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| Microcontrollers ApNote AP0825 Power Supply Concept for the C515C 8-Bit Microcontroller This application note introduces a power supply concept for the C515C and deals with the enhanced feature of this controller to switch off the Address Latch Enable (ALE) output signal during accesses to internal ROM. H. Kern / Siemens Application Support Semiconductor Group 05.97, Rel 01 Power Supply Concept for the C515C Contents 1 2 3 4 5 6 Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Dedicated Power Supply Pins of the C515C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 On-chip Power Supply Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 PCB Power Supply Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ALE Switch Off Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 AP0825 ApNote - Revision History Actual Revision : 05.97 Page of Page of actual Rev. prev.Rel. Previous Revision : none (Original Version) Subjects (changes since last release) Semiconductor Group 2 of 6 AP0825 05.97 Power Supply Concept for the C515C 1 Introduction This application note describes a power supply concept for the Siemens C515C 8-Bit microcontroller and introduces a corresponding suggestion for a corresponding PCB schematic. Moreover this paper deals with the enhanced feature of the C515C, which is to switch off the Address Latch Enable output signal (ALE) while accessing internal code memory (ROM). A significant improvement of the EMC behavior of this controller can be achieved with this feature. 2 Dedicated Power Supply Pins of the C515C Ten pins of the C515C 8-Bit microcontroller are dedicated power supply pins, which are more then 12% of all pins of the MQFP 80 package. These pins are arranged and grouped into power supply and ground pins and used to connect the controller to the external 5V power supply. The symbolic names and pin numbers are listed in table 1 and table 2 below. The pin configuration of the C515C is shown in figure 1. 3 On-chip Power Supply Concept The C515C has two on-chip power supply rings. One power ring supplies the core and the peripherals (Oscillator circuit, ADC, Timer Units, SSC, USART, CAN etc.). The other one is used to feed the I/O ports (pads). Each of these two power rings is at least connected to two supply pin pairs. These multiple supply nodes lead to a balanced supply voltage all over the chip and to stable VOL and VOH levels. The pin pairs VCC1/VSS1 and VCCCLK/VSSCLK belong to the power ring for the internal logic. The power ring for the pads is connected to the three supply pin pairs VCCE1/VSSE1, VCCE2/VSSE2 and VCCEXT/VSSEXT. The two power rings are connected internally only at the pins VCC1/VCCE1 and VSS1/VSSE1 over bond wires. Due to this, the interferences between the two power rings are minimized. Additionally, the C515C provides on-chip decoupling capacitors, building in sum approx. 800 pF. These measures lead to an approach towards improved EMC behavior of this device. Table 1 : Supply pin pairs for the core and peripherals Symbol VCC1 VCCCLK Pin Number 33 14 Symbol VSS1 VSSCLK Pin Number 34 13 Function supply pin pair for the core and the peripherals supply pin pair for the on-chip oscillator circuit, the core and the peripherals Table 2 : Supply pin pairs for the I/O ports Symbol VCCE1 VCCE2 VCCEXT Pin Number 32 68 50 Symbol VSSE1 VSSE2 VSSEXT Pin Number 35 70 51 Function supply pin pair for the I/O ports (pads) supply pin pair for the I/O ports (pads) supply pin pair for the I/O ports (pads) Semiconductor Group 3 of 6 AP0825 05.97 Power Supply Concept for the C515C 4 PCB Power Supply Concept In general, separate VCC and VSS planes are recommended for the PCB layout and ceramic SMD capacitors (X7R) should be used as decoupling capacitances in order to obtain best EMC behavior. Figure 1 introduces a suggestion, whereby the controller is connected to the supply voltage with all of its supply pin pairs. The pin pairs VCC1/VSS1 and VCCE1/VSSE1 have also to be connected externally (on the PCB) and can be handled as one supply input (see figure 1). Each supply input should be blocked with a SMD capacitor of 33 nF. These block capacitors should be placed as near as possible to the power supply pins of the controller in order to avoid parasitical inductances. For PCB layouts, which do not use separate VCC and VSS planes, it is recommended to feed the C515C straight from one 5V voltage source to VCC1/VSS1 and to connect the other power supply pins directly to this point. This suggestion may fit for many applications but should not be regarded as the only possible solution. 