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STCS05A
0.5 A max constant current LED driver
Features

Up to 40 V input voltage Less than 0.5 V voltage overhead Up to 0.5 A output current PWM dimming pin Shutdown pin LED disconnection diagnostic Slope control with external cap
SO-8
Applications

LED constant current supplying for varying input voltages Low voltage lighting Small appliances LED lighting Car LED lights
components solution for driving LEDs in low voltage applications such as 5 V, 12 V or 24 V giving benefits in terms of precision, integration and reliability. The current is set with external resistor up to 0.5 A with a 10 % precision; a dedicated pin allows implementing PWM dimming. An external capacitor allows setting the slope for the current rise from tens of microseconds to tens of milliseconds allowing reduction of EMI. An open-drain pin output provides information on load disconnection condition.
Description
The STCS05A is a BiCMOS constant current source designed to provide a precise constant current starting from a varying input voltage source. The main target is to replace discrete
Table 1.
Device summary
Order code STCS05ADR Package SO-8 Packaging 2500 parts per reel
July 2008
Rev 2
1/18
www.st.com 18
Contents
STCS05A
Contents
1 2 3 4 5 6 7 Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Detail description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1 7.2 7.3 7.4 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 PWM dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1 8.2 Reverse polarity protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9 10
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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STCS05A
Application diagram
1
Figure 1.
Application diagram
Typical application diagram for 0.5 A LED current
VIN 4.5V to 40V
BAT46ZFILM
RIN 100 ohm
CBYP 0.1F
VCC PWM EN DISC SLOPE GND
DRAIN
ON OFF ON OFF
STCS05A
CDRAIN 0.47F
FB
RFB 0.2 ohm
Load disconnection (Open Drain output)
CSLOPE 10nF
3/18
Pin configuration
STCS05A
2
Figure 2.
Pin configuration
Pin connections (top view)
Table 2.
Pin n 1 2 3 4 5 6 7 8
Pin description
Symbol VCC PWM EN DRAIN FB GND SLOPE DISC Supply voltage PWM dimming input Shutdown pin Internal N-MOSFET drain Feedback input. The control loop regulates the current in such a way that the average voltage at the FB input is 100 mV (nominal). The cathode of the LED and a resistor to ground to set the LED current should be connected at this point. Ground Capacitor for slope control Load disconnection flag (open drain) Note
4/18
STCS05A
Maximum ratings
3
Table 3.
Maximum ratings
Absolute maximum ratings
Parameter DC supply voltage Drain pin Logic pins Configuration pins Human body model (all pins) SO-8 TA=25C (1) Junction temperature Storage temperature range Value -0.3 to +45 V -0.3 to +45 -0.3 to + VCC + 0.3 -0.3 to + 3.3 2 0.85 -40 to 150 -55 to 150 V V kV W C C Unit
Symbol VCC DRAIN PWM, EN, DISC SLOPE, FB ESD Power Dissipation TJ TSTG
1. See Figure 16 for details of max power dissipation for ambient temperature higher than 25 C
Note:
Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Thermal data
Parameter Thermal resistance junction-case Thermal resistance junction-ambient (1) SO-8 20 100 Unit C/W C/W
Table 4.
Symbol RthJC RthJA
1. This value depends from thermal design of PCB on which the device is mounted.
5/18
Electrical characteristics
STCS05A
4
Table 5.
Symbol VCC
Electrical characteristics
Electrical characteristics (VCC = 12 V; IO = 100 mA; TJ = -40 C to 125 C; VDRAIN = 1 V; CDRAIN = 1 F; CBYP = 100 nF typical values are at TA = 25 C, unless otherwise specified)
Parameter Supply voltage range Output current range IO Output current Regulation (percentage with respect to VCC = 12 V) VFB Feedback Voltage RFB = 0.2 VCC = 4.5 to 40V, IO = 100mA; VDRAIN = 1V IO = 0 to 0.5A On Mode ICC Quiescent current (Measured on VCC pin) Shutdown Mode; VCC = 5 to 12V Shutdown Mode; VCC = 12 to 40V VDROP Dropout voltage (VDRAIN to GND) IO = 100mA IO = 0.5A Shutdown; VDRAIN = 40V CSLOPE = 10 nF, TJ = -40 C to 105 C VPWM rising, VCC = 12V CSLOPE = floating, VPWM falling, VCC = 12V CSLOPE = floating ISINK = 5mA VDISC = 5V DISC Turn-ON DISC Turn-OFF 75 mV 110 155 C Hysteresis 25 800 3 s 1.2 0.2 0.5 1 V A 0.12 0.58 -1 90 100 450 Test conditions Min. 4.5 1 500 +1 110 750 1 3 0.16 V 0.9 10 A s A Typ. Max. 40 500 Unit V mA mA % mV
LEAKDRAIN Drain leakage current TR/TF Rise/Fall time of the current on PWM transition
TD
Delay on PWM signal (see Figure 3)
Low level voltage Leakage current DISC Load disconnection threshold (VDRAIN-GND) Thermal Protection Shutdown temperature
Logic inputs (PWM and EN) VL VH Input low level Input high level EN, PWM leakage current EN input leakage current PWM input leakage current VEN = 5V; VPWM = 5V VEN = 40V VPWM = 40V 1.2 2 60 120 A 0.4 V V
Note:
6/18
All devices 100 % production tested at TA = 25 C. Limits over the operating temperature range are guaranteed by design.
