UL
®
LSI/CSI
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
V
DD
(+V )
BCV
TEST
SYNC
1
2
3
4
LS7642
LS7642FO
(631) 271-0400 FAX (631) 271-0405
October 2009
A3800
VOLTAGE CONTROLLED LIGHT DIMMER with SOFT ON/OFF
FEATURES:
• Analog input for direct control of illumination
• Soft turn-on or turn-off with touch or pushbutton
• Controls high-voltage Halogen or Incandescent lamps
• Controls low-voltage halogen lamps via
magnetic or electronic transformers
• Automatic safety shutdown for magnetic transformers
• Controls CFLs and fluorescent lamps via dimming ballasts
• Extension input for remote operation
• Suited for 50Hz or 60Hz AC
• Single 5V power supply
•
LS7642, LS7642FO
(DIP);
LS7642-S, LS7642FO-S
(SOIC)
- See Figure 1 -
GENERAL DESCRIPTION
LS7642
is an innovative light dimmer allowing direct control of il-
lumination with analog voltage. The analog voltage applied at the
brightness control input directly controls the conduction angle of
a triac in series with the lamp. For manual dimming applications
such as, wall switches, floor and table lamps etc, a sliding or ro-
tary potentiometer with a center tap can serve as the controlling
element. For automated applications such as uC controlled il-
lumination, dawn, dusk and daylight emulation in chicken coops
etc., the control voltage can be provided by the uC with built-in or
external D/A converter creating accurate control of dimming pat-
terns. Turn-on and turn-off of the lamp is made with a touch or
push-button or uC signal applied at the SENSE/ input or the EXT
input. In both turn-on and turn-off events, the brightness is softly
ramped up and ramped down, respectively.
SAFETY SHUTDOWN:
A typical electronic dimmer may not operate properly with the in-
ductive load encountered when driving a magnetic transformer-
coupled low-voltage halogen lamp. The inductive load may cause
a phenomenon called half-waving wherein the triac fires in al-
ternate AC half cycles leading to thermal destruction of the load
transformer. This problem is addressed by the
LS7642
in two
steps as described below:
1. Delayed triac turn-off.
When a trigger pulse is due to occur at a conduction angle which
coincides with the on state of the triac, the trigger pulse is de-
layed until the triac has turned off. This eliminates the underlying
cause of half-waving.
2. Delayed triac turn-on.
With inductive loads, the holding current needed to maintain the
triac on state may seriously lag behind the gate trigger signal
causing the triac to turn off prematurely. If the frequency of oc-
currences of the delayed turn-on exceeds a preset threshold, a
shutdown is initiated by turning off the trigger pulses. The safety
shutdown threshold value is accumulated in a 4-bit up/down
counter. The count increments for every occurrence of delayed
turn-on and decrements once every 8 AC cycles. If the count
reaches 15, the safety shutdown is invoked.
7642-102009-1
PIN ASSIGNMENT - TOP VIEW
LSI
FIGURE 1
8
7
6
5
TRIG/
V
SS
(-V )
EXT
SENS/
INPUT/OUTPUT DESCRIPTION:
V
DD
(Pin 1) Supply voltage positive terminal.
BCV
(Pin 2) Brightness control input. The voltage applied at the BCV
input controls the triac conduction angle and hence the brightness of
the lamp. The brightness varies in direct proportion to the applied volt-
age. For manual control of brightness, the BCV voltage can be sup-
plied from the center tap of a potentiometer connected between V
DD
and V
SS
. In non-manual instrumentation application where a uC is the
controlling agent, the BCV voltage can directly be provided by the uC.
The dynamic range of the BCV voltage is between 25% and 88% of
the applied power supply. For V
DD
= 5.0V this translates to a range be-
tween 1.25V for the minimum brightness and 4.4V for the maximum
brightness. There are 81 discrete brightness steps of 1.4
o
/39mV in-
crements in the dynamic range of 1.25V and 4.4V of the BCV voltage.
The corresponding conduction angles are 45
o
at the dimmest and
159
o
at the brightest.
TEST
(Pin 3) For factory use only, should be left unconnected.
SYNC
(Pin 4) The AC line frequency is applied to this input for syn-
chronizing all internal timings relative to the AC zero crossing. The
load on/off status information is also derived from this input for en-
forcing the safety shutdown protocol.
