TDA9105 datasheet(22/32 Pages) STMICROELECTRONICS

22 / 32 page

OPERATING DESCRIPTION (continued)

VERTICAL PART (continued)

Function

When the synchronisation pulse is not present, an

internal current source sets the free running fre-

quency. For an external capacitor, COSC = 150nF,

the typical free running frequency is 100Hz.

Typical free running frequency can be calculated

by :

(Hz)= 1.5 ⋅ 10−5 ⋅

COSC

(nF)

A negative or positive TTL level pulse applied on

Pin 34 (VSYNC) can synchronise the ramp in the

frequency range [fmin, fmax]. This frequency range

depends on the external capacitor connected on

Pin 27. A capacitor in the range [150nF, 220nF] is

recommanded for application in the following

range : 50Hz to 120Hz.

Typical maximum and minimum frequency, at 25

°C

and without any correction (S correction or C cor-

rection), can be calculated by :

fmax = 2.5

⋅ f0 and fmin = 0.33 ⋅ f0

If S or C corrections are applied, these values are

slighty affected.

If an external synchronisation pulse is applied, the

internal oscillator is automaticaly caught but the

amplitude is no more constant. An internal correc-

tion is activated to adjust it in less than half a

second: the highest voltage of the ramp on Pin 27

is sampled on the sampling capacitor connected on

Pin 25 (VAGCCAP) at each clock pulse and a

transconductance amplifier generates the charge

current of the capacitor. The ramp amplitude be-

comes again constant.

It is recommanded to use a AGC capacitor with low

leakage current. A value lower than 100nA is man-

datory.

Pin 36, Vfly is the vertical flyback input used to

generate the composite blanking signal. If Vfly is

not used, (VREF - 0.5), at minimum, must be con-

nected to this input.

DC Control Adjustments

Then, S and C correction shapes can be added to

this ramp. This frequency independent S and C

corrections are generated internally; their ampli-

tude are DC adjustable on Pin 28 (VSAMP) and

Pin 29 (COR-C).

S correction is non effective for VSAMP lower than

VREF/4 and maximum for VSAMP = 3/4

⋅ VREF.

C correction is non effective for COR-C grounded

and maximum for :

COR-C = VREF/4 or COR-C = 3/4

⋅ VREF.

Endly, the amplitude of this S and C corrected ramp

can be adjusted by the voltage applied on Pin 31

(VAMP). The adjusted ramp is available on Pin 30

(VOUT) to drive an external power stage. The gain

of this stage is typically

±30% when voltage applied

on Pin 31 is in the range VREF/4 to 3/4

⋅ VREF.The

DC value of this ramp is kept constant in the

frequency range , for any correction applied on it.

Its typical value is : VDCOUT =VMID = 7/16

⋅ VREF.

A DC voltage is available on Pin 32 (VDCOUT). It is

driven by the voltage applied on Pin 33 (VPOS)

For a voltage control range between VREF/4 and

3/4

⋅ VREF, the voltage available on Pin 32 is :

VDCOUT = 7/16

⋅ VREF ± 300mV.

So, the VDCOUT voltage is correlated with DC value

of VOUT. It increases the accuracy when tempera-

ture varies.

Basic Equations

In first approximation, the amplitude of the ramp on

Pin 30 (VOUT)is :

VOUT -VMID =(VCAP -VMID) [1 + 0.16

⋅ (VAMP -VREF/2)]

with VMID = 7/16

⋅ VREF ; typically 3.5V

VMID is the middle value of the ramp on Pin 27

VCAP =V27 , ramp with fixed amplitude.

On Pin 32 (VDCOUT), the voltage (in volts) is calcu-

lated by : VDCOUT =VMID + 0.16

⋅ (VPOS -VREF/2).

VPOS is the voltage applied on Pin 33.

The current available on Pin 27

(when VSAMP =VREF/4) is :

IOSC = 3/8

⋅ VREF ⋅ COSC ⋅ f

COSC : capacitor connected on Pin 27

f synchronisation frequency

The recommanded capacitor value on Pin 25

(VAGC) is 470nF. Its ensures a good stability of the

internal closed loop.

TDA9105

22/32

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