STCS05A
Timing
5
Figure 3.
Timing
PWM and output current timing
PWM
90%
Current
10%
TD
Trise
TD
Tfall
Figure 4.
Block diagram
High Voltage 45 V Preregulator 3.3 V Bandgap 1.23 V Shutdown all blocks
75 mV
Low Voltage 3.3 V Thermal Shutdown
H.V. 45 V
VCC
DISC + Disc comp
EN PWM
Enable Input PWM Input
Enable, PWM & Slope controll Logic
DRAIN
+
Logic
100 mV
Comp
Driver
GND
Slope Control
FB
SLOPE
7/18
Typical performance characteristics
STCS05A
6
Figure 5.
Typical performance characteristics
IDRAIN vs VCC, TA = 25 C Figure 6.
1000
IDRAIN vs RSET
100 IDRAIN [mA] 10 1 0.1
1 RFB []
10
100
Figure 7.
IDRAIN vs temperature
Figure 8.
VDROP (including VFB) vs temperature
Figure 9.
ICC vs temperature
Figure 10. ICC vs VCC
8/18
STCS05A
Typical performance characteristics
Figure 11. Trise/Tfall vs CSLOPE
Figure 12. Turn-on time
IDRAIN = 80 mA - CSLOPE = 10nF - TA = 25 C
VPWM 2V/DIV IDRAIN 20mA/DIV VDRAIN 1V/DIV Time 210sec/DIV
Figure 13. Rise time
IDRAIN = 80 mA - CSLOPE = 10nF - TA = 25 C
Figure 14. Fall time
IDRAIN = 80 mA - CSLOPE = 10nF - TA = 25 C
VPWM 2V/DIV IDRAIN 20mA/DIV VDRAIN 1V/DIV Time 200sec/DIV
VPWM 2V/DIV IDRAIN 20mA/DIV VDRAIN 1V/DIV Time 200sec/DIV
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Detail description
STCS05A
7
Detail description
The STCS05A is a BiCMOS constant current source designed to provide a precise constant current starting from a varying input voltage source. The main target is to replace discrete components solution for driving LEDs in low voltage applications such as 5 V, 12 V or 24 V giving benefits in terms of precision, integration and reliability.
7.1
Current setting
The current is set with an external sensing resistor connected to the FB pin. The feedback voltage is 100 mV, then a low resistor value can be chosen reducing power dissipation. A value between 1 mA and 500 mA can be set according to the resistor value, the resulting output current has a tolerance of 10 %. For instance, should one need a 350 mA LEDs current, RF should be selected according to the following equation: RF = VFB / ILEDs = 100 mV / 350 mA = 284 m
7.2
Enable
When the enable pin is low the device completely off thus reducing current consumption to less than 1 A. When in shutdown mode, the internal main switch is off.
7.3
PWM dimming
The PWM input allows implementing PWM dimming on the LED current; when the PWM input is high the main switch will be on and vice versa. A typical frequency range for the input is from few Hertz to 50 kHz. The maximum dimming frequency is limited by the minimum rise/fall time of the current (obtained with CSLOPE = 0) which is around 4 s each. Above 50 kHz the current waveforms starts assuming a triangular shape. While the PWM input is switching, the overall circuitry remains on, this is needed in order to implement two important features: short delay time and controlled slope for the current. Since the PWM pin is controlling just the main switch, the overall circuitry is always on and it is able to control the delay time between the PWM input signal and the output current in the range of few s, this is important to implement synchronization among several light LED sources. The rise and fall slope of the current is controlled by the CSLOPE capacitor. The rise and fall time are linear dependent from the CSLOPE capacitor value (see graph in typical characteristics). A controlled rise time has two main benefits: reducing EMI noise and avoid current spike at turn on. When CSLOPE is left floating, the internal switch is turned on at maximum speed, in this condition an overshoot can be present on the LED current before the system goes into regulation.
