ATA5279 ATMEL Corporation, ATA5279 Datasheet - Page 26

• Manufacturer Part Number: ATA5279
• Manufacturer: ATMEL Corporation

3.10
3.11
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Oscillator
Internal Supply
ATA5279 [Preliminary]
This block provides the clock signals internally needed for control logic, the LF driver stage, and
the boost converter. The oscillator requires an external clock source, which can either be an
active signal from a microcontroller for example, or a passive oscillation device like a crystal or a
ceramic resonator. As the LF carrier frequency is directly derived from this clock, the (reso-
nance) frequency of the clock source must be chosen to match the desired LF frequency.
Possible values range from 6.4 MHz to 9.6 MHz, where 8 MHz is the typical value resulting in an
LF frequency of 125 kHz.
Note that during start-up (i.e., as long as no stable oscillation can be detected), the driving cur-
rent for the crystal is increased to shorten the start-up delay. Furthermore, the IC is only
functional if the oscillator is working properly. That means, during start-up after a power-down
phase, no communication and no operation of the IC is possible until the oscillator reaches its
operation point.
If an external clock source such as a microcontroller is to be used, the logic-level clock signal
must be applied at the OSCI pin, and the OSCO pin must be left open. Note that the chip protec-
tion features, need a clock signal present at the OSCI pin; without this, the chip is not fully
protected. Therefore, if the chip is in any mode but in power-down (reset), a clock signal is
needed.
The oscillator block is, like the control logic and the SPI, supplied by the application-provided
logic supply voltage connected to the pin VIF.
The internal power supply stage provides all internally needed BIAS currents and reference volt-
ages. An integrated one-time-programming (OTP) structure is used to adjust internal settings.
This ensures parameter stability over the production process.
The internal supply block performs monitoring functions to reset or shut down the IC in case of
supply shortages or during power-up. A power-management minimizes current consumption
during power-down mode of the IC.
Another part of this block is the internal 5V voltage regulator. It is supplied by the VS pin, i.e., the
battery supply connection. This voltage is used for all internal analog functions and driving pro-
cesses. It is active as long as the IC is not in power-down mode. To increase stability and quality
of this supply line, it is externally available (pin VCC) for connection to a ceramic capacitor for fil-
tering and buffering. Note that no loads must be connected to this pin.
As with the oscillator, this supply voltage must settle in its operation point prior to any operation.
The control logic checks the status of this voltage and inhibits operation until it reaches the
required level. Furthermore, the driver supply voltage present on the VDSx pins is also moni-
tored. If the level falls below V
Status Register) and driver-related commands cannot be processed. Once the voltage level is
valid again, the Op bit is set again, and operability is restored.
VDS,min
, the operability flag of the chip is cleared (bit Op in the
9125A–RKE–04/08