Sanyo LA7555 Specifications

Any and all SANYO products described or contained herein do not have specifications that can handle
applications that require extremely high levels of reliability, such as life-support systems, aircraft’s
control systems, or other applications whose failure can be reasonably expected to result in serious
physical and/or material damage. Consult with your SANYO representative nearest you before using
any SANYO products described or contained herein in such applications.

SANYO assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges,or other
parameters) listed in products specifications of any and all SANYO products described or contained
herein.

Monolithic Linear IC

IF Signal Processing (VIF+SIF)

Circuit for TV / VCR Use

Ordering number:ENN2927

LA7555

SANYO Electric Co.,Ltd. Semiconductor Company

TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, T aito-ku, TOKYO, 110-8534 JAPAN

Overview

The LA7555 is a full sync detection method VIF + SIF
monolithic linear IC using a PLL. It has excellent 920kHz
beat and buzz beat characteristics, making it ideal for use

in audio multiplexing and high-quality AV equipment.

Functions

• VIF section

· VIF amplifier · Video sync detecton · IF AGC

· B/W NC · RG AGC · AFT

· VCO · APC DET · Lock DET

• SIF section

· SIF limiter amplifer · FM quadrature detection

• Audio section

· DC attenuator · AF driver

• Muting

· Audio muting (pin 2)

· AFT defeat (pin 14)

· Audio-Video simultaneous muting (pin 10, 13)

Package Dimensions

unit:mm

3067A-DIP24S

[LA7555]

21.0

(0.71)

24

1

0.9

1.78

0.48

0.95

13

7.62

12

(3.25)

0.51min

SANYO : DIP24S

6.4

0.25

3.9max

3.3

Features

• 24-pin DIP shrink package being the smallest one used
for PLL ICs.

• Excellent 920kHz beat characteristics.

• Excellent buzz beat characteristics.

• High-gain VIF amplifier.

• High-speed AGC possible.

• Excellent power supply ripple characteristics.

Specifications

Maximum Ratings at Ta = 25˚C

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LA7555

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No.2927–2/11

LA7555

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Equivalent Circuit Block Diagram

No.2927–3/11

Precautions when using the LA7555

LA7555

Description of Operation

1. IF amplifier
As shown in Fig.1-1, the IF amplifier consists of three amplifiers directly connected with balanced input.
Amplifiers 1, 2 and 3, and the gain are controlled by the AGC.

Fig.1-1

No.2927–4/11

LA7555

2. Video detector
As shown in Fig.2-1, the video detector is a PLL-type. AM detection (video detection) is by phase shifting the IF
signal and VCO output signal 180° and multiplying the input signal. It offers excellent buzz and beat characteris­tics as detection is by multiplication by a clean signal. Also, excellent detection characteristics are obtained in the
same manner for the overmodulation signal.

Fig.2-1

3. Video amplifier B/W noise canceller
As shown in Fig.3-1, the video amplifier amplifies the detection output voltage over a wide band to the desired
voltage (=2.2Vp-p). The amplified video signal passes through the B/W noise canceller and is output to pin 21.
White : The noise canceller operates as shown in Fig.3-3 as the input of noise exceeding the white level of the

video signal as shown in Fig.3-2 will cause noticeable noise on the screen.

Black : The noise canceller operates as shown in Fig.3-3 as the input of noise exceeding the sync signal tip as

shown in Fig.3-2 will prevent proper operation of the next-stage sync separation circuit.

Fig.3-1

Fig.3-2 Fig.3-3

No.2927–5/11

LA7555

4. Lock detector
As shown in Fig.4-1, the lock detector is an APC time constant switching detection circuit which expands the APC
pull-in range. The detection circuit operates by the OR of the IF AGC voltage and the video signal. The weak field
is detected by the IF AGC voltage and the unlock state when detuned is detected from the video signal.

Fig.4-1

5. AGC detector
As shown in Fig.5-1, the AGC detector is equipped with a noise canceller function which prevents malfunction of
the AGC system. The AGC detection output (pin 13) is also used for video output, FM detection output, and as the
simultaneous mute (AV MUTE) pin.

Fig.5-1

6. RF AGC
As shown in Fig.6-1, the RF AGC controls the gain of the tuner’s RF amplifier. Measurement is made whether the
region is snow region (noise on the screen, poor S/N ratio) or a saturation region (contours can be clearly seen but
look bad due to video signal distortion), and the RF AGC delay point is set as shown in Fig6-2. Pin 10 is also used
for video output, FM detection output, and as the simultaneous mute (AV MUTE) pin.

Fig.6-1

Fig.6-2

No.2927–6/11

LA7555

7. AFT
As shown in Fig.7-1, the AFT is a balanced-type using a quadrature detection circuit. The input signal is shifted
90° by the internal capacitor and external phase shifter, and quadrature-detected. Pin 14 is also used as the AFT
Defeat pin. Fig.7-1

Fig.7-1

C2 forms a sound trap for preventing malfunction of the AFT.

8. SIF limiting amplifier
As shown in Fig.8-1, the SIF limiting amplifier is an unbalanced limiting amplifier consisting of four stages
derectly connected. There is negative feedback within the IC to balance the differential amplifier.

Fig.8-1

9. Quadrature detection
SIF quadrature detection is by the single pin detector with internal phase shift capacitor, shown in Fig.9-1. FM
detection is by shifting the SIF signal 90° and multiplying it. The characteristics of the phase shifting circuit are as
follows :

1. Demodulation output .....mainly Q

L

2. Distortion ... linearity of phase shifting circuit, symmetry of S curve.
The linearity of the phase shifting circuit can be improved by lowering QL and increasing the band with a single­tuned circuit, but the FM detection output will drop.
Pin 2 is also used as the SIF mute pin.

