STCS1 1.5 A max constant current LED driver Features ■ Up to 40 V input voltage ■ Less than 0.5 V voltage overhead ■ Up to 1.5 A output current ■ PWM dimming pin ■ Shutdown pin ■ LED disconnection diagnostic DFN8 (3x3 mm) PowerSO-8 Applications ■ Supplying LEDs with constant current for varying input voltages ■ Low voltage lighting ■ Small appliance LED lighting ■ Car LED lights The current is set with external resistor up to 1.5 A with a ± 10 % precision; a dedicated pin allows implementing PWM dimming. An open-drain pin output provides information on load disconnection condition. Description The STCS1 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. Table 1. July 2008 Device summary Order codes Packages Packaging STCS1PUR DFN8 (3 x 3 mm) 3000 parts per reel STCS1PHR PowerSO-8 2500 parts per reel Rev 8 1/17 www.st.com 17 Contents STCS1 Contents 1 Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Detail description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8 7.1 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.3 PWM dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.4 Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1 Reverse polarity protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.2 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2/17 STCS1 Application diagram 1 Application diagram Figure 1. Typical application diagram for 0.5 A LED current VIN 4.5V to 40V BAT46ZFILM RIN 100 ohm CBYP 0.1µF ON PWM ON EN DISC OFF OFF DRAIN VCC Load disconnection (Open Drain output) STCS1 CDRAIN 0.47µF GND FB RFB 0.2 ohm 3/17 Pin configuration STCS1 2 Pin configuration Figure 2. Pin connections (top view) PowerSO-8 DFN8 Table 2. Pin description Pin n° Symbol 1 VCC 2 PWM 3 EN 4 DRAIN 5 FB 6 GND Ground 7 N.C. In order to guarantee the device works properly it is mandatory to leave this pin floating 8 DISC Load disconnection flag (open drain) Exp-pad 4/17 Note 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 Internally connected to ground STCS1 Maximum ratings 3 Maximum ratings Table 3. Absolute maximum ratings Symbol VCC Parameter Value Unit DC supply voltage -0.3 to +45 DRAIN Drain pin -0.3 to +45 PWM, EN, DISC Logic pins -0.3 to + VCC + 0.3 V -0.3 to + 3.3 V ±2 kV Junction temperature -40 to 150 °C Storage temperature range -55 to 150 °C FB ESD TJ (1) TSTG V Configuration pins Human body model (all pins) 1. TJ is calculated from the ambient temperature TA and the power dissipation PD according the following formula: TJ = TA + (PD x RthJA). See Figure 12 and Figure 13 for details of max power dissipation for ambient temperatures 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. Table 4. Thermal data Symbol RthJC RthJA Parameter Thermal resistance junction-case Thermal resistance junction-ambient DFN8 PowerSO-8 Unit 10 12 °C/W 37.6 (1) 45 (2) °C/W 1. This value is referred to four-layer PCB, JEDEC standard test board. 2. With two sides, two planes PCB following EIA/JEDEC JESD51-7 standard. 5/17 Electrical characteristics STCS1 4 Electrical characteristics Table 5. Electrical characteristics (VCC = 12 V; IO = 100 mA; TJ = -40 °C to 125 °C; VDRAIN = 1 V; CDRAIN = 1 µF; CBYP = 100 nF typical values are at TA = 25 °C, unless otherwise specified) Symbol VCC IO VFB Parameter Test conditions Min. VDROP 40 V Output current range 1 1500 mA Output current RFB = 0.2 Ω Regulation (percentage with respect to VCC=12V) VCC = 4.5 to 40 V, IO = 100 mA; VDRAIN = 1 V -1 Feedback voltage IO = 0 to 1.5A 90 Quiescent current (Measured on VCC pin) Dropout voltage (VDRAIN to GND) 500 mA +1 % 100 110 mV 450 750 Shutdown Mode; VCC = 5 to 12V 1 Shutdown Mode; VCC = 12 to 40V 3 IO = 100 mA 0.12 0.16 IO = 1.5 A 0.58 0.9 µA V Shutdown; VDRAIN = 40 V 10 VPWM rising, VCC = 12 V 3 VPWM falling, VCC = 12 V 1.2 Low level voltage ISINK = 5 mA 0.2 Leakage current VDISC = 5 V Load disconnection threshold (VDRAIN-GND) DISC Turn-ON 75 DISC Turn-OFF 110 Delay on PWM signal (see Figure 3) DISC Thermal Protection Unit 4.5 LEAKDRAIN Drain leakage current TD Max. Supply voltage range On Mode ICC Typ. µA µs 0.5 V 1 µA mV Shutdown temperature 155 Hysteresis 25 °C Logic inputs (PWM and EN) VL Input low level VH Input high level Note: 6/17 0.4 1.2 V V EN, PWM leakage current VEN = 5 V; VPWM = 5 V 2 EN input leakage current VEN = 40 V 60 PWM input leakage current VPWM = 40 V 120 µA All devices 100 % production tested at TA = 25 °C. Limits over the operating temperature range are guaranteed by design. STCS1 Timing 5 Timing Figure 3. PWM and output current timing PWM 90% Current 10% Trise TD Figure 4. Block diagram High Voltage 45 V VCC Tfall TD Preregulator 3.3 V Low Voltage 3.3 V H.V. 45 V Thermal Shutdown Bandgap 1.23 V DISC Shutdown all blocks + 75 mV EN PWM Enable Input PWM Input Enable & PWM Logic Disc comp DRAIN + 100 mV Logic - Driver Comp GND FB 7/17 Typical