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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 (3x3mm) Power SO-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.
Device summary
Order code STCS1PUR STCS1PHR Package DFN8 (3mm x 3mm) Power SO-8 Packaging 3000 parts per reel 2500 parts per reel
October 2007
Rev. 5
1/17
www.st.com 17
STCS1
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1 7.2 7.3 7.4 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 PWM Dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 8.2 Reverse polarity protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9 10
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
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STCS1
Application diagram
1
Figure 1.
Application diagram
Typical application diagram for 0.5 A LED current
VIN 4.5V to 40V
RIN(*) 100Ohm
CBYP 0.1F
VCC
ON
DRAIN
OFF ON OFF
PWM EN DISC
STCS1
GND FB
RFB 0.2Ohm
CDRAIN 0.47F
Load disconnection (Open Drain output)
(*) The RIN resistor must be inserted when dVCC/dt is higher than 10 V/s
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Pin configuration
STCS1
2
Figure 2.
Pin configuration
Pin connections (top view)
DFN8
PowerSO-8
Table 2.
Pln N 1 2 3 4 5 6 7 8
Pin description
Symbol VCC PWM EN DRAIN FB GND N.C. DISC Exp-pad Supply voltage PWM dimming input Shutdown pin Internal N-MOSFET drain External resistor connection for current set (N-MOSFET source) Ground Not connected Load disconnection flag (open drain) Internally connected to ground. Note
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STCS1
Maximum ratings
3
Table 3.
Maximum ratings
Absolute maximum ratings
Parameter DC supply voltage Drain voltage Logic pins Configuration pins Human body model (all pins) 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 -40 to 150 -55 to 150 V V kV C C Unit
Symbol VCC VD PWM, EN, DISC FB ESD TJ (1) TSTG
1. TJ is calculated from the ambient temperature TA and the power dissipation PD accoring 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 25C.
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 DFN8 10 37.6
(1)
Table 4.
Symbol RthJC RthJA
Power SO-8 12 45
(2)
Unit C/W 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.
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Electrical characteristics
STCS1
4
Table 5.
Electrical characteristics
Electrical characteristics (VCC = 12 V; IO = 100 mA; TA = -40C to 85C; VDRAIN = 1 V; CDRAIN = 1 F; CBYP = 100 nF typical values are at TA = 25C, unless otherwise specified)
Parameter Supply voltage range Output current range IO Output current Regulation (percentage with respect to VCC=12V) VFB ICC Feedback voltage Quiescent current (measured on VCC pin) RFB = 0.2 VCC = 4.5 to 40 V, IO = 100 mA; VDRAIN = 1 V All the current range On Mode Shutdown Mode; VCC = 5 to 40 V IO = 100 mA IO = 1.5 A Shutdown; VDRAIN = 40 V VPWM rising, VCC = 12 V VPWM falling, VCC = 12 V ISINK = 5 mA VDISC = 5 V DISC Turn-ON DISC Turn-OFF 75 mV 110 155 C Hysteresis 25 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 +1 110 650 A 1 0.16 V 0.9 10 A Typ. Max. 40 1500 Unit V mA mA % mV
Symbol VCC
VDROP
Dropout voltage (VDRAIN to GND)
LEAKDRAIN Drain leakage current 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 = 5 V; VPWM = 5 V VEN = 40 V VPWM = 40 V 1.2 2 50 100 A 0.4 V V
Note:
All devices 100% production tested at TA = 25C. Limits over the operating temperature range are guaranteed by design.
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STCS1
Timing
5
Figure 3.
Timing
PWM and output current timing
PWM
90%
Current
10%
TD
Trise
TD
Tfall
Figure 4.
Block diagram
7/17
Typical performance characteristics
STCS1
6
Figure 5.
Typical performance characteristics
IDRAIN vs VCC, TA = 25C 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
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STCS1
Detail description
7
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%.
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 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 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 s, 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.
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Application information
STCS1
8
8.1
Application information
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 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 11. Reverse polarity condition
VIN
BAT46 or similar
VCC PWM EN DISC
DRAIN
+
GND FB
8.2
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 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: 500mA;
10/17
STCS1 - Package: DFN8 3x3 mm; - TA = 50C; In this case VDRAIN = 12 - 3 x 3.6 = 1.2 V
Application information
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 = 70.9C. 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 3x3mm Figure 13. Maximum power dissipation vs TA for PowerSO-8
2.50 2.00
2.00 1.80 1.60 1.40
1.50
1.20 [W] 1.00 0.80 0.60
[W] 1.00
0.50 0.00 25 35 45 55 [C] 65 75 85
0.40 0.20 0.00 25 35 45 55 [C] 65 75 85
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Package mechanical data
STCS1
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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STCS1
Package mechanical data
DFN8 (3x3 mm) mechanical data
mm. Dim. Min. A A1 A2 A3 b D D2 E E2 e L 0.30 1.49 2.23 0.18 0.80 Typ. 0.90 0.02 0.70 0.20 0.23 3.00 2.38 3.00 1.64 0.50 0.40 0.50 11.8 1.74 58.7 2.48 87.8 0.30 7.1 Max. 1.00 0.05 Min. 31.5 Typ. 35.4 0.8 27.6 7.9 9.1 118.1 93.7 118.1 64.6 19.7 15.7 19.7 68.5 97.7 11.8 Max. 39.4 2.0 mils.
13/17
Package mechanical data
STCS1
PowerSO-8 mechanical data
Dim. A A1 A2 b c D D1 E E1 E2 e h L k ccc 0.25 0.40 0 0.00 1.25 0.31 0.17 4.80 2.24 5.80 3.80 1.55 4.90 3.10 6.00 3.90 2.41 1.27 0.50 1.27 8 0.10 0.010 0.016 0 0.51 0.25 5.00 3.20 6.20 4.00 2.51 mm. Min. Typ. Max. 1.70 0.15 0.00 0.049 0.012 0.007 0.189 0.088 0.228 0.150 0.061 0193 0.122 0.236 0.154 0.095 0.050 0.020 0.050 8 0.004 Min. inch. Typ. Max. 0.067 0.006 0.142 0.020 0.010 0.197 0.126 0.244 0.157 0.099
7195016C
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STCS1
Package mechanical data
Tape & reel QFNxx/DFNxx (3x3) mechanical data
mm. Dim. Min. A C D N T Ao Bo Ko Po P 3.3 3.3 1.1 4 8 12.8 20.2 60 14.4 0.130 0.130 0.043 0.157 0.315 Typ. Max. 180 13.2 0.504 0.795 2.362 0.567 Min. Typ. Max. 7.087 0.519 inch.
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Revision history
STCS1
10
Table 6.
Date
Revision history
Document revision history
Revision 1 2 3 4 5 Initial release. PowerSO-8 mechanical data has been updated and the RthJC for PowerSO-8 value on Table 4. is changed. Change value CBYP 0.1F ==> 1 F on Figure 1. typical application. Add RIN on Figure 1. application diagram. Figure 1. updated. Changes
10-Apr-2007 07-May-2007 24-May-2007 27-Sep-2007 02-Oct-2007
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STCS1
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