Fig.9-1

10.Electronic volume control
As shown in Fig.10-1, this is an electronic volume control, having a control pin with high input impedance. The
attenuation curve is a logarithmic curve. The external audio input impedance is approximately 30kΩ.

No.2927–7/11

LA7555

Fig.10-1

11.AF amplifier
As shown in Fig.11-1, this is an AF amplifier equipped with an NFB pin. An audio power amplifier can be easily
configured by use of this NFB pin. The gain of the power amplifier can be controlled by the ratio of R1 and R2.

Fig.11-1

VCO adjustment methods

The following two methods are available for adjusting the VCO.

1. APC voltage offset adjustment method

a. Connect a digital voltmeter to pin 20 (APC filter pin ) (Fig.1).
b. Lower the IF input level and connect the IF AGC (pin 13) to GND.

Measure the voltage on pin 20 at this time.

c. Raise the IF input level to the desired value. Free the IF AGC from GND (internal AGC). Adjust the VCO so

that the voltage (V2) on pin 20 is equal to V1.

Note : When adjusting by this method, use a DVM (digital voltme-

ter) with high input impedance. At Zi=10MΩ, the adjustment
error is approximately 20kHz, The error (∆V) with the DVM
connected is.

Fig.1

R

∆V (mV)= V (1– )

Z+R

1

1

The change in VCO free-running frequency (∆f) according to
∆V is ∆f (kHz)=∆V× β
where β=VCO control sensitivity (kHz/mV)

2. Direct reading method

a. Lower the IF input level and adjust the IF AGC (pin 13) to between GND and about 4V (VCO free run).
b. Monitor the carrier frequency leaking from pins other than the VCO coil, or pattern, chassis, and adjust the

VCO coil to obtain the desired frequency (fp).

No.2927–8/11

LA7555

Measurement of VIF selectivity characteristics

The pull-in range of the PLL-type VIF IC is approximately ±2MHz. Thus, it is not possible to measure the match­ing characteristics of the tuner SAW filter easily as with the dummy syncronization detection method. The follow­ing is just one example of how to measure the selectivity characteristics for a single signal.

Test Circuit

Conditions

1. Apply voltage to the IF AGC (pin 13) and adjust until the video output A is 0.5Vp-p.

2. Atteach a 4.7µF capacitor to the APC filter (pin 20) so that the PLL is unlocked.

3. The waveform shown in the diagr am below can be monitored through the externally mounted detector.

Note : Error will occur in the measurement of the selectivity characteristics if the video frequency changes between

A and C (by a video equalizer, etc.)

Externally Mounted Detector (Example)

(1) (2) Voltage doubler type

No.2927–9/11

Sample Application Circuit (JAPAN)

LA7555

Item

JAPAN
fP=58.75MHz

US
fP=45.75MHz

PAL
fP=38.9MHz

T1 : VCO coil T2 : AFT coil T3 : SIF coil

7mm square

0.12φ 6t
C=24pF PH
S-CORE
HW-6226-4

MITSUMI

7mm square

0.12φ 9t
C=24pF PH
S-CORE
HW-6227-4

MITSUMI

7mm square

0.12φ 11t
C=24pF PH
S-CORE
MA-6389

MITSUMI

7mm square

0.5φ 3 1/2t
External c=91pF
MA-6342

MITSUMI

7mm square

0.5φ 5 1/2t
External c=91pF
MA-6343

MITSUMI

7mm square

0.5φ 6 1/2t
External c=91pF
MA-7115

MITSUMI

7mm square

0.08φ
19t - 19t
C=100pF
KS-6102-1
MITSUMI

7mm square

0.08φ
19t - 19t
C=100pF
KS-6102-1
MITSUMI

SW filter

SAW Filter
TSF1110 SANYO

SAW Filter
TSF1203 SANYO
TSF1212 SANYO

SAW Filter
TSF1303 SANYO

No.2927–10/11

LA7555

Specifications of any and all SANYO products described or contained herein stipulate the performance,
characteristics, and functions of the described products in the independent state, and are not guarantees
of the performance, characteristics, and functions of the described products as mounted in the customer's
products or equipment. To verify symptoms and states that cannot be evaluated in an independent device,
the customer should always evaluate and test devices mounted in the customer's products or equipment.

SANYO Electric Co., Ltd. strives to supply high-quality high-reliability products. However, any and all
semiconductor products fail with some probability. It is possible that these probabilistic failures could
give rise to accidents or events that could endanger human lives, that could give rise to smoke or fire,
or that could cause damage to other property. When designing equipment, adopt safety measures so
that these kinds of accidents or events cannot occur. Such measures include but are not limited to protective
circuits and error prevention circuits for safe design, redundant design, and structural design.

In the event that any or all SANYO products(including technical data,services) described or
contained herein are controlled under any of applicable local export control laws and regulations,
such products must not be exported without obtaining the export license from the authorities
concerned in accordance with the above law.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying and recording, or any information storage or retrieval system,
or otherwise, without the prior written permission of SANYO Electric Co. , Ltd.

Any and all information described or contained herein are subject to change without notice due to
product/technology improvement, etc. When designing equipment, refer to the "Delivery Specification"
for the SANYO product that you intend to use.

Information (including circuit diagrams and circuit parameters) herein is for example only ; it is not
guaranteed for volume production. SANYO believes information herein is accurate and reliable, but
no guarantees are made or implied regarding its use or any infringements of intellectual property rights
or other rights of third parties.

This catalog provides information as of October, 2000. Specifications and information herein are subject
to change without notice.

PS No.2927–11/11