July 2008 Rev 4 1/16
16
STCS2
2 A max constant current LED driver
Features
■Up to 40 V input voltage
■Less than 0.5 V voltage overhead
■Up to 2 A output current
■PWM dimming pin
■Shutdown pin
■LED disconnection diagnostic
Applications
■LED constant current supplying for varying
input voltages
■Low voltage lighting
■Small appliances LED lighting
■Car LED lights
Description
The STCS2 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.
The current is set with external resistor up to 2 A
with a ± 10 % precision; a dedicated pin allows
implementing PWM dimming.
An open-drain pin output provides information on
load disconnection condition.
PowerSO-10
1
10
Table 1. Device summary
Order code Package Packaging
STCS2SPR PowerSO-10 600 parts per reel
www.st.com
Contents STCS2
2/16
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
7.1 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.3 PWM dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.4 Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 Reverse polarity protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
STCS2 Application diagram
3/16
1 Application diagram
Figure 1. Typical application diagram for 2 A LED current
VIN
4.5V up to 40V
CDRAIN
0.47µF
STCS2
CBYP
0.1µF
RFB
0.05 ohm
Load disconnection
(Open Drain output)
OFF
OFF
ON
ON
PWM
EN
GND
VCC
DISC FB
DRAIN
SOURCE
RIN 100 ohm
VIN
4.5V up to 40V
CDRAIN
0.47µF
STCS2
CBYP
0.1µF
RFB
0.05 ohm
Load disconnection
(Open Drain output)
OFF
OFF
ON
ON
PWM
EN
GND
VCC
DISC FB
DRAIN
SOURCE
RIN 100 ohm
Pin configuration STCS2
4/16
2 Pin configuration
Figure 2. Pin connections (top view)
Table 2. Pin description
Pin n° Symbol Note
1V
CC Supply voltage
2 PWM PWM dimming input
3ENShutdown
4 N.C. Not connected
5 DRAIN Internal N-MOSFET drain
6 SOURCE
Internal N-MOSFET SOURCE. Reference voltage is 100 mV. An external resistor
between SOURCE and GND pins sets different current levels for different application
needs
7FB
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
8 GND Ground
9 N.C. In order to guarantee the device works properly it is mandatory to leave this pin floating
10 DISC Load disconnection flag (open drain)
Exp-pad Internally connected to ground
STCS2 Maximum ratings
5/16
3 Maximum ratings
Note: Absolute maximum ratings are those values beyond which damage to the device may occur.
Functional operation under these conditions is not implied.
Table 3. Absolute maximum ratings
Symbol Parameter Value Unit
VCC DC supply voltage -0.3 to +45 V
DRAIN Drain pin -0.3 to +45
SOURCE Source pin -0.3 to + 3.3 V
PWM, EN, DISC Logic pins -0.3 to + VCC + 0.3 V
FB Configuration pins -0.3 to + 3.3 V
ESD Human body model (all pins) ±2 kV
TJ (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 12 for details of max power dissipation for ambient temperatures higher than 25°C.
Junction temperature -40 to 150 °C
TSTG Storage temperature range -55 to 150 °C
Table 4. Thermal data
Symbol Parameter PowerSO-10 Unit
RthJC Thermal resistance junction-case 2 °C/W
RthJA Thermal resistance junction-ambient (1) 50 °C/W
RthJA Thermal resistance junction-ambient (2) 35 °C/W
RthJA Thermal resistance junction-ambient (3) 12 °C/W
1. FR4 with using the recommended pad-layout
2. FR4 with heat sink on board (6 cm2).
3. FR4 with copper-filled through holes and external heat sink applied.
Electrical characteristics STCS2
6/16
4 Electrical characteristics
Note: All devices 100 % production tested at TA = 25 °C. Limits over the operating temperature
range are guaranteed by design.
