Transcript
STEVAL-ILL067V1 Six-channel ALED7707-based LED driver with embedded boost converter for automotive interior lighting and TFT backlighting Data brief
Description The purpose of this evaluation board is to provide an application example of a six-channel, mediumcurrent LED driver using the ALED7707 chip. The monolithic boost converter provides the required LED supply voltage starting from a single supply rail, while the brightness of the LED strings connected to the six outputs is controlled through a PWM signal. Open LED and LED short-circuit fault conditions are detected and managed. The board has been designed to provide a compact reference solution for automotive applications involving several LEDs arranged in multiple strings (e.g. interior lighting, infotainment LCD backlighting, etc.).
Features
Wide DC input voltage (6 V - 32 V) Six 70 mA output channels (capable of 30 mA to 85 mA each) PWM brightness control (10 µs minimum dimming on-time) Up to 10 white LEDs per channel (36 V OVP threshold) > 90% efficiency (VIN=12 V, VBOOST=30 V, fSW =1 MHz, no snubber) On-board input filter for conducted EMI reduction RoHS compliant All automotive-grade components
June 2015
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For further information contact your local STMicroelectronics sales office
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Board description and efficiency measurement
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Board description and efficiency measurement Figure 1: Basic connection of the STEVAL-ILL067V1 evaluation board
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GSPG10062015DI1514
For a quick evaluation of the STEVAL-ILL067V1 performance, just connect a DC power supply (e.g. 12 V & 3 A current capability) between the VIN (J1) and GND (J2) terminals and a set of suitable LED strings between the VBOOST (J3) & ROW1-ROW6 (J10 through J15) terminals. The SW1 & SW2 jumpers should be both set in the lower postion, while the SW4 jumper should be in the right position (FSW & MODE pins forced high, DIM pin high, see Table 3 for details) as per default setting. As soon as the supply input is powered, the EN pin (floating) is internally pulled-up, a soft-start sequence takes place and the LED strings are powered at full-brightness. By pressing SW3 (EN pin tied low), the device shutsdown. This pushbutton allows to easily reset the device in case a latched turn-off occurs as 2/10
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STEVAL-ILL067V1 Board description and efficiency measurement a consequence of a faulty condition (LED short-circuit, open string). To evaluate the PWM dimming capability, simply connect a pulse generator between the DIM terminal and ground (see figure 1) and remove the SW4 jumper to avoid any conflict between the external PWM signal and the +5 V rail. The frequency of the PWM signal should be in the 100 Hz - 20 kHz range, with a 10us minimum pulse duration and a 3.0 V to 5 V amplitude. Figure 2: STEVAL-ILL067V1 evaluation board PCB, top view
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Figure 3: STEVAL-ILL067V1 evaluation board PCB, bottom view
Table 1: STEVAL-ILL067V1 connectors
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Connector
Name
Function
J1
VIN+
Power supply input, positive terminal
J2
GND
Ground. This terminal has to be preferred as return for the power supply input.
J3
VBOOST
Boost converter output. Connect this terminal to the common anode of the LED strings to be driven.
J4
GND
Quiet ground terminal. To be used as reference ground for all control signals.
J5
SYNC
Switching frequency synchronization output. A synchronization clock is available at this pin.
J6
FAULT
Faulty condition indicator. Open drain output, tied low by the device when a faulty condition is detected. Also used to drive the D2 LED.
J7
DIM
PWM dimming control input. The output current generators are activated according to this pin to perform a PWM brightness control of the LEDs.
J8
EN
Device Enable input. Internally pulled-up. If tied low the device turns-off.
J9
FSW
J10
ROW1
Switching frequency synchronization input. An external clock (30% max duty-cycle) can be provided at this terminal to synchronize the boost converter.
J11
ROW2
J12
ROW3
J13
ROW4
Output terminals (channels). A low-side current generator is connected to each output. Connect to the kathode of the LED strings. Unused channels can be left floating.
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Board description and efficiency measurement
Connector
Name
J14
ROW5
J15
ROW6
Function
Table 2: STEVAL-ILL067V1 test points Test point
Function
AVCC
+5 V LDO output monitor (device supply rail).
