exposed pad for enhanced thermal dissipation. Both packages
are lead (Pb) free, with 100% matte-tin leadframe plating.
APPLICATIONS:
Automotive lighting
• Daytime running lights
• Front and rear fog lights
• Turn/stop lights
• Map light
• Dimmable interior lights
VIN (6 to 48 V)
TYPICAL APPLICATION CIRCUIT
GND C1
EN
1, 2
R1 3
VIN
TON
A6217
(EJ)
SW
BOOT
9,10
8 C4
4 EN
5 CS
PAD GND 7
VCC 6
Enable/PWM Dimming
(100 Hz to 2 kHz)
C5
L1
D1
LED+
LED
RSENSE
A6217-DS

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A6217 pdf
A6217 and
A6217-1
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
CHARACTERISTIC PERFORMANCE
C1,C2
C3
C4
Panel 1A. VIN = 7 V
Panel 1B. VIN = 12 V
Panel 1C. VIN = 18 V
Figure 1: Startup waveforms from off-state at various input voltages. Note that there is a fixed startup delay of ~70 µs before switching
starts. Subsequent rise time of the LED current depends on input/output voltages, inductor value, and switching frequency.
• Operating conditions: LED voltage = 3.5 V, LED current = 1.5 A, R1 = 73.2 kΩ (frequency = 1 MHz in steady state), L1 = 15 µH,
VIN = 7 V (panel 1A), 12 V (panel 1B), and 18 V (panel 1C)
• Oscilloscope settings: CH1 (Red) = VIN (5 V/div), CH2 (Blue) = VSW (5 V/div),
CH3 (Green) = iLED (500 mA/div), CH4 (Yellow) = Enable (5 V/div), time scale = 20 µs/div
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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A6217 arduino
A6217 and
A6217-1
Automotive-Grade, Constant-Current
PWM Dimmable Buck Regulator LED Driver
As another example, the waveform in Figure 11 shows the fault
case where external Schottky diode D1 is missing or open. As
LED current builds up, a larger-than-normal negative voltage is
developed at the SW node during off-time. This voltage trips the
missing Schottky detection function of the IC. The IC then shuts
down immediately, and waits for a cool-down period before retry.
Component Selections
The inductor is often the most critical component in a buck con-
verter. Follow the procedure below to derive the correct param-
eters for the inductor:
1. Determine the saturation current of the inductor. This can be
done by simply adding 20% to the average LED current:
iSAT ≥ iLED × 1.2.
2. Determine the ripple current amplitude (peak-to-peak value).As
a general rule, ripple current should be kept between 10% and
30% of the average LED current:
0.1 < iRIPPLE(pk-pk) / iLED < 0.3.
3. Calculate the inductance based on the following equations:
where
L = (VIN – VOUT ) × D × t / iRIPPLE , and
D = (VOUT + VD1 ) / ( VIN + VD1 ) ,
D is the duty cycle,
t is the period 1/ fSW , and
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
0.5 1 1.5
LED Current (A)
L = 10 µH
L = 15 µH
L = 22 µH
L = 33 µH
L = 47 µH
2
Figure 12: Inductance selection based on iLED and fSW ;
VIN = 12 V, VOUT = 6 V, ripple current = 20%
VD1 is the forward voltage drop of the Schottky diode
D1 (see figure 7).
Inductor Selection Chart
The chart in Figure 12 summarizes the relationship between
LED current, switching frequency, and inductor value. Based on
VIN
L1 LED+
SW
D1
iRIPPLE
VIN
SW
D1
L1 LED+
C1
iRIPPLE
CS
VRIPPLE
LED–
RSENSE
CS
VRIPPLE
LED–
RSENSE
Without output capacitor:
Ripple current through LED string is proportional to ripple voltage
at CS pin.
With a small capacitor across LED string:
Ripple current through LED string is reduced, while ripple voltage
at CS pin remains high.
Figure 13. Ripple current and voltage, with and without shunt capacitor
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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