TC1796 Datasheet, PDF (78/134 Pages) Infineon Technologies AG – 32-Bit Single-Chip Microcontroller TriCore

TC1796
Functional Description
optimized together with the crystal vendor using the negative resistance method.
Oscillation measurement with the final target system is strongly recommended to verify
the input amplitude at XTAL1 and to determine the actual oscillation allowance (margin
negative resistance) for the oscillator-crystal system.
When using an external clock signal, it must be connected to XTAL1. XTAL2 is left open
(unconnected). The external clock frequency can be in the range of 0 - 40 MHz if the PLL
is bypassed and 4 - 40 MHz if the PLL is used.
The oscillator can also be used in combination with a ceramic resonator. The final
circuitry must be also verified by the resonator vendor.
Figure 20 shows the recommended external oscillator circuitries for both operating
modes, external crystal mode and external input clock mode.
V_DDOSC V_DDOSC3
V_DDOSC V_DDOSC3
XTAL1
f_OSC
4 - 25
MHz
TC1796
R_Q
R_X2
Oscillator
XTAL2
C_X1
C_X2
External Clock
Signal 4¹⁾ - 40
XTAL1
f_OSC
MHz
TC1796
Oscillator
XTAL2
Fundamental
Mode Crystal
V_SSOSC
Crystal Frequency C_X1, C_X2 ¹⁾
4 MHz
33 pF
8 MHz
18 pF
12 MHz
12 pF
16 - 25 MHz
10 pF
R_X2 ¹⁾
0
0
0
0
1) Note that these are evaluation start values!
V_SSOSC
1) in case of PLL bypass 0 MHz
MCS05601
Figure 20 Oscillator Circuitries
A block capacitor between V_DDOSC1)/V_DDOSC3 and V_SSOSC is recommended, too.
Note: For crystal operation, it is strongly recommended to measure the negative
resistance in the final target system (layout) to determine the optimum parameters
1) V_DDOSC and V_SSOSC are not bonded externally in the BC and BD steps of TC1796. An option for bonding them
in future steps and products is kept open.
Data Sheet
78
V1.0, 2008-04