
TABLE 1
TOUCH TYPE
SHORT (T
S1
 Duration)                                                      LONG (T
S2
 Duration)
PRE-TOUCH              POST-TOUCH               PRE-TOUCH              POST-TOUCH 
                                                                                                       
               Off                           Max                                      Off                     Starts varying at Min
               Max                           Off                                      Max                    Starts varying at Max
                 Intermediate                    Off                               Intermediate              Starts varying at
                                                                                                                               Pre-Touch brightness 
                        Off                        Memory                                   Off                     Starts varying at
                                       (Note 1)                                                              Memory (Note 2)
               Max                           Off                                      Max                    Starts varying at Max
                 Intermediate                    Off                               Intermediate              Starts varying at
                                                                                                                               Pre-Touch brightness
               Off                           Max                                      Off                     Starts varying at Min
               Max                           Off                                      Max                    Starts varying at Max
                 Intermediate                    Off                               Intermediate              Starts varying at
                                                                                                                               Pre-Touch brightness 
                        Off                        Memory                                   Off                     Starts varying at
                                      (Note 1)                                                              Memory (Note 2)
               Max                           Off                                      Max                    Starts varying at Max
                 Intermediate                    Off                               Intermediate              Starts varying at
                                                                                                                               Pre-Touch brightness 
                 the Memory value defaults to maximum conduction angle.
NOTE 2:  
First time after power-up, LONG touch causes intensity to vary starting at minimum conduction angle.
NOTE 3
:  NO = Dimming direction  does not reverse from prior dimming direction.
                YES = Dimming direction does reverse from prior dimming direction.
                N/A = Does not apply
SYNC
 (Pin 4)
The AC Line Frequency is applied to this input through an
external RC circuit (See Figure 5).  The Phase-Lock Loop
in the IC synchronizes all internal timings to the AC signal
at the SYNC input.
SENS 
(Pin 5)
A low level activates this input (See Table 1) which con-
trols the turn-on, turn-off and conduction angle  (See-
Figure 3) of the TRIG signal with respect to the SYNC in-
put.
EXT
 (Pin 6)
The EXT input is functionally identical to the SENS input
except that a high level activates this input. It is rec-
ommended that the EXT input be used instead of the
SENS input when long extension wires are employed be-
tween the IC and the Sensing Circuitry (See Figure 5 and
Figure 6) because the EXT input is less susceptible to
“Noise”.
V
DD
(Pin 4)
Supply voltage negative terminal.
TRIG 
(Pin 8)
The TRIG output is a low level pulse occurring once every
half-cycle of the SYNC input. The conduction angle, , of the
output in relation to the SYNC signal controls the lamp bright-
ness.
In continuous dimming operation (i.e. when the SENS input is
continuously held low) the TRIG conduction angle, , sweeps
up and down between 41 and 158 continuously. The time vs
 curve is not linear  (See Figure 2). Between two maxima on
this curve, there are 4 discontinuous points labeled A1, B1,
B2, A2. The discontinuities are as follows:
1. From maximum to A1. In this region,  is changed by
        equal increments (
) for every 2 SYNC clocks.
2. From A1 to B1. In this region, the increments (
) take
        place for every 4 SYNC clocks.
3. From B1 to B2. In this region  is held at a constant 
 level (
 = 0).
4. From B2 to A2. Same as 2.
5. From A2 to Max. Same as 1.
The slower rate of change in  over A1B1B2A2 region is to
accommodate for eye adjustment at lower light intensity.
The functional differences of different versions of the light dimmer ICs are explained in Table 1 and the TRIG
output conduction angle diagrams in Figure 2.
PART
NUMBER
LS7231
LS7232
LS7233
LS7234
DIMMING
DIRECTION
REVERSAL
(Note 3)
N/A
N/A
NO
YES
N/A
YES
N/A
N/A
YES
NO
N/A
NO
NOTE 1
:  "Memory" refers to the conduction angle,  which existed prior to the current off-state.  First time after power-up,
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