User Manual
90
Rev. 1.1
2019-03-18
TLE984xQX
Microcontroller with LIN and Power Switches for Automotive Applications
System Control Unit - Digital Modules (SCU-DM)
7.3.2
High Precision Oscillator Circuit (OSC_HP)
The high precision oscillator circuit, designed to work with both an external crystal oscillator or an external
stable clock source, consists of an inverting amplifier with XTAL1 as input, and XTAL2 as output.
shows the recommended external circuitries for both operating modes, External Crystal Mode and
External Input Clock Mode.
7.3.2.1
External Input Clock Mode
When supplying the clock signal directly, not using an external crystal and bypassing the oscillator, the input
frequency needs to be within the range of 4 MHz to 24 MHz if the PLL VCO part is used.
When using an external clock signal it must be connected to XTAL1. XTAL2 is left open (unconnected).
7.3.2.2
External Crystal Mode
When using an external crystal, its frequency can be within the range of 4 MHz to 6 MHz. An external oscillator
load circuitry must be used, connected to both pins, XTAL1 and XTAL2. It consists normally of the two load
capacitances C1 and C2, for some crystals a series damping resistor might be necessary. The exact values and
related operating range are dependent on the crystal and have to be determined and optimized together with
the crystal vendor using the negative resistance method. As starting point for the evaluation, the following
load cap values may be used:
Figure 27 TLE984xQX External Circuitry for the OSC_HP
Table 31 External
CAP
Capacitors
Fundamental Mode Crystal Frequency (approx., MHz) Load Caps
C
1
,
C
2
(pF)
4
33
5
22
6
18
ext_osc
OSC_HP
C
1
4 - 6
MHz
C
2
XTAL1
XTAL2
OSC_HP
XTAL1
XTAL2
External Clock
Signal
Fundamental
Mode Crystal
External Crystal Mode
External Input Clock Mode
V
DDP
f
OSC
f
OSC
V
SS
V
SS
V
DDP
V
SS
= GND