Page 1
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
■ 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
STCS1A
1.5 A max constant current LED driver
DFN8 (3 x 3 mm)
The current is set with external resistor up to 1.5
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.
Power SO-8
The STCS1A 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 codes Packages Packaging
STCS1APUR DFN8 (3 x 3 mm) 3000 parts per reel
STCS1APHR Power SO-8 2500 parts per reel
July 2008 Rev 2 1/19
www.st.com
19
Page 2
Contents STCS1A
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2/19
Page 3
STCS1A Application diagram
1 Application diagram
Figure 1. Typical application diagram for 0.5 A LED current
V
V
IN
IN
4.5V to 40V
4.5V to 40V
BAT46ZFILM
BAT46ZFILM
RIN100 ohm
RIN100 ohm
OFF
OFF
OFF
OFF
C
C
BYP
BYP
0.1µF
0.1µF
ON
ON
ON
ON
Load disconnection
Load disconnection
(Open Drain output)
(Open Drain output)
V
V
PWM
PWM
EN
EN
CC
CC
DISC
DISC
STCS1A
STCS1A
C
C
SLOPE
SLOPE
10nF
10nF
DRAIN
DRAIN
C
C
DRAIN
DRAIN
0.47µF
0.47µF
FB
FB
GNDSLOPE
GNDSLOPE
R
R
FB
FB
0.2 ohm
0.2 ohm
3/19
Page 4
Pin configuration STCS1A
2 Pin configuration
Figure 2. Pin connections (top view)
DFN8
Table 2. Pin description
Pin n° Symbol Note
1V
2 PWM PWM dimming input
3 EN Shutdown pin
4 DRAIN Internal N-MOSFET drain
5FB
6 GND Ground
7 SLOPE Capacitor for slope control
8 DISC Load disconnection flag (open drain)
CC
Exp-pad Internally connected to ground.
Supply voltage
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.
PowerSO-8
4/19
Page 5
STCS1A 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
PWM, EN, DISC Logic pins -0.3 to + V
+ 0.3 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 accoring the following formula:
= TA + (PD x R
T
J
than 25°C.
Junction temperature -40 to 150 °C
Storage temperature range -55 to 150 °C
). See Figure 16 and Figure 17 for details of max power dissipation for ambient temperatures higher
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 DFN8 Power SO-8 Unit
R
thJC
R
thJA
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.
Thermal resistance junction-case 10 12 °C/W
Thermal resistance junction-ambient 37.6
(1)
45
(2)
°C/W
5/19
Page 6
Electrical characteristics STCS1A
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 1500 mA
I
O
Output current R
Regulation (percentage with
respect to V
V
FB
Feedback voltage IO = 0 to 1.5A 90 100 110 mV
CC
=12V)
= 0.2 Ω 500 mA
FB
V
= 4.5 to 40 V,
CC
IO = 100mA; 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
(see 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
= 1.5 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.
6/19
Page 7
STCS1A 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
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
FB
FB
7/19
Page 8
Typical performance characteristics STCS1A
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
DROP
SET
(including VFB) vs
temperature
Figure 9. ICC vs Temperature Figure 10. ICC vs V
8/19
CC
Page 9
STCS1A 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
= floating
SLOPE
C
SLOPE
= 1nF
C
SLOPE
= 1nF
9/19
Page 10
Detail description STCS1A
7 Detail description
The STCS1A 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 for instance, should one need a 700 mA LEDs current, R
selected according to the following equation:
should be
F
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 4µs each.
