SC7106/7107

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.2

2006.02.27

Http: www.silan.com.cn

Page 10 of 22

FIGURE 5. SIMPLE INVERTER FOR FIXED

DECIMAL POINT

FIGURE 6. EXCLUSIVE 'OR' GATE FOR DECIMAL

POINT DRIVE

The second function is a "lamp test". When TEST is pulled high (to V+) all segments will be turned on and the

display should read "1888". The TEST pin will sink about 15mA under these conditions.

NOTE: In the lamp test mode, the segments have a constant DC voltage (no square-wave). This may burn the

LCD display if maintained for extended periods.

9.DIGITAL SECTION

Figures 7 and 8 show the digital section for the SC7106 and SC7107, respectively. In the SC7106, an internal

digital ground is generated from a 6V Zener diode and a large P-Channel source follower. This supply is made

stiff to absorb the relative large capacitive currents when the back plane (BP) voltage is switched. The BP

frequency is the clock frequency divided by 800. For three readings/sec., this is a 60Hz square wave with a

nominal amplitude of 5V. The segments are driven at the same frequency and amplitude and are in phase with

BP when OFF, but out of phase when ON. In all cases negligible DC voltage exists across the segments.

Figures 8 is the Digital Section of the SC7107. It is identical to the SC7106 except that the regulated supply

and back plane drive have been eliminated and the segment drive has been increased from 2mA to 8mA, typical

for instrument size common anode LED displays. Since the 1000 output (pin 19) must sink current from two LED

segments it has twice the drive capability or 16mA.

In both devices, the polarity indication is "on" for negative analog inputs. If IN LO and IN HI are reversed, this

indication can be reversed also, if desired.