Rainbow Electronics ATA6823 - Manual (Page 9)

9
4856E–AUTO–07/07
ATA6823 [Preliminary]
5.4 5V/3.3V VCC Regulator
The 5V/3.3V regulator is fully integrated on-chip. It requires only a 2.2 µF ceramic capacitor for
stability and has 100 mA current capability. Using the VMODE pin, the output voltage can be
selected to either 5V or 3.3V. Switching of the output voltage during operation is not intended to
be supported. The VMODE pin must be hard-wired to either VINT for 5V or to GND for 3.3V. The
logic HIGH level of the microcontroller interface will be adapted to the VCC regulator voltage.
The output voltage accuracy is in general < ±3%; in the 5V mode with V
VBAT
< 8V it is limited to
< 5%.
To prevent destruction of the IC, the current delivered by the regulator is limited to maximum
160 mA to 320 mA. The delivered voltage will break down and a reset may occur.
Please note that this regulator is the main heat source on the chip. The maximum output current
at maximum battery voltage and high ambient temperature can only guaranteed if the IC is
mounted on an efficient heat sink.
A power-good comparator checks the output voltage of the VCC regulator and keeps the exter-
nal microcontroller in reset as long as the voltage is too low.
5.5 Reset and Watchdog Management
The timing basis of the watchdog is provided by the trimmed internal oscillator. Its period T
OSC
is
adjustable via the external resistor R
WD
.
The watchdog expects a triggering signal (a rising edge) from the microcontroller at the WD
input within a period time window of T
WD
. In order to save current consumption, the watchdog is
switched off during Sleep mode.
Figure 5-2. Timing Diagram of the Watchdog Function
5.5.1 Timing Sequence
For example, with an external resistor R
WD
= 33 k
Ω
±1% we get the following typical parameters
of the watchdog.
T
OSC
= 12.32 µs, t
1
= 12.1 ms, t
2
= 9.61 ms, T
WD
= 16.88 ms ±10%
The times t
res
= 68 ms and t
d
= 68 ms are fixed values with a tolerance of 10%.
t
2
t
1
t
2
t
1
t
d
t
d
t
resshort t
res
WD
/RESET