Cypress manual CY8CTST120, CY8CTMG120, CY8CTMA120

CY8CTST120, CY8CTMG120, CY8CTMA120

1.Internal Main Oscillator (IMO) tolerance deviation at temperature extremes.

PROBLEM DEFINITION

Asynchronous digital communication interfaces may fail framing beyond 0 to 70°C. This problem does not affect end product usage between 0 and 70°C.

PARAMETERS AFFECTED

The IMO frequency tolerance. The worst case deviation when operated below 0°C and above +70°C and within the upper and lower data sheet temperature range is ±5%.

TRIGGER CONDITION

The asynchronous Rx/Tx clock source IMO frequency tolerance may deviate beyond the data sheet limit of ±4% when operated beyond the temperature range of 0 to +70°C.

SCOPE OF IMPACT

This problem may affect UART, IrDA, and FSK implementations.

WORKAROUND

Implement a quartz crystal stabilized clock source on at least one end of the asynchronous digital communications interface.

FIX STATUS

The cause of this problem and its solution has been identified. Silicon fix is planned to correct the deficiency in silicon.

2.The DP line of the USB interface may pulse low when the PSoC® device wakes from sleep causing an unexpected wakeup of the host computer

PROBLEM DEFINITION

When the device is operating at 4.75V to 5.25V and the 3.3V regulator is enabled, a short low pulse may be created on the DP signal line during device wakeup. The 15 µs to 20 µs low pulse of the DP line may be interpreted by the host computer as a de-attach or the beginning of a wakeup.

PARAMETERS AFFECTED

The bandgap reference voltage used by the 3.3V regulator decreases during sleep due to leakage. Upon device wakeup, the bandgap is re-enabled and after a delay for settling, the 3.3V regulator is enabled. On some devices the 3.3V regulator that is used to generate the USB DP signal may be enabled before the bandgap is fully stabilized. This can cause a low pulse on the regulator output and DP signal line until the bandgap stabilizes. In applications where Vdd is 3.3V, the regulator is not used; therefore, the DP low pulse is not generated.

WORKAROUND

To prevent the DP signal from pulsing low, keep the bandgap enabled during sleep. The most efficient method is to set the No Buzz bit in the OSC_CR0 register. The No Buzz bit keeps the bandgap powered and output stable during sleep. Setting the No Buzz bit results in a nominal 100 µA increase to sleep current. Leaving the analog reference block enabled during sleep also resolves this issue because it forces the bandgap to remain enabled. An example to disable the No Buzz bit is as follows.

Assembly

M8C_SetBank1

or reg[OSC_CR0], 0x20 M8C_SetBank0

C

OSC_CR0 = 0x20;

September 25, 2008 Document No. 001-49038 Rev. ** 2

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