PCF1303T datasheet(4/10 Pages) PHILIPS

4 / 10 page

November 1986

Philips Semiconductors

Product speciﬁcation

18-element bar graph LCD driver

PCF1303T

FUNCTIONAL DESCRIPTION

The PCF1303T is an 18-element bar graph LCD driver with linear relation to the control voltage when in pointer or

thermometer mode.

The first segment will energize when the control voltage is less than the trigger voltage (VT(bar)2 see equation (3)).

The circuit has analogue and digital sections.

The analogue section consists of a comparator with the inverting input coupled to the input control voltage. The

non-inverting input of the comparator is connected via 17 analogue switches to the nodes of an 18-element resistor

divider. The extremities of the resistor divider are coupled via high-input impedance amplifiers to the maximum reference

voltage input and the minimum reference voltage input.

The control input functions with Schmitt trigger action.

The digital section has one reference output (QR) to drive the back-plane and 18 outputs (Q1 to Q18) to drive the

segments.

The segment outputs incorporate two latches and some gates.

The circuit is driven by an on-chip oscillator with external resistors and capacitors. The outputs are driven at typical

100 Hz.

LINEARITY

(1)

Vstep′ is the voltage drop (internal) across the resistor-ladder network.

∆Vstep is the differential on Vstep.

(2)

∆V

2 and ∆V2

′ are the maximum offset voltage spread of the on-chip voltage followers.

ABSOLUTE VOLTAGE TRIGGER LEVEL

The absolute voltage trigger level at the Vc pin is VT(bar)n;

(3)

n = number of segments; 2

≤ n ≤ 18.

∆V

R is the voltage deviation at step n of the resistor-ladder network (for n = 2 or 18, ∆VR = ∆Vstep).

∆V1 is the offset voltage for the on-chip comparator.

VH is the hysteresis voltage: 30% Vstep ≥ VH ≥ 10% Vstep.

Note to equation (3)

For

∆V2 the same sign (+ or −) should be used as in equation (2).

step

′ ∆Vstep

step

′

ref max

∆V

′

()

ref min

∆V

()

–

---------------------------------------------------------------------------------------------

T bar

() n

ref min

∆V

()

–

() V

step

′

∆V

{} ∆V

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