MHz External Crystal Oscillator (ECO) on CY8CKIT-050 and CY8CKIT-010 – KBA210673

Version: **

 

Question:

How do I configure PSoC® 5LP kit hardware and firmware to use the MHz External Crystal Oscillator (ECO)?

 

Answer:

See the following table that lists the internal main oscillator (IMO) accuracy of PSoC 3 and PSoC 5LP devices:

                                                                                                      

DevicesPSoC 3PSoC 5LP
CY8C32 familyCY8C34 familyCY8C36 familyCY8C38 familyCY8C52LP familyCY8C54LP familyCY8C56LP familyCY8C58LP family
Accuracy at 3 MHz±2%±2%±1%±1%±2%±2%±1%±1%

 

See the “IMO AC Specifications” section in the respective device family’s datasheet for data on accuracy of IMO at different frequencies.

 

If the maximum PPM error of the IMO exceeds the maximum allowed PPM error of the Component that you use in your design, you must use an ECO. Watch this video to know on when to choose ECO, based on the PPM error of different crystal oscillators and the maximum allowed PPM error of some Components such as USB and CAN.

 

Hardware Configuration 

 

The MHz crystal must be placed between the XTAL pins of the PSoC device. The Load Capacitor value will be specified in the crystal datasheet. The capacitors have to be mounted appropriately as shown in Figure 1.

 

The Load Capacitor network along with the crystal gives a phase shift of 180 degrees. Another 180-degree phase shift is given by the inbuilt inverter to make the total phase shift as 360 degrees; this causes self-sustained oscillations of specified frequency to be generated. This arrangement is shown in Figure 1.

 

Figure 1: Oscillator Topology

 

1.png

 

If the load capacitors are not properly chosen to meet the specification of the given crystal, there will be a shift in the operating frequency.  This can be caused due to parasitic pin capacitance. This effect is called Trim Sensitivity. To know more on how to choose the accurate capacitor values, refer to AN54439.

 

The MHz ECO pin can create noise in neighboring pins or vice versa. This electrical interference can be reduced from proper pin assignment. Noisy, high-frequency, and sensitive signals are assigned away from MHz crystal pins. The best practice is to place ground next to XTAL pins.

 

Component designators and part numbers are shown for each kit in the tables below:

 

CY8CKIT-050 MHz ECO Components:

                                                                      

DesignatorComponent DescriptionManufacturerManufacturer Part Number
Y3CRYSTAL 24.000MHZ 20PF SMDECS IncECS-240-20-5PX-TR
C30,C31CAP, CER, 22 pF, 50V, 5%, COG, 0603, SMDPanasonic - ECG       ECJ-0EC1H220J

 

CY8CKIT-010 MHz ECO Components:

                                                                      

DesignatorComponent DescriptionManufacturerManufacturer Part Number
Y2CRYSTAL, 24 MHz, 30 ppm, HC49, SMDECS IncECS-240-12-5PX-TR
C26,C27CAP, CER, 12 pF, 50V, 5%, COG, 0603, SMDMurata Electronics North AmericaGRM1885C1H120JA01D

 

in the respective device family’s datasheet for data on accuracy of IMO at different frequencies.

 

Firmware Configuration

 

The MHz ECO can be configured using the Design Wide Resources interface in PSoC Creator. To enable the MHz ECO, make sure the “XTAL” checkbox in the upper left corner of the “Configure System Clocks” dialog is checked, as shown in Figure 2. For understanding APIs to control clock settings in firmware, refer to PSoC Creator > Help > Reference > System Reference Guide > Clocking.

 

Figure 2: Clock Tree

 

2.png

 

The Configuration window of XTAL is shown in Figure 3.

 

Figure 3: Configuration Window of XTAL

 

3.png

 

The automatic gain control (AGC) option allows the MHz ECO to increase or reduce the inverter gain to increase or reduce the oscillation amplitude. This can increase or decrease the drive level. If fault recovery is enabled, the device automatically switches to the IMO clock when the ECO fails.