SENS/
(Pin 5) A momentary logic low applied to this input either with
a touch or a push-button switch, causes the state of the TRIG/ output
to switch; the lamp is turned on if the pre-touch state was off and
turned off if the pre-touch state was on. When turning on the bright-
ness is softly ramped up from off through minimum to the brightness
set by the BCV input. When turning off the brightness is softly ramped
down from the pre-touch brightness to off. The ramp rate for either
case is 1.4
o
/33.3ms at 60Hz or 1.4
o
/40ms at 50Hz.
EXT
(Pin 6) The EXT input has the same functionality as the SENS/
input. It is designed to discriminate ac pick-ups when remotely locat-
ed touch plates are connected to the dimmer units with long cables. A
logic high is the active level at the EXT input.
V
SS
(Pin 7) Supply voltage negative terminal.
LS7642
LS7642FO
TRIG/
(Pin 8) The TRIG/ can be turned on or off by applying the active
logic level at either the SENS/ or the EXT input for a brief duration. In
the Off state, the TRIG/ sits at steady high level turning off the triac in
series with the lamp. In the On state, the TRIG/ outputs a low going
pulse once every half cycle of the AC at a conduction angle set by the
voltage at the BCV input.
Upon power up the TRIG/ output defaults to the following
states:
For
LS7642
the TRIG/ is off.
For
LS7642FO
the TRIG/ is on
ABSOLUTE MAXIMUM RATINGS:
PARAMETER
DC supply voltage
Any input voltage
Operating temperature
Storage temperature
SYMBOL
V
DD
- Vss
V
IN
T
A
T
STG
VALUE
+7
Vss - 0.3 to V
DD
+ 0.3
0 to +90
-65 to +150
UNIT
V
V
o
C
o
C
DC ELECTRICAL CHARACTERISTICS:
(T
A
= +25
o
C, all voltages referenced to V
SS
. V
DD
= +5V unless otherwise noted.)
PARAMETER
Supply voltage
Supply current
SYNC
Lo
SYNC
Hi
BCV input:
Dynamic Voltage Range
Voltage increment per step
EXT, SENS/
Lo
EXT, SENS/
Hi
TRIG/
Lo
TRIG/
Hi
TRIG/
Sink Current
SYMBOL
V
DD
I
DD
V
ISL
V
ISH
Vb
∆Vb/∆ø
V
IEL
V
IEH
V
OL
V
OH
I
TSNK
MIN
4.5
-
-
2.9
1.25
-
-
3.5
-
-
35
TYP
5.0
300
-
-
-
39
-
-
0.2
5.0
-
MAX
5.5
400
2.1
-
4.4
-
1.5
-
-
-
-
UNIT
V
µA
V
V
V
mV
V
V
V
V
mA
CONDITION
-
Output unloaded, V
DD
= 5V
-
-
V
DD
= 5V
∆ø
= 1.4
o
, V
DD
= 5V
-
-
-
-
V
OTRIG
= 2.5V
TRANSIENT CHARACTERISTICS
(See Figures 2, 3 and 4):
PARAMETER
SYNC
Frequency
EXT, SENS/
Touch Duration
TRIG/
pulse width (see Note 2)
Conduction Angle
ø incremental steps
(Note 1)
On/Off slew rate
SYMBOL
f
S
T
S1
T
S1
T
W
T
W
ø
∆ø
S
S
S
S
MIN
40
67
80
-
-
45
-
-
-
TYP
-
-
-
130
156
-
1.4
1.4
1.4
MAX
70
infinite
infinite
-
-
159
-
-
-
UNI T
Hz
ms
ms
µs
µs
deg
deg
deg/33.33ms
deg/40ms
CONDITION
-
60Hz
50Hz
60Hz
50Hz
-
-
60Hz
50Hz
Note 1:
Total number of steps = 82.
Note 2:
T
W
= 488us (60Hz), 586us (50Hz) available. Contact factory for details.
7642-042908-2
FIGURE 4. TRIG/ OUTPUT CONDUCTION ANGLE, Ø
SYNC
ø
The information included herein is believed to be
accurate and reliable. However, LSI Computer Systems,
Inc. assumes no responsibilities for inaccuracies, nor for
any infringements of patent rights of others which may
result from its use.
