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
■ Slope control with external cap
Applications
■ LED constant current supplying for varying
input voltages
■ Low voltage lighting
■ Small appliances LED lighting
■ Car LED lights
Description
The 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
components
STCS2A
2 A max constant current LED driver
10
1
PowerSO-10
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 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.
Table 1. Device summary
Order code Package Packaging
STCS2ASPR PowerSO-10 600 parts per reel
July 2008 Rev 3 1/18
www.st.com
18
Contents STCS2A
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1 Current setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2 Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.3 PWM dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.4 Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1 Reverse polarity protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.2 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/18
STCS2A Application diagram
1 Application diagram
Figure 1. Typical application diagram for 2 A LED current
V
V
IN
IN
4.5V up to 40V
4.5V up to 40V
BAT46ZFILM
BAT46ZFILM
R
100 ohm
R
100 ohm
IN
IN
C
C
0.1µF
0.1µF
ON
ON
OFF
OFF
ON
ON
OFF
OFF
Load disconnection
Load disconnection
(Open Drain output)
(Open Drain output)
BYP
BYP
V
V
CC
CC
PWM
PWM
EN
EN
DISC
DISC
C
C
SLOPE
SLOPE
10nF
10nF
STCS2A
STCS2A
SLOPE
SLOPE
GND
GND
FB
FB
DRAIN
DRAIN
SOURCE
SOURCE
R
R
FB
FB
0.05 ohm
0.05 ohm
C
C
DRAIN
DRAIN
0.47µF
0.47µF
3/18
Pin configuration STCS2A
2 Pin configuration
Figure 2. Pin connections (top view)
Table 2. Pin description
Pin n° Symbol Note
1V
2 PWM PWM dimming input
3ENShutdown
4 NC No connect
5 DRAIN Internal N-MOSFET drain
6 SOURCE
7FB
8 GND Ground
9 SLOPE Capacitor for slope control
10 DISC Load disconnection flag (open drain)
CC
exp-pad Internally connected to ground
Supply voltage
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
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
4/18
STCS2A Maximum ratings
3 Maximum ratings
Table 3. Absolute maximum ratings
Symbol Parameter Value Unit
V
CC
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 + V
+ 3.3 V
CC
SLOPE, FB Configuration pins -0.3 to + 3.3 V
ESD Human body model (all pins) ±2 kV
(1)
T
J
T
STG
1. TJ is calculated from the ambient temperature TA and the power dissipation PD according the following formula:
T
= TA + (PD x R
J
Junction temperature -40 to 150 °C
Storage temperature range -55 to 150 °C
). See Figure 16. for details of max power dissipation for ambient temperatures higher than 25 °C.
thJA
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 Parameter PowerSO-10 Unit
R
thJC
R
thJA
R
thJA
R
thJA
1. FR4 with using the recommended pad-layout
2. FR4 with heat sink on board (6 cm
3. FR4 with copper-filled through holes and external heat sink applied.
Thermal resistance junction-case 2 °C/W
Thermal resistance junction-ambient
Thermal resistance junction-ambient
Thermal resistance junction-ambient
2
).
(1)
(2)
(3)
50 °C/W
35 °C/W
12 °C/W
5/18
Electrical characteristics STCS2A
4 Electrical characteristics
Table 5. Electrical characteristics (V
C
DRAIN
= 1 µF; C
= 100 nF typical values are at TA = 25°C, unless otherwise specified)
BYP
= 12 V; IO = 100 mA; TJ = -40 °C to 125 °C; V
CC
DRAIN
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
CC
Supply voltage range 4.5 40 V
Output current range 1 2000 mA
I
O
Output current R
Regulation (percentage with
respect to V
V
FB
Feedback voltage IO = 0 to 2A 90 100 110 mV
CC
= 12 V)
= 50 mΩ 2A
FB
V
= 4.5 to 40 V,
CC
IO = 100 mA; V
DRAIN
= 1 V
-1 +1 %
On Mode 450 750
V
LEAK
TR/T
DISC
I
CC
DROP
DRAIN
T
D
Quiescent current (Measured on
VCC pin)
Dropout voltage (V
DRAIN
to GND)
Drain leakage current Shutdown; V
Rise/Fall time of the current on
F
PWM transition
Delay on PWM signal (Figure 1)
Low level voltage I
Leakage current V
Load disconnection threshold
DRAIN
-GND)
(V
Shutdown Mode;
= 5 to 12V
V
CC
Shutdown Mode;
V
= 12 to 40V
CC
I
= 100 mA 0.12 0.16
O
= 2 A 0.58 0.9
I
O
= 40 V 10 µA
DRAIN
C
T
V
C
V
C
= 10 nF,
SLOPE
= -40 °C to 105 °C
J
rising, V
PWM
= floating
SLOPE
falling, V
PWM
= floating
SLOPE
= 5 mA 0.2 0.5 V
SINK
= 5 V 1 µA
DISC
CC
CC
= 12 V
= 12 V
800 µs
3
1.2
DISC Turn-ON 75
DISC Turn-OFF 110
1
3
= 1 V;
µA
V
µs
mV
Thermal
Protection
Shutdown temperature 155
°C
Hysteresis 25
Logic inputs (PWM and EN)
V
V
Input low level 0.4 V
L
Input high level 1.2 V
H
EN, PWM leakage current V
PWM input leakage current V
= 5 V; V
EN
= 40 V 60
EN
= 40 V 120
PWM
= 5 V 2
PWM
µAEN input leakage current V
Note: All devices 100 % production tested at TA = 25 °C. Limits over the operating temperature
range are guaranteed by design.
