L6452(1999) Просмотр технического описания (PDF) - STMicroelectronics

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L6452
(Rev.:1999)

DUAL 13X16 MATRIX HEAD INK JET DRIVER

STMicroelectronics 

L6452

PRINT HEAD TEMPERATURE CONTROL PART

Introduction

For quality printing, it is necessary to know and

control the temperature of the printhead. Thus,

the latter has a built - in aluminium resistor,

whose value changes slightly with the tempera-

ture. The temperature determination is done by

injecting a constant current in the resistor, and

measuring the voltage drop across it. Since high -

end printers have two heads, it must also be pos-

sible to switch quikly the measurement process

from one to the other. The function is foreseen to

be integrated into the head driver, and is de-

scribed hereafter.

Print Head Block Diagram (fig. 4)

At first we have a constant current source, which

can be disabled by an external pin (ONenable) or

by a control register, described later. The value of

the current can be programmed by an external

resistor, and is given by:

ICCS

=

Vref ⋅4

2 ⋅ Rext

This current is injected either into the aluminium

resistor of the head A (Ralu. A) or B (Ralu. B), de-

pending of the switch SW3. The alu. resistors are

grounded, and the voltage at their << hot >> side

Figure 4. Print Head Block Diagram

(Vx) is re-entered via the pins Vxa and Vxb. Us-

ing separate pins from Rxa and Rxb permits to be

more flexible, and a filter can eventually be added

as shown in the drawing.

The voltage Vx is amplified by A1 and A2, and

then converted in a digital value. To be compat-

ible with the input range of the A/D converter, it is

necessary to subtract an offset voltage Voffset

from Vx. Moreover, as the initial value of the alu.

resistor is very unprecise. Voffset must be adjust-

able; this is done by means of a 5 bit - D/A con-

verter, giving 32 different values. Finally, the volt-

age at the input of the A/D converter is:

VCH0 = g1 ⋅ g2 ⋅ VX - g2 ⋅ VOFFSET

or

VCH0 = g1 ⋅ g2 ⋅ Ralu ⋅ ICCS - g2 ⋅ VOFFSET;

VOFFSET = VREF/2 + N ⋅ VREF/32 N = 0, 1, ...31

The reference voltage generator (VREF) is inte-

grated, and used for the current source and both

the A/D and D/A converters. In this way, the sys-

tem performance is independent from the preci-

sion of VREF; this one should, however, be stable.

Vref is also available on pin #45, and can be

used for low consumption purposes. (The exter-

nal sinked current has to be a DC current)

The system is under control of a 10 bit register,

CR. CR is accessed serially and has a transpar-

ent latch, which can be used or not (by trying the

latch signal CR latch to VCC).

Va

VREF OUT

REXT

ONENABLE

REF

VOLT

VREF

HIGH-SIDE

CONSTANT

CURRENT Vx

SOURCE

SW1

SW2

SW3

A1

g1

VREF/2

VOFFSET

+

A2

+

CH0

g2

-

VREF

D/A 5 BIT

VREF

A

D

A

B

D

C

CONV START

ADCK

ADDATA

CH5

CH4

CH3

CH2

CH1

A/D

INPUTS

CH0_BUF

RXA, RXB

A/B ON/OFF DA4 DA3 DA2 DA1 DA0 S2

LATCH 10 BIT

SHIFT REG. 10 BIT

S1 S0

CRLATCH

CRCLOCK

CRDATA

CONTROL

REGISTER

VXA, VXB

ANALOG GND

10/16

RALU A

RALU B

Note; the analog ground is separated from the digital ground of the remaining part of the driver

D97IN533B

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