TDA9875AH Philips Semiconductors, TDA9875AH Datasheet - Page 12

• Manufacturer Part Number: TDA9875AH
• Description: Digital TV Sound Processor DTVSP
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6.1.8
This function is enabled by setting bit AMUTE to logic 0
(see Section 10.3.11).
Upper and lower error limits may be defined by writing
appropriate values to two registers in the I
(see Sections 10.3.13 and 10.3.14). When the number of
errors in a 128 ms period exceeds the upper error limit the
auto-mute function will switch the output sound from
NICAM to whatever sound is on the first sound carrier
(FM or AM). When the error count is smaller than the lower
error limit the NICAM sound is restored.
The auto-mute function can be disabled by setting
bit AMUTE to logic 1. In this condition clicks become
audible when the error count increases; the user will hear
a signal of degrading quality.
A decision to enable/disable the auto-muting is taken by
the microcontroller based on an interpretation of the
application control bits C1, C2, C3 and C4 and, possibly,
any additional strategy implemented by the set maker in
the microcontroller software.
For NICAM L applications, it is recommended to
demodulate AM sound in the first sound IF and connect
the audio signal to the mono input of the TDA9875A.
By setting bit AMSEL (see Section 10.3.11), the
auto-mute function will switch to the audio ADC instead of
switching to the first sound carrier. The ADC source
selector (see Section 10.3.20) should be set to mono
input, where the AM sound signal should be connected.
6.1.9
The circuitry of the crystal oscillator is fully integrated, only
the external 24.576 MHz crystal is needed (see Fig.10).
6.1.10
Test pins TEST1 and TEST2 are active HIGH and in the
normal operating mode of the device they are connected
to V
and are not available to customers. Without external
circuitry these pins are pulled down to a LOW level with
internal resistors.
6.1.11
The power fail detector monitors the internal power supply
for the digital part of the device. If the supply has
temporarily been lower than the specified lower limit, the
Power-on reset bit POR (see Section 10.4.1), will be set to
logic 1.
1999 Dec 20
Digital TV Sound Processor (DTVSP)
SSD1
. Test functions are for manufacturing tests only
NICAM
C
T
P
EST PINS
OWER FAIL DETECTOR
RYSTAL OSCILLATOR
AUTO
-
MUTE
2
C-bus section
12
Bit CLRPOR (see Section 10.3.2) resets the Power-on
reset flip-flop to LOW. If this is detected, an initialization of
the TDA9875A has to be carried out to ensure reliable
operation.
6.1.12
The reset is active LOW. In order to perform a reset at
power-up, a simple RC circuit may be used which consists
of the integrated passive pull-up resistor and an external
capacitor connected to ground. The pull-up resistor has a
nominal value of 50 k , which can easily be measured
between pins CRESET and V
voltage has reached a certain minimum, the state of the
circuit is completely undefined, and it remains in this
undefined state unless a reset is applied.
The reset is guaranteed to be active when:
The required capacitor value depends on the gradient of
the rising power supply voltage. The time constant of the
RC circuit should be clearly larger than the rise time of the
power supply, to make sure that the reset condition is
always satisfied (see Fig.4), even considering the
tolerance spread. To avoid problems with a too slow
discharging of the capacitor at power-down, it may be
helpful to add a diode from pin CRESET to V
be noted that the internal ESD protection diode does not
help here as it only conducts at higher voltages. Under
difficult power supply conditions (e.g. very slow or
non-monotonic ramp-up), it is recommended to drive the
reset line from a microcontroller port or the like.
handbook, halfpage
The power supply is within the specified limits
(4.75 and 5.5 V)
The crystal oscillator is functioning
The voltage at pin CRESET is below 0.3V
V
DDD
voltage
(V)
= 5.0 V, typically below 1.8 V).
P
1.5
OWER
5
-
Fig.4 Reset at power-on.
ON RESET
V DDD
4.75 V
DDD2
reset active
guaranteed
V CRESET
. Before the supply
Product specification
TDA9875A
0.3V DDD
DDD
DDD
MHB595
t
. It should
(1.5 V if