Functional Description The OTL-444A is an IC designed to drive up to 64 LED's with a common cathode from a serial digital interface. Package Outline Drawing in PDF Format The electrical organization is shown here. Four binary bits at a time are directed into four separate 64 bit shift registers. When the 4x64 bits have been received, a latch signal transfers the content of the 4 shift registers into 4 latch registers allowing new data to enter the shift registers while the content of the latch registers is being used to control the LED's. The four shift registers are bidirectional to provide additional flexibility.

The 64 latched groups of 4 bits each define brightness of 64 LED's to provide grey scale or uniformity correction. The grey scale is achieved by producing LED drive pulse widths proportional to each latched 4 bit number. This digital to time analog conversion is accomplished by comparing the 64 latched groups of 4 bits each against a 4 bit binary counter which runs during the latch interval. An LED will be on as long as the output of the time base counter B is less than the latched 4 bit binary number Q defining the brightness of that LED.

This digital to time analog conversion is illustrated here.

In addition to the digital functions described above, the chip contains current sources maintaining a constant peak current I_p during the LED on time. The constant peak current for the 64 LED's is externally selectable in the range 1mA to 10mA using a control voltage V_c. The scale factor k is selectable and is illustrated here for 2/3mA per volt with the control voltage V_c ranging from 0 to +15 volts I_p = k V_c. A timing diagram is shown here.

---

SPECIFICATION          SUMMARY                   444A	Supply Voltage:	5V ± 0.5V
	Each Current Source:	0 to 10mA
	Operating Temperature:	-55 C to +85 C
	Storage Temperature:	-55 C to +125 C
	Max. Clock Rate:	8 MHz
	Logic Levels:	0 V and +5V
	Chip Size and Bonding Pad Identifications:	See ED-61190 (fig. 5)

---

Fig.1

Fig.2 Fig.3

Fig.4

---