Rainbow Electronics ATA6834 - Manual (Page 7)

7
9122B–AUTO–10/08
ATA6833/ATA6834 [Preliminary]
3.3 5V/3.3V VCC Regulator
The 5V/3.3V regulator is fully integrated. It requires an external electrolytic capacitor in the range
of 2.2 µF up to 10 µF and with an ESR in the range from 2
Ω
to 15
Ω
for stability (see Figure 3-2 ).
The output voltage can be configured as either 5V or 3.3V by connecting pin VMODE to either
pin VINT or GND. Since the regulator is not designed to be switched between both output volt-
ages during operation, it is advisable to hard-wire VMODE pin. The logic levels of the
microcontroller interface are adapted to the VCC regulator output voltage. The maximum output
current (I
OS1
) of the regulator is 100 mA. For T
J
> 150°C the I
OS1
of ATA6834 is reduced to
80 mA. The VCC regulator has a built-in short circuit protection. A comparator checks the output
voltage of the VCC regulator and keeps the external microcontroller in reset as long as the volt-
age is below the lower operation minimum (shown in
Figure 3-3 3).
Figure 3-2. ESR versus Load Current for External Capacitors with Different Values
Figure 3-3. /RESET as Function of the VCC Output Voltage
0
5
10
15
2 0
2 5
3 0
3 5
4 0
0 2 5 50 75 10 0 12 5 150
Load Current (mA)
ESR (
Ω
)
ESR versus Load Current at Pin VCC
ESR
min
(C
VCC
= 2.2 µF)
ESR
max
(C
VCC
= 2.2 µF)
0
5
10
15
2 0
2 5
0 2 5 50 75 10 0 12 5 150
ESR (
Ω
)
Load Current (mA)
ESR versus Load Current at Pin VCC
ESR
max
(C
VCC
= 10 µF)
ESR
min
(C
VCC
= 10 µF)
100% VCC
0V
VCC
/RESET
80% VCC
88% VCC