AT43USB325E-AU Atmel, AT43USB325E-AU Datasheet - Page 20

• Manufacturer Part Number: AT43USB325E-AU
• Description: IC USB KEYBOARD CTRLR 64LQFP
• Manufacturer: Atmel
• Series: AVR®r

Specifications of AT43USB325E-AU

• Applications: Keyboard Controller
• Core Processor: AVR
• Program Memory Type: SRAM (16 kB)
• Controller Series: AT43USB
• Ram Size: 512 x 8
• Interface: SPI, 3-Wire Serial
• Number Of I /o: 42
• Voltage - Supply: 4.4 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

4. Functional Description
4.1
4.2
4.3
20
On-chip Power Supply
I/O Pin Characteristics
Oscillator and PLL
AT43USB325
The AT43USB325 contains two on-chip power supplies that generate 3.3V with a capacity of 30
mA each from the 5V power input. The on-chip power supplies are intended to supply the
AT43USB325 internal circuit and the 1.5K pull-up resistor only and should not be used for other
purposes. External 2.2 µF filter capacitors are required at the power supply outputs, CEXT1 and
CEXT2. The internal power supplies can be disabled as described in the next paragraph.
The user should be careful when the GPIO pins are required to supply high-load currents. If the
application requires that the GPIO supply currents beyond the capability of the on-chip power
supply, the AT43USB325 should be supplied by an external 3.3V power supply. In this case, the
5V V
through the CEXT1 and CEXT2 pins.
The I/O pins of the AT43USB325 should not be directly connected to voltages less than V
more than the voltage at the CEXT pins. If it is necessary to violate this rule, insert a series resis-
tor between the I/O pin and the source of the external signal source that limits the current into
the I/O pin to less than 2 mA. Under no circumstance should the external voltage exceed 5.5V.
To do so will put the chip under excessive stress.
All clock signals required to operate the AT43USB325 are derived from an on-chip oscillator. To
reduce EMI and power dissipation, the oscillator is designed to operate with a 6 MHz crystal. An
on-chip PLL generates the high frequency for the clock/data separator of the Serial Interface
Engine. In the suspended state, the oscillator circuitry is turned off.
The oscillator of the AT43USB325 is a special, low-drive type, designed to work with most crys-
tals without any external components. The crystal must be of the parallel resonance type
requiring a load capacitance of about 10 pF. If the crystal requires a higher value capacitance,
external capacitors can be added to the two terminals of the crystal and ground to meet the
required value. To assure quick start-up, a crystal with a high Q, or low ESR, should be used. To
meet the USB hub frequency accuracy and stability requirements for hubs, the crystal should
have an accuracy and stability of better than 100 PPM. The use of a ceramic resonator in place
of the crystal is not recommended because a resonator would not have the necessary frequency
accuracy and stability.
The clock can also be externally sourced. In this case, connect the clock source to the XTAL1
pin, while leaving XTAL2 pin floating. The switching level at the OSC1 pin can be as low as
0.47V and a CMOS device is required to drive this pin to maintain good noise margins at the low
switching level.
For proper operation of the PLL, an external RC filter consisting of a series RC network of 100
and 0.1 µF in parallel with a 0.01 µF capacitor must be connected from the LFT pin to V
only high-quality ceramic capacitors.
CC
power supply pin should be left unconnected and the 3.3V power supplied to the chip
3355C–USB–4/05
SS
. Use
SS
or