5V 33nF P5.6 P5.5 P5.4 P5.3 P5.2 P5.1 P5.0 VCCE2 HWPD VSSE2 N.C. P4.0 / ADST P4.1 / SCLK P4.2 / SRI PE / SWD P4.3 / STO P4.4 / SLS P4.5 / INT8 P4.6 / TXDC P4.7 / RXDC RESET N.C. VAREF VAGND P6.7 / AIN7 P6.6 / AIN6 P6.5 / AIN5 P6.4 / AIN4 P6.3 / AIN3 P6.2 / AIN2 P6.1 / AIN1 P6.0 / AIN0 VSSCLK VCCCLK P3.0 / RXD P3.1 / TXD P3.2 / INT0 P3.3 / INT1 P3.4 / T0 P3.5 / T1 80 1 75 70 65 61 60 5 10 33nF C515C P-MQFP-80 Package 55 50 5V 15 45 20 21 25 30 35 41 40 P5.7 P0.7 / AD7 P0.6 / AD6 P0.5 / AD5 P0.4 / AD4 P0.3 / AD3 P0.2 / AD2 P0.1 / AD1 P0.0 / AD0 VSSEXT VCCEXT EA ALE PSEN CPUR P2.7 / A15 P2.6 / A14 P2.5 / A13 P2.4 / A12 P2.3 / A11 33nF 5V Figure 1 : Schematic of the PCB power supply concept for the C515C P2.2 / A10 P2.1 / A9 P2.0 / A8 XTAL1 XTAL2 VSSE1 VSS1 VCC1 VCCE1 P1.0 / INT3 / CC0 P1.1 / INT4 / CC1 P1.2 / INT5 / CC2 P1.3 / INT6 / CC3 P1.4 / INT2 P1.5 / T2EX P1.6 / CLKOUT P1.7 / T2 P7.0 / INT7 P3.7 / RD P3.6 / WR 33nF 5V Semiconductor Group 4 of 6 AP0825 05.97 Power Supply Concept for the C515C 5 ALE Switch Off Feature In order to improve the EMC behavior of this device, when using internal ROM, the C515C allows to switch off the Address Latch Enable output signal (ALE). This enhanced capability can only become active if internal ROM is used (EA=1). With pin EA=1 there is no port activity at Port 0 and Port 2 while accessing internal code memory, but the ALE output signal is still generated. The ALE signal can be suppressed by clearing bit EALE (Enable ALE output) in SFR SYSCON (located at address B1H) and ALE output will only become active during external data memory accesses. After a hardware reset the ALE generation is enabled. Reset value: EALE = 1 The comparison of EMC measurements according to VDE 767.14 indicates the contribution of the ALE output signal to the global EME. The usage of the ALE switch off feature can reduce the global EME up to 15 dBV within the lower frequency range up to 80 MHz during internal code memory accesses. This significant impact of the ALE switch off feature of the C515C is shown in figure 2. The bright curve (C515C ALE ON) corresponds to the measurement done with activated ALE output signal and the dark curve (C515C ALE OFF) corresponds to the measurement done with deactivated ALE output signal while accessing internal ROM (EA=1). Conducted Ground Bouncing Measurement 45 40 35 dBV 30 25 20 15 30,00 MHz 50,00 MHz 70,00 MHz C515C ALE OFF 90,00 MHz 110,00 MHz Frequency 130,00 MHz 150,00 MHz 170,00 MHz 190,00 MHz C515C ALE ON Figure 2 : Comparison of the EME behavior of the C515C with ALE on/off Measurement conditions: EMC measurements according to VDE 767.14 Device: C515C 1 EA: fosc: 8 MHz Supply Voltage: 5 V Temperature: 20 C Note: This VDE EMC measurements are relative measurements covering ground bouncing. EMC investigations done in an absorbing hall with radio meter and antennas may deliver deviating results. Semiconductor Group 5 of 6 AP0825 05.97 Power Supply Concept for the C515C 6 Conclusion Optimized EMC behavior of the application circuit is typically an important demand to be fulfilled in automotive applications. This requirement becomes more and more necessary for other application segments, too. The improved internal power supply concept of the C515C is an approach towards improved EMC behavior of this microcontroller. The explanations and PCB design hints given in this application note show how to use this new internal power supply concept in order to obtain optimized EMC behavior. Additionally, the above described ALE switch off feature of the Siemens C515C 8-Bit microcontroller can contribute to an improved EMC behavior of the application. Semiconductor Group 6 of 6 AP0825 05.97 |
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