performance characteristics STCS1 6 Typical performance characteristics Figure 5. IDRAIN vs VCC, TA = 25 °C Figure 6. IDRAIN vs RSET Figure 7. IDRAIN vs temperature Figure 8. VDROP (including VFB) vs temperature Figure 9. ICC vs temperature Figure 10. ICC vs VCC 8/17 STCS1 7 Detail description Detail description The STCS1 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 1.5 A can be set according to the resistor value, the resulting output current has a tolerance of ± 10 %. For instance, should one need a 700 mA LEDs current, RF should be selected according to the following equation: RF = VFB / ILEDs = 100 mV / 700 mA = 142 mΩ 7.2 Enable When the enable pin is low the device completely off thus reducing current consumption to less than 1 µA. 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 which is around 4 µs 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 a short delay time TD (see Figure 3). 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 µs, this is important to implement synchronization among several light LED sources. 7.4 Diagnostic When STCS1 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. 9/17 Application information STCS1 8 Application information 8.1 Reverse polarity protection STCS1 must be protected from reverse connection of the supply voltage. Since the current sunk from VCC pin is in the range of 450 µA 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 11. Reverse polarity condition VIN BAT46 or similar VCC DRAIN PWM + 8.2 EN DISC GND FB Thermal considerations The STCS1 is able to control a LED current up to 1.5 A 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 Table 4: Thermal data section are the typical ones, in particular RthJA depends on the copper area and the number of layers of the printed circuit board under the pad. DFN8 and PowerSO-8 have an exposed die attach pad which enhances the thermal conductivity enabling high power application. 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: 500 mA; 10/17 STCS1 Application information – Package: DFN8 3x3 mm; – TA = 50 °C; In this case VDRAIN = 12 - 3 x 3.6 = 1.2 V PD = (1.2 - 0.1) x 0.5 + 12 x 0.5 x 10-3 = 0.55 + 6 x 10-3 = 556 mW The junction temperature will be: TJ = 37.6 x 0.556 + 50 = 70.9 °C. The following pictures show the maximum power dissipation according to the ambient temperature for both packages: Figure 12. Maximum power dissipation vs TA for DFN8 3x3 mm Figure 13. Maximum power dissipation vs TA for PowerSO-8 3.00 3.50 RthJA = 38 [°C/W] 3.00 PDMAX [W] PDMAX [W] 2.50 2.00 1.50 1.00 0.50 25 35 45 55 65 75 [°C] 2.00 1.50 1.00 0.50 PDMAX = (TJMAX-TA)/RthJA 0.00 RthJA = 45 [°C/W] 2.50 PDMAX = (TJMAX-TA)/RthJA 0.00 85 95 105 115 125 25 35 45 55 65 75 85 95 105 115 125 [°C] 11/17 Package mechanical data 9 STCS1 Package mechanical data In order to meet environmental requirements, ST offers these devices in ECOPACK® 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. 12/17 STCS1 Package mechanical data DFN8 (3x3 mm) mechanical data mm. mils. Dim. Min. Typ. Max. Min. Typ. Max. 0.80 0.90 1.00 31.5 35.4 39.4 A1 0.02 0.05 0.8 2.0 A2 0.70 27.6 A3 0.20 7.9 A b 0.18 D D2 2.23 7.1 2.38 1.49 1.64 2.48 87.8 0.40 11.8 93.7 97.7 118.1 1.74 58.7 0.50 0.30 9.1 118.1 3.00 e L 0.30 3.00 E E2 0.23 64.6 68.5 19.7 0.50 11.8 15.7 19.7 13/17 Package mechanical data STCS1 PowerSO-8 mechanical data Dim. mm. Min. Typ. A inch. Max. Min. Typ. 1.70 A1 0.00 A2 1.25 b 0.31 c 0.17 D 4.80 D1 0.067 0.00 0.006 0.049 0.142 0.51 0.012 0.020 0.25 0.007 0.010 4.90 5.00 0.189 0193 0.197 2.24 3.10 3.20 0.088 0.122 0.126 E 5.80 6.00 6.20 0.228 0.236 0.244 E1 3.80 3.90 4.00 0.150 0.154 0.157 E2 1.55 2.41 2.51 0.061 0.095 0.099 e 0.15 Max. 1.27 0.050 h 0.25 0.50 0.010 0.020 L 0.40 1.27 0.016 0.050 k 0° 8° 0° 8° ccc 0.10 0.004 7195016C 14/17 STCS1 Package mechanical data Tape & reel QFNxx/DFNxx (3x3) mechanical data mm. inch. Dim. Min. Typ. A Max. Min. Typ. 180 13.2 7.087 C 12.8 D 20.2 0.795 N 60 2.362 T Max. 0.504 0.519 14.4 0.567 Ao 3.3 0.130 Bo 3.3 0.130 Ko 1.1 0.043 Po 4 0.157 P 8 0.315 15/17 Revision history STCS1 10 Revision history Table 6. Document revision history Date Revision 10-Apr-2007 1 Initial release. 07-May-2007 2 PowerSO-8 mechanical data has been updated and the RthJC for PowerSO-8 value on Table 4 is changed. 24-May-2007 3 Change value CBYP 0.1µF ==> 1 µF on Figure 1 typical application. 27-Sep-2007 4 Add RIN on Figure 1 application diagram. 02-Oct-2007 5 Figure 1 updated. 15-Feb-2008 6 Modified: Figure 1 on page 3, Figure 4 on page 7, Figure 12 on page 11, Figure 13 on page 11. 05-May-2008 7 Modified: Table 2 on page 4, pin 7 description. 02-Jul-2008 8 Modified: Table 5 on page 6. 16/17 Changes STCS1 Please Read Carefully: Information in this document is provided solely in connection with ST products. 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