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 Parameter Test conditions Min. Typ. Max. Unit
VCC Supply voltage range 4.5 40 V
Output current range 1 2000 mA
IOOutput current RFB = 50 mΩ2A
Regulation (percentage with
respect to VCC=12V)
VCC = 4.5 to 40 V,
IO = 100 mA; VDRAIN = 1 V -1 +1 %
VFB Feedback voltage IO = 0 to 2A 90 100 110 mV
ICC
Quiescent current (Measured on
VCC pin)
On Mode 450 750
µA
Shutdown Mode;
VCC = 5 to 12V 1
Shutdown Mode;
VCC = 12 to 40V 3
VDROP Dropout voltage (VDRAIN to GND) IO = 100 mA 0.12 0.16 V
IO = 2 A 0.58 0.9
LEAKDRAIN Drain leakage current Shutdown; VDRAIN = 40 V 10 µA
TDDelay on PWM signal (see fig.1) VPWM rising, VCC = 12 V 3 µs
VPWM falling, VCC = 12 V 1.2
DISC
Low level voltage ISINK = 5 mA 0.2 0.5 V
Leakage current VDISC = 5 V 1 µA
Load disconnection threshold
(VDRAIN-GND)
DISC Turn-ON 75 mV
DISC Turn-OFF 110
Thermal
Protection
Shutdown temperature 155 °C
Hysteresis 25
Logic inputs (PWM and EN)
VLInput low level 0.4 V
VHInput high level 1.2 V
EN, PWM leakage current VEN = 5 V; VPWM = 5 V 2
µAEN input leakage current VEN = 40 V 60
PWM input leakage current VPWM = 40 V 120
STCS2 Timing
7/16
5 Timing
Figure 3. PWM and output current timing
PWM
10%
90%
TDTrise TDTfall
Current
PWM
10%
90%
TDTrise TDTfall
Current
Figure 4. Block diagram
High Voltage
45 V
Preregulator
3.3 V
Enable
Input
PWM
Input
Bandgap
1.23 V
+
-
+
-
Driver
Disc
comp
DISC
DRAIN
75 mV
Enable
&
PWM
Logic
Shutdown
all blocks
Thermal
Shutdown
Low Voltage 3.3 V H.V.
45 V
100 mV
Comp
Logic
VCC
EN
PWM
GND SOURCE
FB
High Voltage
45 V
Preregulator
3.3 V
Enable
Input
PWM
Input
Bandgap
1.23 V
Bandgap
1.23 V
+
-
+
-
+
-
+
-
Driver
Disc
comp
DISC
DRAIN
75 mV
Enable
&
PWM
Logic
Shutdown
all blocks
Thermal
Shutdown
Thermal
Shutdown
Low Voltage 3.3 V H.V.
45 V
100 mV100 mV
Comp
Logic
VCC
EN
PWM
GNDGND SOURCE
FB
Typical performance characteristics STCS2
8/16
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
1
10
100
1000
0.1 1 10 100
I
DRAIN
[mA]
R
FB
[Ω]
1
10
100
1000
0.1 1 10 100
I
DRAIN
[mA]
R
FB
[Ω]
STCS2 Detail description
9/16
7 Detail description
The STCS2 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 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 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 STCS2 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.
Application information STCS2
10/16
8 Application information
8.1 Reverse polarity protection
STCS2 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.
8.2 Thermal considerations
The STCS2 is able to control a LED current up to 2 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 poor thermal conduction of epoxy FR4 boards does not permit to benefit of the
outstanding thermal performance of the PowerSO-10.
In any case one way to improve the thermal conduction is the use of large heat spreader
areas at the copper layer of the PC board. This leads to a reduction of thermal resistance to
30 - 36°C/W for 3 to 6 cm2 on-board heatsink.
Use of copper-filled through holes on conventional FR4 techniques increases the
metallization and decreases thermal resistance accordingly. Using a configuration with 16
holes under the spreader of the package with a pitch of 1.8 mm and a diameter of 0.7 mm,
the thermal resistance (junction - heatsink) can be reduced to 12 °C/W.
The thermal resistances shown in the Error! Reference source not found. section are the
typical ones.