6/18
STCS2A Timing
5 Timing
Figure 3. PWM and output current timing
PWM
PWM
90%
90%
10%
Current
Current
10%
Trise
Trise
T
T
D
D
Tfall
Tfall
T
T
D
D
Figure 4. Block diagram
High Voltage
High Voltage
45 V
45 V
Preregulator
V
V
CC
CC
EN
EN
PWM
PWMPWM
GND
GNDGND
Preregulator
3.3 V
3.3 V
Enable
Enable
Input
Input
PWM
PWM
Input
Input
Bandgap
Bandgap
Bandgap
1.23 V
1.23 V
1.23 V
Enable,
Enable,
PWM &
PWM &
Slope controll
Slope controll
Logic
Logic
SLOPE
SLOPE
Shutdown
Shutdown
all blocks
all blocks
Slope
Slope
Control
Control
100 mV
100 mV100 mV
75 mV
75 mV
FB
FB
Low Voltage 3.3 V
Low Voltage 3.3 V
Thermal
Thermal
Thermal
Shutdown
Shutdown
Shutdown
+
+-+
-
-
Comp
Comp
+
+-+
-
-
Logic
Logic
Disc
Disc
comp
comp
Driver
Driver
H.V.
H.V.
45 V
45 V
DISC
DISC
DRAIN
DRAIN
SOURCE
SOURCE
7/18
Typical performance characteristics STCS2A
6 Typical performance characteristics
Figure 5. I
Figure 7. I
vs VCC, TA = 25°C Figure 6. I
DRAIN
vs temperature Figure 8. V
DRAIN
vs R
DRAIN
1000
1000
100
100
[mA]
[mA]
DRAIN
DRAIN
I
I
10
10
1
1
0.1 1 10 100
0.1 1 10 100
DROP
SET
RFB[Ω]
RFB[Ω]
(including VFB) vs
temperature
Figure 9. ICC vs temperature Figure 10. ICC vs V
8/18
CC
STCS2A Typical performance characteristics
Figure 11. T
Figure 13. Dimming operation: Rise Figure 14. Dimming operation: Fall
rise/Tfall
vs C
SLOPE
Figure 12. Turn-on time
C
SLOPE
= 1 nF
C
SLOPE
= 1 nF
9/18
Detail description STCS2A
7 Detail description
The 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
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, R
the following equation:
R
= V
/ I
F
FB
= 100 mV / 700 mA = 142 mΩ
LEDs
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 (obtained with C
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 µs, this is important to implement synchronization among several light LED
sources.
should be selected according to
F
=0) which is around 4 µs each.
SLOPE
10/18
The rise and fall slope of the current is controlled by the C
time are linear dependent from the C
characteristics). A controlled rise time has two main benefits: reducing EMI noise and avoid
current spike at turn on.
When C
condition an overshoot can be present on the LED current before the system goes into
regulation.
is left floating, the internal switch is turned on at maximum speed, in this
SLOPE
capacitor value (see graph in typical
SLOPE
capacitor. The rise and fall
SLOPE
STCS2A Detail description
7.4 Diagnostic
When STCS2A is in on mode (EN is high), the device is able to detect disconnection or fail
of the LED string monitoring V
pulled low regardless the PWM pin status. This information can be used by the system to
inform that some problem happens in the LEDs.
