Table 15. XOSC External Oscillator electrical specifications
(continued)
Symbol Parameter Conditions
Value Unit
Min Max
f
XTAL
≤ 40 MHz 12 43
V
EXTAL
Oscillation Amplitude on the
EXTAL pin after startup
7
T
J
= –40 °C to 150
°C
0.5 1.6 V
I
XTAL
XTAL current
7
,
8
T
J
= –40 °C to 150
°C
— 14 mA
1. The range is selectable by UTEST miscellaneous DCF clients XOSC_LF_EN and XOSC_EN_40MHZ.
2. This value is determined by the crystal manufacturer and board design.
3. Proper PC board layout procedures must be followed to achieve specifications.
4. Crystal recovery time is the time for the oscillator to settle to the correct frequency after adjustment of the integrated load
capacitor value.
5. This parameter is guaranteed by design rather than 100% tested.
6. See crystal manufacturer's specification for recommended load capacitor (C
L
) values.The external oscillator requires
external load capacitors when operating from 8 MHz to 16 MHz. Account for on-chip stray capacitance (C
S_EXTAL
/C
S_XTAL
)
and PCB capacitance when selecting a load capacitor value. When operating at 20 MHz/40 MHz, the integrated load
capacitor value is selected via S/W to match the crystal manufacturer's specification, while accounting for on-chip and PCB
capacitance. The capacitance on “EXTAL” and “XTAL” by internal capacitance array is controlled by the XOSC LOAD CAP
SEL field of the UTEST Miscellaneous DCF client. See the DCF Records chapter of the Reference Manual.
7. Amplitude on the EXTAL pin after startup is determined by the ALC block, i.e., the Automatic Level Control Circuit. The
function of the ALC is to provide high drive current during oscillator startup, but reduce current after oscillation in order to
reduce power, distortion, and RFI, and to avoid overdriving the crystal. The operating point of the ALC is dependent on the
crystal value and loading conditions.
8. IXTAL is the oscillator bias current out on the XTAL pin with both EXTAL and XTAL pins grounded. This is the maximum
current during startup of the oscillator. The current after oscillation is typically in the 2-3 mA range and is dependant on the
load and series resistance of the crystal. Test circuit is shown in the figure below.
Table 16. Selectable load capacitance
load_cap_sel[4:0] from DCF record Capacitance on EXTAL (C
EXTAL
)/XTAL (C
XTAL
)
, 1, 2
(pF)
00000 1.0
00001 2.0
00010 2.9
00011 3.8
00100 4.8
00101 5.7
00110 6.6
00111 7.5
01000 8.5
01001 9.4
01010 10.3
01011 11.2
01100 12.2
01101 13.1
01110 14.0
Table continues on the next page...
Oscillator and FMPLL
SPC5746R Microcontroller Data Sheet, Rev. 6, 06/2017
24 NXP Semiconductors
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