LS7232NT

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


Pinout




Specifications

PARAMETER	SYMBOL	VALUE	UNIT
DC Supply Voltage	VDD - VSS	+7	V
Any Input Voltage	VIN	VSS -.3 to VDD +.3	V
Operating temperature	TA	0 to +90
Storage temperature	TSTG	-65 to +150

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 firing 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 includes features to address problems associated with inductive loads such as transformers in low voltage halogen lamp application.

`The voltage to current phase lag resulting from the inductance 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 following 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 eliminates the underlying cause of half-waving.

`2. Compensation for delayed triac turn-on.
At the set conduction angle, a triac trigger pulse of 130.2s (60Hz) is issued by the dimmer IC. If the triac fails to fire, a second trigger pulse of 260.4s width is issued a millisecond 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 shutdown 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 occurrence of delayed cut-off or delayed turn-on and decrements 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.The LS7232NT can be configured in 7 different modes of dimming and timing off functions selected by two 3-state mode pins.