TEA2028 datasheet(18/47 Pages) STMICROELECTRONICS

18 / 47 page

V.4 - Line saw-tooth generator

Before going through a detailed study of the second

phase locked loop ”

φ2”, let’s have an overview of

the linesaw-tooth generator which has been mainly

implemented for

φ2 phase variations and also the

phase modulation of the switching power supply.

It uses the combination of an external capacitor

connected to Pin 13 and an internally implemented

constant current generatorto generatea saw-tooth

voltage at line frequency.

Its frequency is determined by the reset frequency

of the capacitor ”C13”. This reset signal is issued

by the line logic circuitry at a period multiple of VCO

period (

×32).

-IC =K

⋅ IR =K ⋅

1.26

R14

= 200

µA

-V13PP =

(TH − treset)

C13

⋅ 1.26(TH − treset)

R14

⋅ C13

= 3.48V

-VCE(SAT)T1

≈ 20mV ⇒ V13(MAX) = 3.5V

- In sync mode :

TH =64

µs, tRESET = 6.5µs, K = 0.527 ± 2%

R14

3.32k

Ω

C13

3.3nF

Constant

1.26V

Reset

ϕ2

and SMPS

Reset

6.5

µs

V13

VPP

3.5

Figure 34

0.3

µs

2.35

µs 2.35µs

5.8

µs

6.5

µs

Inhibit ion

LINE SYNC .

ϕ1SIGNAL

VIDEO

ON PIN 27

LINE

INHIBITI ON

Figure 32

100

µA

(short)

500

µA

(Long)

ϕ1

Line Sync.

Phase Comparator (

ϕ1)

SINH(S)

INH(L)

≥ 1

Video Recognition

Mute

FRI

Line Inhibition

BLK

VCR

Figure 33 :

ϕ1 Inhibition Logic Block Diagram

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