DRAIN
pin. If V
is lower than 75 mV the DISC pin is
DRAIN
11/18
Application information STCS2A
8 Application information
8.1 Reverse polarity protection
STCS2A must be protected from reverse connection of the supply voltage. Since the current
sunk from V
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 V
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
pin is in the range of 450 µA a small diode connected to VCC is able to
CC
and GND, a negative
IN
V
V
IN
IN
BAT46
BAT46
or similar
or similar
V
V
CC
CC
PWM
PWM
DRAIN
DRAIN
DISC
DISC
+
+
C
C
SLOPE
SLOPE
8.2 Thermal considerations
The STCS2A 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 cm
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.
2
on-board heatsink.
EN
EN
ENEN
EN
ENEN
EN
SLOPE
SLOPE
GND
GND
FB
FB
SOURCE
SOURCE
R
R
SENSE
SENSE
12/18
The power dissipation in the device can be calculated as follow:
STCS2A Application information
PD = (V
basing on this and on the thermal resistance and ambient temperature, the junction
temperature can be calculated as:
T
= R
J
thJA
A typical application could be:
– Input voltage: 12 V;
– 3 white LEDs with an typical V
– LEDs current: 1000 mA;
– Package: PowerSO-10;
–T
In this case the drain voltage is given by:
V
DRAIN
end the power dissipated in the IC is the following:
P
= (1.2 - 0.1) x 1 + 12 x 0.5 x 10-3 = 1.1 W
D
With a thermal resistance junction-ambient equal to 12 °C/W the junction temperature is:
T
= 12 x 1.1 + 50 = 63 °C.
J
The following pictures show the maximum power dissipation according to the ambient
temperature:
- VFB) x I
DRAIN
x PD + T
= 50 °C;
A
= 12 - 3 x 3.6 = 1.2 V
A
LED
+ (V
CC
x ICC)
F
= 3.6 V;
Figure 16. Maximum power dissipation vs T
12.00
12.00
10.00
10.00
[W]
[W]
DMAX
DMAX
P
P
8.00
8.00
6.00
6.00
4.00
4.00
2.00
2.00
0.00
0.00
25 35 45 55 65 75 85 95 105 115 125
25 35 45 55 65 75 85 95 105 115 125
P
P
DMAX
DMAX
= (T
= (T
JMAX-TA
JMAX-TA
for PowerSO-10
A
)/R
)/R
thJA
thJA
[°C]
[°C]
R
R
thJA
thJA
[°C/W]
[°C/W]
12
12
35
35
13/18
Package mechanical data STCS2A
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.
14/18
STCS2A Package mechanical data
PowerSO-10 Mechanical Data
Dim.
A 3.70 0.146
A1 0.10 0.004
A2 3.40 3.60 0.134 0.142
A3 1.25 1.35 0.049 0.053
b 0.40 0.53 0.016 0.021
c0.35 0.55 0.014 0.022
D 9.40 9.60 0.370 0.378
D1 7.40 7.60 0.291 0.299
E13.80 14.40 0.543 0.567
E1 9.30 9.50 0.366 0.374
E2 7.20 7.60 0.283 0.299
E3 5.90 6.10 0.232 0.240
e 1.27 0.050
L0.95 1.65 0.037 0.065
α 0° 8°0° 8°
Min. Typ. Max. Min. Typ. Max.
mm. inch.
0068039-E
15/18
Package mechanical data STCS2A
Tape & Reel PowerSO-10 Mechanical Data
Dim.
Min. Typ. Max. Min. Typ. Max.
A 330 12.992
C 12.8 13.2 0.504 0.519
D 20.2 0.795
N60 2.362
T 30.4 1.197
Ao 14.9 15.1 0.587 0.594
Bo 9.9 10.1 0.3900.398
Ko 4.15 4.35 0.163 0.171
Po 3.9 4.1 0.153 0.161
P23.9 24.1 0.941 0.949
W23.7 24.3 0.933 0.957
mm. inch.
16/18
STCS2A Revision history
10 Revision history
Table 6. Document revision history
Date Revision Changes
19-Feb-2008 1 Initial release.
28-May-2008 2 Modified: Table 3 on page 5.
02-Jul-2008 3 Modified: Table 5 on page 6.
17/18
STCS2A
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