TRIG

OUTPUT

DRIVER

DIGITAL

COM-

PARATOR

BRIGHTNESS

MEMORY

Ø

POINTER

PHASE

LOCK

LOOP

CONTROL

LOGIC

BUF

BUF

BUF

BUF

SYNC

CAP

DOZE

DOWN

UP

(+V)

(-V)

FIGURE 4

LS7534/LS7535 BLOCK DIAGRAM

4

3

2

6

5

1

7

8

APPLICATION EXAMPLES:

Typical dimmer light switch circuit schematics are shown in Fig. 5A (LS7534) and

Fig. 5B (LS7535). The brightness of the lamp is set by touching the UP and DOWN

touch plates in Fig. 5A and closure of the UP and DOWN switches in Fig. 5B. The

functions of different components are as follows:

• Z, D1, R1, C2 and C5 produce the 15V DC supply for the chip.

• R2 and C4 filter and current limit the AC signal for the SYNC input.

• C3 is the filter capacitor for the internal PLL.

• C1 and L are RFI filters.

• In Fig. 5A, R3 and R4 set the touch sensitivity of the UP and DOWN inputs.

• In Fig. 5B, R3 limits the current between Vss and the UP and DOWN inputs upon

closure of a switch.

• The resistor and diode connected between the chip output and the triac gate

provides current limiting and isolation for the chip. The resistor is R5 in Fig. 5A

and R4 in Fig. 5B.

• In Fig. 5B, PCB layout may cause triac switching transients to be coupled to the Up

or Down input which can have the effect of having a Long switch closure “lock-up”

at a certain phase angle output. In this case, capacitors C6 and C7 must be added

as shown.

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.

7535-012703-5