COMP
COMP pin monitor (output of the trans-conductance amplifier of the control loop).
Table 3: STEVAL-ILL067V1 jumpers and switches Jumper / switch
Function
SW1
FSW pin assignment. When the jumper is set in the upper position (FSW to R5), the switching frequency of the boost converter is set by R5 (1 MHz). In the lower position (FSW to VCC), the FSW pin is tied high and the 630 kHz fixed switching frequency is set. In case an external synchronization clock has to be applied at the FSW pin, this jumper must be in the upper position.
SW2
MODE pin setting. This jumper allows to set high (VCC) or low (GND) the MODE pin in order to select the desired LED fault management. I case some channels are not used, the MODE pin must be set high.
SW3
EN low pushbutton. When pressed the EN pin (internally pulled-up) is tied to ground. Used to restart the device in case a latched turn-off due to a faulty condition.
SW4
DIM pin setting. If the jumper is set in the right position (VCC), the DIM pin is held high and the LEDs are driven at full-brightness as soon as the EN pin goes high. If the jumper is set in the left position (D3), the EN pin is pulled-down by R12 and activated by the PWM signal applied at the DIM pin through D3. This way a single-wire control is achieved (automatic device turn-on as soon as PWM dimming is applied). Note:D3 (BAT54K) & R12 (220k) are natively not mounted.
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Figure 4: STEVAL-ILL067V1 efficiency (fsw=1 MHz) GSPG10062015DI1530
92 Vin=8V 91
Vin=10V Vin=12V
90
Vin=14V Vin=16V
Efficiency
89 88 87 86 85 84
83 82 10
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18
20
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24
26
Output voltage (V)
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Board description and efficiency measurement
Figure 5: STEVAL-ILL067V1 efficiency with and w/o the R13-C14 snubber (fsw=1 MHz) GSPG10062015DI1535
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92
Efficiency
90
88
86 Vin=8V Vin=12V Vin=16V
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Vin=8V no snubber Vin=12V no snubber Vin=16V no snubber
82 10
12
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Output voltage (V)
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GND
EN
DIM
FAULT
J2
J8
J7
J6
100k
R 10
EN _LOW
SW 3
D2 F AU LT LED
DI M D3
4n7
C 16
N. M.
R9 100k
SW 4
1k
R 11
AV C C
AV C C
N. M.
R 12
MO D E
SW 2
C O MP
4n7
C7
2k 4
R3
1
21
5
20
22
7
ALED7707
C9
R6 26 k 1
R7 180k
TH PD
R OW 1 R OW 2 R OW 3 R OW 4 R OW 5 R OW 6
PG N D
SLOPE
OVSEL
25
11 12 13 14 15 16
17
9
18
R2 18k
R1 560k
L8
L7
0R 6
0R 6
0R 6
0R 6
L5
L6
0R 6
0R 6
L4
L3
C 15 220p
R8 680k
C 20
220p
C 19
220p
C 18
220p
10u
10u
C 17
C 11
C 10
FSW 390k
3n3
220p
C 22
220p
C 21
R5
C O MP
EN
MO D E
DI M
F AU LT
LD O5
AV C C
U1
R 13 8R 2
470p
C 14
STPS1L40-Y
100p
F SW
SW 1
R4 4R 7
6
XAL7030-103
D1
220p
J9
AV C C
470n
470n
24
C8
C5
C6
AV C C
AV C C
C4 10u
SY N C F SW
C3 10u
23 4
C2 47u
SS
J5
XAL5030-102
VIN RI LI M
SYNC
C1 100n
8 2
L2
19
L1
BI LI M
J1
LX SG N D
8/10 3
10u
C 12
100n
C 13
J 15
J 14
J 13
J 12
J 11
J 10
J4
J3
ROW6
ROW5
ROW4
ROW3
ROW2
ROW1
GND
VBOOST
2
10
VIN
Schematic diagram STEVAL-ILL067V1
Schematic diagram Figure 6: STEVAL-ILL067V1 circuit schematic
STEVAL-ILL067V1
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Revision history
Revision history Table 4: Document revision history Date
Version 12-Jun-2015
Changes 1
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Initial release.
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STEVAL-ILL067V1
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