2 A max constant current LED driver - st.com

1 July 2008 Rev 31/1818 STCS2A2 A max constant current LED driverFeatures Up to 40 V input voltage Less than V voltage overhead Up to 2 A output current PWM dimming pin Shutdown pin LED disconnection diagnostic Slope control with external capApplications LED constant current supplying for varying input voltages Low voltage lighting Small appliances LED lighting Car LED lightsDescriptionThe STCS2A 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 componentssolution for driving LEDs in low voltage applications such as 5 V, 12 V or 24 V giving benefits in terms of precision, integration and current is set with external resistor up to 2 A with a 10 % precision; a dedicated pin allows implementing PWM dimming.

2 An external capacitor allows setting the slope for the current rise from tens of microseconds to tens of milliseconds allowing reduction of open-drain pin output provides information on load disconnection summaryOrder codePackagePackagingSTCS2 ASPRP owerSO-10600 parts per diagram .. 32 Pin configuration .. 43 Maximum ratings .. 54 Electrical characteristics .. 65 Timing .. 76 Typical performance characteristics .. 87 Detail description .. setting .. dimming .. 118 Application information .. polarity protection .. considerations .. 129 Package mechanical data .. 1410 Revision history .. 17 STCS2 AApplication diagram3/181 Application diagram Figure application diagram for 2 A LED current up to ohmLoad disconnection(Open Drain output)OFFOFFONONPWMENGNDSLOPEVCCDISCFBD RAINSOURCERIN 100 up to ohmLoad disconnection(Open Drain output)OFFOFFONONPWMENGNDSLOPEVCCDISCFBD RAINSOURCERIN 100 ohmBAT46 ZFILMPin configurationSTCS2A4/182 Pin configuration Figure connections (top view) Table 2.

3 Pin descriptionPin n SymbolNote1 VCCS upply voltage2 PWMPWM dimming input3 ENShutdown4 NCNo connect5 DRAINI nternal N-MOSFET drain6 SOURCEI nternal N-MOSFET source. Reference voltage is 100 mV. An external resistor between SOURCE and GND pins sets different current levels for different application needs7 FBFeedback 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 point8 GNDG round9 SLOPEC apacitor for slope control10 DISCLoad disconnection flag (open drain)exp-padInternally connected to groundSTCS2 AMaximum ratings5/183 Maximum ratings Note:Absolute maximum ratings are those values beyond which damage to the device may occur.

4 Functional operation under these conditions is not maximum ratingsSymbolParameterValueUnitVCCDC supply to +45 VDRAIND rain to +45 SOURCES ource to + , EN, DISCL ogic to + VCC + , FBConfiguration to + body model (all pins) 2kVTJ (1)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 16. for details of max power dissipation for ambient temperatures higher than 25 temperature-40 to 150 CTSTGS torage temperature range-55 to 150 CTable dataSymbolParameterPowerSO-10 UnitRthJCThermal resistance junction-case2 C/WRthJAThermal resistance junction-ambient (1)50 C/WRthJAThermal resistance junction-ambient (2)35 C/WRthJAThermal resistance junction-ambient (3)12 C/W1.

5 FR4 with using the recommended pad-layout2. FR4 with heat sink on board (6 cm2).3. FR4 with copper-filled through holes and external heat sink characteristicsSTCS2A6/184 Electrical characteristicsNote:All devices 100 % production tested at TA = 25 C. Limits over the operating temperature range are guaranteed by 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)SymbolParameterTest voltage current range12000mAIOO utput current RFB = 50 m 2 ARegulation (percentage with respect to VCC = 12 V)VCC = to 40 V, IO = 100 mA; VDRAIN = 1 V-1+1%VFBF eedback voltageIO = 0 to 2A90100110mVICCQ uiescent current (Measured on VCC pin)On Mode450750 AShutdown Mode;VCC = 5 to 12V1 Shutdown Mode;VCC = 12 to 40V3 VDROPD ropout voltage (VDRAIN to GND)IO = 100 = 2 leakage currentShutdown.

6 VDRAIN = 40 V10 ATR/TFRise/Fall time of the current on PWM transitionCSLOPE = 10 nF,TJ = -40 C to 105 C800 sTDDelay on PWM signal (Figure 1)VPWM rising, VCC = 12 V CSLOPE = floating3 sVPWM falling, VCC = 12 V CSLOPE = level voltageISINK = 5 currentVDISC = 5 V1 ALoad disconnection threshold (VDRAIN-GND) DISC Turn-ON75mVDISC Turn-OFF110 ThermalProtectionShutdown temperature155 CHysteresis25 Logic inputs (PWM and EN)VLInput low high , PWM leakage currentVEN = 5 V; VPWM = 5 V2 AEN input leakage currentVEN = 40 V60 PWM input leakage currentVPWM = 40 V120 STCS2 ATiming7/185 TimingFigure and output current timing PWM10%90%TDTriseTDTfallCurrentPWM10%90%T DTriseTDTfallCurrentFigure diagram High Voltage 45 V+-+-DriverDisc compDISCDRAINSOURCE75 mVEnable,PWM &Slope controllLogicShutdown all blocksThermal ShutdownLow Voltage 45 V100 mVCompLogicVCCENPWMGNDS lope ControlFBSLOPEHigh Voltage 45 V+-+-+-+-DriverDisc compDISCDRAINSOURCE75 mVEnable.

7 PWM &Slope controllLogicShutdown all blocksThermal ShutdownThermal ShutdownLow Voltage 45 V100 mV100 mVCompLogicVCCENPWMPWMGNDGNDS lope ControlFBSLOPET ypical performance characteristicsSTCS2A8/186 Typical performance characteristicsFigure vs VCC, TA = 25 CFigure vs RSET Figure vs temperatureFigure (including VFB) vs temperature Figure vs temperatureFigure 10. ICC vs VCC [mA]RFB[ ] [mA]RFB[ ]STCS2 ATypical performance characteristics9/18 Figure 11. Trise/Tfall vs CSLOPEF igure 12. Turn-on time Figure 13. Dimming operation: RiseFigure 14. Dimming operation: Fall CSLOPE = 1 nF CSLOPE = 1 nFDetail descriptionSTCS2A10/187 Detail descriptionThe STCS2A is a BiCMOS constant current source designed to provide a precise constant current starting from a varying input voltage source.

8 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 current settingThe 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 2 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 m EnableWhen the enable pin is low the device completely off thus reducing current consumption to less than 1 A.

9 When in shutdown mode, the internal main switch is 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 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 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 rise and fall slope of the current is controlled by the CSLOPE capacitor.

10 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 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 description11 DiagnosticWhen STCS2A 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 informationSTCS2A12/188 Application Reverse polarity protectionSTCS2A must be protected from reverse connection of the supply voltage.