ST7554 Ver la hoja de datos (PDF) - STMicroelectronics
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ST7554 Datasheet PDF : 11 Pages
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ST7554
PIN DESCRIPTION (continued)
3 - Reset, Powerdown (RESET, PDOWN)
RESET Pin initialises the internal counters and
control registers to their default value. A minimum
low pulse of 1ms is required to reset the chip.
In a typical application RESET is connected to
VBUS through a R, C network. This ensures that
the chip is reset at each connection / disconnection
to the USB bus (see Figure 3).
PDOWN Pin shall be connected to the powerdown
inputs of the external codec used on the SSI.
When ST7554 is in Suspend mode, PDOWN is
forced low so that the external codec is in
powerdown.
Figure 3 : RC network for RESET
VBUS
R
220kW
C
10nF
12 RESET
4 - Serial Synchronous Interface
ST7554 has a Serial Syncronous Interface (SSI)
dedicated to the connection of the STLC7550 or
ST75951, ST high performance Modem Analog
Front-End (MAFE).
4.1 - Data (DIN, DOUT)
Digital data word input/output of SSI, to be con-
nected to the data word pins of STLC7550 or
ST75951.
4.2 - Master Clock (MCLK)
This pin is the master clock output.
4.3 - Frame Synchronization (FS)
The frame synchronization is used to synchronize data
transfer between ST7554 and the external Codec.
4.4 - Hardware Control (HC1)
HC1 must be connected to the corresponding pin of
STLC7550 or ST75951, while their HC0 Pin shall be
tied to the 3.3V VREGD digital supply. This pin
selects data or control modes for the Modem Codec.
4.5 - DAA Selection (DAASEL)
Connect to VREGD when using silicon DAA chipset
based on ST75951 + ST952. Connect to DGND
when using STLC7550 with discrete interface.
5 - DAA Control Pins (IMP, DC, BUZEN,
PULSE, DISHS, RFC, LED, CLID, HO, HSDT, RI)
These pins control the World Wide software
programmable DAA through ST75951/ST952.
6 - Crystal (XTALIN, XTALOUT)
These pins must be tied to the 9.216MHz external
crystal.
It is recommended to use a ±50ppm fundamental
parallel resonator crystal. It is recommended to
insert a 1.8kΩ resistor between XTALOUT and the
crystal to limit its energy to 100µW for a 20Ω
resonator (see Figure 4).
For a SMD crystal the load capacitor is typically
CLOAD = 12pF and this leads to an ideal value of
C = 24pF for the capacitors between the crystal
and analog ground (AGND). Anyway, in practice
these capacitors shall be reduced down to
C = 18pF each by considering parasitic capacitors
on PCB and package (see Figure 4).
After a reset or when leaving the suspend state,
the 9.216MHz is asserted inside ST7554 only
3.5ms later in order to wait for it to be stable.
Figure 4 : Application schematic for the
9.216MHz external crystal
XTAL
IN
9
XTAL
OUT
10
R
1.8kW
C
18pF
C
18pF
AGND AGND
7 - PLL Output Filter (FLTPLL)
This pin must be connected to the analog ground
(AGND) through a 33pF capacitor.
8 - Reserved Pins (18 pins)
These pins must be left not connected except
Pin 47 which should be connected to the digital
ground DGND.
5/11
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