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STCS05A
Detail description
7.4
Diagnostic
When STCS05A is in on mode (EN is high), the device is able to detect disconnection or fail of the LED string monitoring VDRAIN pin. If VDRAIN is lower than 75 mV the DISC pin is pulled low regardless the PWM pin status. This information can be used by the system to inform that some problem happens in the LEDs.
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Application information
STCS05A
8
8.1
Application information
Reverse polarity protection
STCS05A must be protected from reverse connection of the supply voltage. Since the current sunk from VCC pin is in the range of 450 A a small diode connected to VCC is able to protect the chip. Care must be taken for the whole application circuit, especially for the LEDs, in fact, in case a negative voltage is applied between VIN and GND, a negative voltage will be applied to the LED string that must have a total breakdown voltage higher than the negative applied voltage in order to avoid any damage.
Figure 15. Reverse polarity condition
VIN
BAT46 or similar
VCC PWM
DRAIN
EN
+
DISC
SLOPE GND
FB
8.2
Thermal considerations
The STCS05A is able to control a LED current up to 500 mA and able to sustain a voltage on the drain pin up to 40 V. Those operating conditions are however limited by thermal constraints, the thermal resistances shown in the thermal data section is the typical ones. The power dissipation in the device can be calculated as follow: PD = (VDRAIN - VFB) x ILED + (VCC x ICC) basing on this and on the thermal resistance and ambient temperature, the junction temperature can be calculated as: TJ = RthJA x PD + TA A typical application could be: - Input voltage: 12 V; - 3 white LEDs with an typical VF = 3.6 V; - LEDs current: 350 mA; - Package: SO-8; - TA = 50 C;
12/18
STCS05A In this case VDRAIN = 12 - 3 x 3.6 = 1.2 V
Application information
PD = (1.2 - 0.1) x 0.35 + 12 x 0.5 x 10-3 = 0.385 + 6 x 10-3 = 391 mW The junction temperature will be: TJ = 100 x 0.391 + 50 = 89 C For a correct operation of the chip, the junction temperature must not exceed 110 C. The following pictures show the maximum power dissipation according to the ambient temperature:
Figure 16. Maximum power dissipation vs TA for SO-8
1.40 1.20
RthJA = 100 [C/W]
PDMAX [W]
1.00 0.80 0.60 0.40 0.20 25 35 45 55 65 75 [C] 85 95 105 115 125
PDMAX = (TJMAX-TA)/RthJA
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Package mechanical data
STCS05A
9
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK(R) packages. These packages have a lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
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STCS05A
Package mechanical data
SO-8 mechanical data
Dim. A A1 A2 B C D E e H h L k ddd 0.1 5.80 0.25 0.40 mm. Min. 1.35 0.10 1.10 0.33 0.19 4.80 3.80 1.27 6.20 0.50 1.27 8 (max.) 0.04 0.228 0.010 0.016 Typ. Max. 1.75 0.25 1.65 0.51 0.25 5.00 4.00 Min. 0.053 0.04 0.043 0.013 0.007 0.189 0.150 0.050 0.244 0.020 0.050 inch. Typ. Max. 0.069 0.010 0.065 0.020 0.010 0.197 0.157
0016023/C
15/18
Package mechanical data
STCS05A
Tape & reel SO-8 mechanical data
mm. Dim. Min. A C D N T Ao Bo Ko Po P 8.1 5.5 2.1 3.9 7.9 12.8 20.2 60 22.4 8.5 5.9 2.3 4.1 8.1 0.319 0.216 0.082 0.153 0.311 Typ. Max. 330 13.2 0.504 0.795 2.362 0.882 0.335 0.232 0.090 0.161 0.319 Min. Typ. Max. 12.992 0.519 inch.
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STCS05A
Revision history
10
Table 6.
Date
Revision history
Document revision history
Revision 1 2 Initial release. Modified: Table 5 on page 6. Changes
04-Mar-2008 02-Jul-2008
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STCS05A
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