SLOPE
10/19
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
Page 11
STCS1A Detail description
7.4 Diagnostic
When STCS1A 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
11/19
Page 12
Application information STCS1A
8 Application information
8.1 Reverse polarity protection
STCS1A 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
V
V
IN
IN
IN
IN
BAT46
BAT46
or similar
or similar
or similar
or similar
V
V
V
V
CC
CC
CC
CC
DRAIN
DRAIN
DRAIN
DRAIN
+
+
+
+
8.2 Thermal considerations
The STCS1A 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 R
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:
P
= (V
D
DRAIN
basing on this and on the thermal resistance and ambient temperature, the junction
temperature can be calculated as:
depends on the copper area and the number of layers of the printed
thJA
- VFB) x I
LED
+ (V
CC
x ICC)
PWM
PWM
PWM
PWM
EN
EN
EN
EN
DISC
DISC
DISC
DISC
FB
FB
FB
FB
GNDSLOPE
GNDSLOPE
GNDSLOPE
GNDSLOPE
12/19
T
= R
J
x PD + T
thJA
A
A typical application could be:
– Input voltage: 12 V;
– 3 white LEDs with an typical V
=3.6 V;
F
Page 13
STCS1A Application information
– LEDs current: 500 mA;
– Package: DFN8 3x3 mm;
–T
= 50°C;
A
In this case V
P
= (1.2 - 0.1) x 0.5 + 12 x 0.5 x 10-3 = 0.55 + 6 x 10-3 = 556 mW
D
= 12 - 3 x 3.6 = 1.2 V
DRAIN
The junction temperature will be:
T
= 37.6 x 0.556 + 50 = 70.9 °C
J
The following pictures show the maximum power dissipation according to the ambient
temperature for both packages:
Figure 16. Maximum power dissipation vs T
3.50
3.50
3.00
3.00
2.50
2.50
2.00
2.00
[W]
[W]
1.50
1.50
DMAX
DMAX
P
P
1.00
1.00
0.50
0.50
0.00
0.00
for DFN8 3x3 mm
R
= 38 [°C/W]
R
= 38 [°C/W]
thJA
thJA
P
= (T
P
= (T
DMAX
DMAX
25 35 45 55 65 75 85 95 105 115 125
25 35 45 55 65 75 85 95 105 115 125
JMAX-TA
JMAX-TA
)/R
)/R
thJA
thJA
[°C]
[°C]
A
Figure 17. Maximum power dissipation vs TA
for PowerSO-8
3.00
3.00
2.50
2.50
2.00
2.00
[W]
[W]
1.50
1.50
DMAX
DMAX
1.00
1.00
P
P
0.50
0.50
P
= (T
P
= (T
DMAX
0.00
0.00
DMAX
25 35 45 55 65 75 85 95 105 115 125
25 35 45 55 65 75 85 95 105 115 125
JMAX-TA
JMAX-TA
)/R
)/R
thJA
thJA
[°C]
[°C]
R
R
thJA
thJA
= 45 [°C/W]
= 45 [°C/W]
13/19
Page 14
Package mechanical data STCS1A
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.
14/19
Page 15
STCS1A Package mechanical data
DFN8 (3x3 mm) mechanical data
mm. mils.
Dim.
Min. Typ. Max. Min. Typ. Max.
A0.800.90 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
b 0.18 0.23 0.307.1 9.1 11.8
D 3.00 118.1
D2 2.23 2.38 2.4887.893.7 97.7
E 3.00 118.1
E2 1.49 1.64 1.74 58.7 64.6 68.5
e 0.50 19.7
L0.30 0.40 0.50 11.8 15.7 19.7
15/19
Page 16
Package mechanical data STCS1A
PowerSO-8 mechanical data
Dim.
A 1.70 0.067
A1 0.00 0.15 0.00 0.006
A2 1.25 0.049 0.142
b 0.31 0.51 0.012 0.020
c 0.17 0.25 0.007 0.010
D4.804.90 5.00 0.189 0193 0.197
D1 2.24 3.10 3.20 0.088 0.122 0.126
E5.80 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 1.27 0.050
h 0.25 0.50 0.010 0.020
L 0.40 1.27 0.016 0.050
k0° 8°0° 8°
ccc 0.10 0.004
Min. Typ. Max. Min. Typ. Max.
mm. inch.
16/19
7195016C
Page 17
STCS1A Package mechanical data
Tape & reel QFNxx/DFNxx (3x3) mechanical data
mm. inch.
Dim.
Min. Typ. Max. Min. Typ. Max.
A180 7.087
C 12.8 13.2 0.504 0.519
D 20.2 0.795
N60 2.362
T 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
17/19
Page 18
Revision history STCS1A
10 Revision history
Table 6. Document revision history
Date Revision Changes
19-Feb-2008 1 Initial release.
02-Jul-2008 2 Modified: Table 5 on page 6.
18/19
Page 19
STCS1A
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