LSI/CSI
UL
®
LS7232NT
(631) 271-0400 FAX (631) 271-0405
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747
A3800
PROXIMITY/TOUCH CONTROL HALOGEN LAMP DIMMER
FEATURES:
• Control of incandescent and transformer coupled
halogen lamps.
• No-Touch lamp control through optical sensing
• PLL synchronization of AC for wall switch application.
• Extension input for remote control
• Safety-shutdown for transformer malfunction.
• Pin-selectable operating modes
• Single 5V power supply
• 50Hz/60Hz AC line frequency
• LS7232NT (DIP), LS7232NT-S (SOIC) - See Figure 1
DESCRIPTION:
LS7232NT is a CMOS integrated circuit designed for brightness
control of incandescent lamps or tranformer coupled low voltage
halogen lamps. The brightness is controlled by controlling the fir-
ing angle of a triac in series with the lamp and triggered by the
LS7232NT. A Phase-Locked-Loop keeps the LS7232NT phase
pointer locked in phase with the line voltage.
A unique optical user interface provides for a smooth control of
the lamp intensity without the need for touching any sensor
plate. A mechanical switch interface for dimming control is also
provided which can be used for a remote touch plate. The IC in-
cludes features to address problems associated with inductive
loads such as transformers in low voltage halogen lamp applica-
tion. The voltage to current phase lag resulting from the in-
ductance may prevent the triac from shutting off at AC zero
crossover and/or prevent the triac from maintaining conduction
following the removal of the gate trigger.
These problems are addressed by the LS7232NT in the fol-
lowing manner:
1. Compensation for delayed triac cut-off.
When trigger pulse is due to occur at a conduction angle
which coincides with the on-state of the triac, the trigger
pulse is delayed until the triac has turned off. This elim-
inates the underlying cause of half-waving.
2. Compensation for delayed triac turn-on.
At the set conduction angle, a triac trigger pulse of 130.2µs
(60Hz) is issued by the dimmer IC. If the triac fails to fire, a
second trigger pulse of 260.4µs width is issued a milli-
second later as a second attempt to fire the triac during the
same half-cycle.
3. Safety-Shutdown.
If the frequency of occurrences of the delayed cut-off and
the delayed turn-on exceeds a preset threshold, a shut-
down is initiated by turning off the triac trigger pulses. The
safety-shutdown threshold value is accumulated in a 4-bit
Up/Down counter. The count increments for every oc-
currence of delayed cut-off or delayed turn-on and decre-
ments once every 8 SYNC pulses (AC line cycles). The
count will not decrement below zero. If the count reaches
15, the safety-shut-down is effected.
November 2001
PIN ASSIGNMENT - TOP VIEW
CAP
SYNC
ANODE
1
2
3
LS7232NT
14
13
12
11
10
9
8
V
DD
(+V)
M2
M1
RC
LEDO
TRIG/
Vss (-V)
CATHODE 4
PHOTOUT 5
SENS
6
REMOTE 7
FIGURE 1
The LS7232NT can be configured in 7 different modes of dim-
ming and timing off functions selected by two 3-state mode
pins.
INPUT/OUTPUT DESCRIPTION:
CAP
(Pin 1)
PLL filter capacitor input. A 0.02µF capacitor is required at this
input for the optimal operation of the PLL.
SYNC
(Pin 2)
The phase pointer for the triac trigger signal is synchronized
with the 50Hz/60Hz AC voltage applied at the SYNC input by
the internal PLL. The triac On/Off status information is also de-
rived from this input.
ANODE
(Pin 3)
CATHODE
(Pin 4) and
PHOTOUT
(Pin 5)
These three pins constitute the input/outputs of a trans-
conductance and voltage amplifier pair (See Fig. 6) for con-
verting the current from a photo-diode to a voltage stimulus for
application at the SENS input. The photo-signal is used in lieu
of a touch plate for a touchless dimmer system. The output at
PHOTOUT is governed by the following equation:
V
OUT
= V
DD
/2 + 2I
D
R
f
Where V
DD
= Supply Voltage
I
D
= Current in Photo-diode connected between
ANODE and CATHODE
R
f
= Feedback resistance between PHOTOUT
and CATHODE
A potentiometer is used for R
f
for controlling the sensitivity of
the photo-amplifier system.
7232NT-111501-1
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