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
TABLE 1
TOUCH TYPE
SHORT (T
S1
Duration)
PRE-TOUCH
Ø
Off
Max
Intermediate
POST-TOUCH
Ø
Max
Off
Off
LONG (T
S2
Duration)
PRE-TOUCH
Ø
Off
Max
Intermediate
POST-TOUCH
Ø
Starts varying at Min
Starts varying at Max
Starts varying at
Pre-Touch brightness
Starts varying at
Memory (Note 2)
Starts varying at Max
Starts varying at
Pre-Touch brightness
Starts varying at Min
Starts varying at Max
Starts varying at
Pre-Touch brightness
Starts varying at
Memory (Note 2)
Starts varying at Max
Starts varying at
Pre-Touch brightness
DIMMING
DIRECTION
REVERSAL
(Note 3)
LS7231
N/A
N/A
NO
LS7232
Off
Max
Intermediate
Memory
(Note 1)
Off
Off
Off
Max
Intermediate
YES
N/A
YES
LS7233
Off
Max
Intermediate
Max
Off
Off
Off
Max
Intermediate
N/A
N/A
YES
LS7234
Off
Max
Intermediate
Memory
(Note 1)
Off
Off
Off
Max
Intermediate
NO
N/A
NO
NOTE 1:
"Memory" refers to the conduction angle, Ø which existed prior to the current off-state. First time after power-up,
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 Ø (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.
7231-34-033195-2
TRIG
(Pin 8)
The TRIG output is a low level pulse occurring once every
half-cycle of the SYNC input. The conduction angle, Ø, 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, Ø, sweeps
up and down between 41˚ and 158˚ continuously. The time vs
Ø 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, Ø is changed by
equal increments (∆ø) for every 2 SYNC clocks.
2. From A1 to B1. In this region, the increments (∆ø) take
place for every 4 SYNC clocks.
3. From B1 to B2. In this region Ø is held at a constant
level (∆ø = 0).
4. From B2 to A2. Same as 2.
5. From A2 to Max. Same as 1.
The slower rate of change in ø over A1B1B2A2 region is to
accommodate for eye adjustment at lower light intensity.
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