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
Applications
STCS1
1.5 A max constant current LED driver
DFN8 (3x3 mm)
PowerSO-8
■ Supplying LEDs with constant current for
varying input voltages
■ Low voltage lighting
■ Small appliance LED lighting
■ Car LED lights
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.
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.
Table 1. Device summary
Order codes Packages Packaging
STCS1PUR DFN8 (3 x 3 mm) 3000 parts per reel
STCS1PHR PowerSO-8 2500 parts per reel
July 2008 Rev 8 1/17
www.st.com
17
Page 2
Contents STCS1
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2/17
Page 3
STCS1 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
STCS1
STCS1
GND
GND
DRAIN
DRAIN
FB
FB
R
R
FB
FB
0.2 ohm
0.2 ohm
C
C
DRAIN
DRAIN
0.47µF
0.47µF
3/17
Page 4
Pin configuration STCS1
2 Pin configuration
Figure 2. Pin connections (top view)
DFN8
PowerSO-8
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 N.C. In order to guarantee the device works properly it is mandatory to leave this pin floating
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
4/17
Page 5
STCS1 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
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:
= TA + (PD x R
T
J
than 25°C.
Junction temperature -40 to 150 °C
Storage temperature range -55 to 150 °C
). See Figure 12 and Figure 13 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 PowerSO-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
5/17
Page 6
Electrical characteristics STCS1
4 Electrical characteristics
Table 5. Electrical characteristics
(V
= 12 V; IO = 100 mA; TJ = -40 °C to 125 °C; V
CC
nF typical values are at T
= 25 °C, unless otherwise specified)
A
Symbol Parameter Test conditions Min. Typ. Max. Unit
DRAIN
= 1 V; C
DRAIN
= 1 µF; C
BYP
= 100
V
CC
I
O
V
FB
I
CC
V
DROP
LEAK
DRAIN
T
D
DISC
Thermal
Protection
Supply voltage range 4.5 40 V
Output current range 1 1500 mA
Output current R
Regulation (percentage with
respect to V
CC
=12V)
= 0.2 Ω 500 mA
FB
V
= 4.5 to 40 V,
CC
IO = 100 mA; V
DRAIN
= 1 V
-1 +1 %
Feedback voltage IO = 0 to 1.5A 90 100 110 mV
On Mode 450 750
Quiescent current (Measured on
VCC pin)
Shutdown Mode;
= 5 to 12V
V
CC
Shutdown Mode;
V
= 12 to 40V
CC
I
= 100 mA 0.12 0.16
Dropout voltage (V
DRAIN
to GND)
O
= 1.5 A 0.58 0.9
I
O
Drain leakage current Shutdown; V
rising, V
V
Delay on PWM signal
(see Figure 3)
Low level voltage I
Leakage current V
Load disconnection threshold
DRAIN
-GND)
(V
PWM
falling, V
V
PWM
= 5 mA 0.2 0.5 V
SINK
= 5 V 1 µA
DISC
DISC Turn-ON 75
DISC Turn-OFF 110
= 40 V 10 µA
DRAIN
= 12 V 3
CC
= 12 V 1.2
CC
1
µA
3
V
µs
mV
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.
6/17
Page 7
STCS1 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
PWM
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
Logic
Logic
Shutdown
Shutdown
all blocks
all blocks
100 mV
100 mV100 mV
75 mV
75 mV
+
+-+
-
-
Comp
Comp
Low Voltage 3.3 V
Low Voltage 3.3 V
Thermal
Thermal
Thermal
Shutdown
Shutdown
Shutdown
+
+-+
-
-
Disc
Disc
comp
comp
Logic
Logic
Driver
Driver
H.V.
H.V.
45 V
45 V
DISC
DISC
DRAIN
DRAIN
FB
FB
7/17
Page 8
Typical performance characteristics STCS1
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
8/17
CC
Page 9
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 %.
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 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.
should be selected according to
F
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 V
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 pulled
DRAIN
9/17
Page 10
Application information STCS1
8 Application information
8.1 Reverse polarity protection
STCS1 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 11. 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
DRAIN
DRAIN
+
+
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 Table 4: Thermal data section are the typical ones, in
particular R
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 circuit
thJA
- VFB) x I
LED
+ (V
CC
x ICC)
PWM
PWM
EN
EN
DISC
DISC
GND
GND
FB
FB
10/17
T
= R
J
x PD + T
thJA
A
A typical application could be:
– Input Voltage: 12 V;
– 3 white LEDs with an typical V
– LEDs current: 500 mA;
= 3.6 V;
F
Page 11
STCS1 Application information
– 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 12. 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 13. 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]
11/17
Page 12
Package mechanical data STCS1
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.
12/17
Page 13
STCS1 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
13/17
Page 14
Package mechanical data STCS1
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.
14/17
7195016C
Page 15
STCS1 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
15/17
Page 16
Revision history STCS1
10 Revision history
Table 6. Document revision history
Date Revision Changes
10-Apr-2007 1 Initial release.
07-May-2007 2
PowerSO-8 mechanical data has been updated and the R
value on Ta bl e 4 is changed.
for PowerSO-8
thJC
24-May-2007 3 Change value C
27-Sep-2007 4 Add R
02-Oct-2007 5 Figure 1 updated.
15-Feb-2008 6
05-May-2008 7 Modified: Table 2 on page 4, pin 7 description.
02-Jul-2008 8 Modified: Table 5 on page 6.
Modified: Figure 1 on page 3, Figure 4 on page 7, Figure 12 on page 11,
Figure 13 on page 11.
on Figure 1 application diagram.
IN
0.1µF ==> 1 µF on Figure 1 typical application.
BYP
16/17
Page 17
STCS1
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