The power dissipation in the device can be calculated as follow:
PD = (VDRAIN - VFB) x ILED + (VCC x ICC)
Figure 11. Reverse polarity condition
PWM
EN
GND
V
CC
DRAIN
DISC
FB
V
IN
+
or similar
BAT46
RSENSE
SOURCE
PWM
EN
GND
V
CC
DRAIN
DISC
FB
V
IN
+
or similar
BAT46
RSENSE
SOURCE
STCS2 Application information
11/16
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: 1000 mA;
– Package: Power SO-10;
–T
A = 50 °C;
In this case the drain voltage is given by:
VDRAIN = 12 - 3 x 3.6 = 1.2 V
end the power dissipated in the IC is the following:
PD = (1.2 - 0.1) x 1 + 12 x 0.5 x 10-3 = 1.1 W
With a thermal resistance junction-ambient equal to 12 °C/W the junction temperature is:
TJ = 12 x 1.1 + 50 = 63 °C.
The following pictures show the maximum power dissipation according to the ambient
temperature:
Figure 12. Maximum power dissipation vs TA for PowerSO-10
0.00
2.00
4.00
6.00
8.00
10.00
12.00
25 35 45 55 65 75 85 95 105 115 125
[°C]
12
35
R
thJA
[°C/W]
P
DMAX
[W]
P
DMAX
= (T
JMAX
-T
A
)/R
thJA
0.00
2.00
4.00
6.00
8.00
10.00
12.00
25 35 45 55 65 75 85 95 105 115 125
[°C]
12
35
R
thJA
[°C/W]
P
DMAX
[W]
P
DMAX
= (T
JMAX
-T
A
)/R
thJA
Package mechanical data STCS2
12/16
9 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.
STCS2 Package mechanical data
13/16
Dim. mm. inch.
Min. Typ. Max. Min. Typ. Max.
A3.70 0.146
A1 0.10 0.004
A2 3.40 3.60 0.134 0.142
A31.25 1.35 0.0490.053
b0.40 0.530.016 0.021
c0.35 0.55 0.014 0.022
D9.40 9.60 0.370 0.378
D1 7.40 7.60 0.291 0.299
E13.80 14.40 0.5430.567
E1 9.309.50 0.366 0.374
E2 7.20 7.60 0.283 0.299
E35.90 6.10 0.232 0.240
e 1.27 0.050
L0.95 1.65 0.037 0.065
α0° 8°0° 8°
PowerSO-10 mechanical data
0068039-E
Package mechanical data STCS2
14/16
Dim.
mm. inch.
Min. Typ. Max. Min. Typ. Max.
A330 12.992
C 12.813.2 0.504 0.519
D 20.2 0.795
N60 2.362
T30.4 1.197
Ao 14.915.1 0.587 0.594
Bo 9.910.1 0.390 0.398
Ko 4.15 4.35 0.1630.171
Po 3.94.1 0.1530.161
P23.924.1 0.941 0.949
W23.7 24.30.933 0.957
Tape & reel PowerSO-10 mechanical data
STCS2 Revision history
15/16
10 Revision history
Table 6. Document revision history
Date Revision Changes
03-Oct-2007 1 Initial release.
15-Feb-2008 2 Modified: Figure 1 on page 3, Figure 4 on page 7, Figure 12 on page 11.
05-May-2008 3 Modified: Table 2 on page 4, pin 9 description.
02-Jul-2008 4 Modified: Table 5 on page 6.
STCS2
16/16
Please Read Carefully:
Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the
right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any
time, without notice.
All ST products are sold pursuant to ST’s terms and conditions of sale.
Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no
liability whatsoever relating to the choice, selection or use of the ST products and services described herein.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this
document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products
or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such
third party products or services or any intellectual property contained therein.
UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED
WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS
OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZED ST REPRESENTATIVE, ST PRODUCTS ARE NOT
RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING
APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY,
DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE
GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK.
Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void
any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any
liability of ST.
ST and the ST logo are trademarks or registered trademarks of ST in various countries.
Information in this document supersedes and replaces all information previously supplied.
The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners.
© 2008 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -
Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