TRIG/
T
W
P
**C6
MT1
**R9
MT2
G
FIGURE 5. A Typical Halogen Lamp Dimmer Wall Switch
SEE NOTE 2
R8
C5
R3
R7
EXTN
P
T
+
Z
D1
C2
ELECTRONIC
EXTENSION
(FIG. 7)
-
C4
R5
SEE NOTE 3
TOUCH
PLATE
R6
115VAC
OR
220VAC
L
C1
8
R10
TRIG/
7
V
SS
6
EXT
5
SENS/
R1
C7
V
DD
LS7642
BCV TEST SYNC
1
2
3
R2
4
R4
C3
SEE
NOTE 4
N
LAMP
R11
R12
1.
All circuits connected by broken lines are optional.
2. C5
is used only with electronic extension
and
R7
is used only with pushbutton switch.
3.
Connection between Pin 6 & Pin 7 should
be broken when EXT is used.
4.
Magnetic transformer should have thermal protection.
5.
Some electronic transformers may require larger values
of
C2,
sensitive gate triacs and snubber networks.
C2
values may have to be adjusted to be as high as 0.47uF
for 115VAC and 0.33uF for 220VAC. Sensitive gate triacs
are chosen for their low holding current. Typical triacs are
L4004L6 and L4004F51 for 115VAC and L6004L6 and
L6004F51 for 220VAC applications, respectively.
**C6-R9 is the snubber network:
C6
= 0.1uF, 200V,
R9
= 1k Ohm, 1/2W (115VAC);
C6
= 0.05uF, 400V,
R9
= 1k Ohm, 1W (220VAC)
6.
The values selected for R10, R11, and R12 will produce the
full dimming range. To reduce the maximum intensity,
increase the value of R12. To increase the minimum
intensity, increase the value of R10. Increasing either R10
or R12 will reduce the dimming range. R10 may have to be
increased for very low wattage loads.
D1 = 1N4148
Z = 5.6V, 1W (Zener)
T = Q4004L4 Typical Triac
(1)
*
T = Q5003L4 Typical Triac
(1)
L = 100µH (RFI Filter)
*
L = 200µH (RFI Filter)
(1)
For loads greater than 6A,
use an alternistor
NOTES
C1 = 0.15µF, 200V
*
C1 = 0.15µF, 400V
C2 = 0.22µF, 200V
*
C2 = 0.15µF, 400V
C3 = 0.002µF, 10V
*
Component change for 220VAC
**
Snubber Network (See Note 5)
C4 = 100µF, 10V
C5 = 0.1µF, 10V
C6 = 0.01uF, 10V
C7 = 0.1uF, 10V
R1 = 270Ω, 1/2W
R1 = 1kΩ, 1W
*
R2 = 680kΩ, 1/4W
*
R2 = 1.5MΩ, 1/4W
R3 = 1.5MΩ, 1/4W
R4 = 1MΩ to 5MΩ, 1/4W
(Select for Sensitivity)
R5, R6 = 2.7MΩ, 1/4W
*
R5, R6 = 4.7MΩ, 1/4W
R7 = 150kΩ, 1/4W
R8 = 62Ω, 1/4W
R10 = 33kΩ, 1/4W
R11 = 100kΩ Pot., 1/4W
R12 = 16kΩ, 1/4W
FIGURE 6.
EXT
10kΩ
ELECTRONIC EXTENSION
IN914
*R
*R
MPS8599
APPLICATION EXAMPLE:
A typical implementation of the light dimmer circuit is shown in Fig. 5.
Here the lamp is turned on and off by touching the touch plate.
The function of different components are as follows:
• The 5V DC supply for the chip is provided by Z, D1, R1, C2 and C4.
• R2 and C3 generate the filtered signal for the SYNC input
AC phase synchronization.
• R3 and C5 act as a filter circuit for the electronic extension.
If extensions are not used, the EXT input (Pin 6) should be
tied to Vss (Pin 7).
• R4, R5 and R6 set up the sensitivity of the SENS/ input.
• R8 provides current limiting and isolation between the chip
output and the triac gate.
• C1 and L are RFI filter circuits.
• R10, R11, R12 and C7 selects and adjusts the dimming level.
TOUCH PLATE
200kΩ
*R
= 2M W for 115VAC
*R
= 3.6M W for 220VAC
All Resistors 1/4W
P
EXTENSIONS:
All On / Off switching functions can be imple-
mented by utilizing the EXT input. Use a pushbutton or the
electronic switch in conjunction with a Touch Plate as shown
in Figure 6. When the plate is touched, a logic high level is
generated at the EXT input of the IC for both half-cycles of
the line frequency. (See Figure 5)
7642-101308-4
Talking
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