HTCSEMI HT3914ANZ

The HT3914A is a monolithic integrated circuit that as senses analog voltage levels and drives 10 LED providing a linear analog display. A single pin changes the display from a moving dot to a bar graph. Current drive to the LEDs is regulated and programmable, eliminating the need for resistors. This feature is one that allows operation of the whole system from less than 3V.

The circuit contains its own adjustable reference and accurate 10-step voltage divider. The low-bias-current input buffer accepts signals down to ground, or V-, yet needs no protection against inputs of 35V above or below ground. The buffer drives 10 individual comparators referenced to the precision divider. Indication non-linearity can thus be held typically to 1/2%, even over a wide temperature range.

Versatility was designed into the HT3914A so that controller, visual alarm, and expanded scale functions are easily added on to the display system. The circuit can drive LEDs of many colors, or low-current incandescent lamps. Many HT3914A can be “chained” to form displays of 20 to over 100 segments. Both ends of the voltage divider are externally available so that 2 drivers can be made into a zero-center meter.

The HT3914A is very easy to apply as an analog meter circuit. A 1.2V full-scale meter requires only 1 resistor and a single 3V to 15V supply in addition to the 10 display LEDs. If the 1 resistor is a pot, it becomes the LED brightness control. The simplified block diagram illustrates this extremely simple external circuitry. When in the dot mode, there is a small amount of overlap or “fade” (about 1 mV*) between segments. This assures that at no time will all LEDs be “OFF”, thus any ambiguous display is avoided. Various novel displays are possible.

Much of the display flexibility derives from the fact that all outputs are individual, DC regulated currents. Various effects can be achieved by modulating these currents. The individual outputs can drive a transistor well as a LED at the same time, so controller functions including “staging” control can be performed. The HT3914A can also act as a programmer, or sequencer.

HT3914A is rated for operation from 0°C to +70°C. The HT3914A is available in an 18-lead PDIP (NFK) package.

• Drives LEDs, LCDs or Vacuum Fluorescents
• Bar or Dot Display Mode Externally Selectable by User
• Expandable to Displays of 100 Steps
• Internal Voltage Reference from 1.2V to 12V
• Operates with Single Supply of Less than 3V
• Inputs Operate Down to Ground
• Output Current Programmable from 2 mA to 30 mA
• No Multiplex Switching or Interaction Between Outputs
• Input Withstands ±35V without Damage or False Outputs
• LED Driver Outputs are Current Regulated, Open-collectors
• Outputs can Interface with TTL or CMOS Logic
• The Internal 10-step Divider is Floating and can be Referenced to a Wide Range of Voltages