Datasheet

MSP430FR4133, MSP430FR4132, MSP430FR4131
SLAS865B –OCTOBER 2014–REVISED AUGUST 2015 www.ti.com
5.12.3 Clock Specifications
Table 5-3. XT1 Crystal Oscillator (Low Frequency)
over recommended ranges of supply voltage and operating free-air temperature (unless otherwise noted)
(1)
PARAMETER TEST CONDITIONS V
CC
MIN TYP MAX UNIT
XT1 oscillator crystal, low
f
XT1, LF
LFXTBYPASS = 0 32768 Hz
frequency
Measured at MCLK,
DC
XT1, LF
XT1 oscillator LF duty cycle 30% 70%
f
LFXT
= 32768 Hz
XT1 oscillator logic-level square-
f
XT1,SW
LFXTBYPASS = 1
(2)(3)
32768 Hz
wave input frequency
LFXT oscillator logic-level square-
DC
XT1, SW
LFXTBYPASS = 1 40% 60%
wave input duty cycle
Oscillation allowance for LFXTBYPASS = 0, LFXTDRIVE = {3},
OA
LFXT
200 kΩ
LF crystals
(4)
f
LFXT
= 32768 Hz, C
L,eff
= 12.5 pF
Integrated effective load
C
L,eff
See
(6)
1 pF
capacitance
(5)
f
OSC
= 32768 Hz,
t
START,LFXT
Start-up time
(7)
LFXTBYPASS = 0, LFXTDRIVE = {3}, 1000 ms
T
A
= 25°C, C
L,eff
= 12.5 pF
f
Fault,LFXT
Oscillator fault frequency
(8)
XTS = 0
(9)
0 3500 Hz
(1) To improve EMI on the LFXT oscillator, the following guidelines should be observed.
• Keep the trace between the device and the crystal as short as possible.
• Design a good ground plane around the oscillator pins.
• Prevent crosstalk from other clock or data lines into oscillator pins XIN and XOUT.
• Avoid running PCB traces underneath or adjacent to the XIN and XOUT pins.
• Use assembly materials and processes that avoid any parasitic load on the oscillator XIN and XOUT pins.
• If conformal coating is used, make sure that it does not induce capacitive or resistive leakage between the oscillator pins.
(2) When LFXTBYPASS is set, LFXT circuits are automatically powered down. Input signal is a digital square wave with parametrics
defined in the Schmitt-trigger inputs section of this data sheet. Duty cycle requirements are defined by DC
LFXT, SW
.
(3) Maximum frequency of operation of the entire device cannot be exceeded.
(4) Oscillation allowance is based on a safety factor of 5 for recommended crystals. The oscillation allowance is a function of the
LFXTDRIVE settings and the effective load. In general, comparable oscillator allowance can be achieved based on the following
guidelines, but should be evaluated based on the actual crystal selected for the application:
• For LFXTDRIVE = {0}, C
L,eff
= 3.7 pF.
• For LFXTDRIVE = {1}, 6 pF ≤ C
L,eff
≤ 9 pF.
• For LFXTDRIVE = {2}, 6 pF ≤ C
L,eff
≤ 10 pF.
• For LFXTDRIVE = {3}, 6 pF ≤ C
L,eff
≤ 12 pF.
(5) Includes parasitic bond and package capacitance (approximately 2 pF per pin).
(6) Requires external capacitors at both terminals. Values are specified by crystal manufacturers.
(7) Includes startup counter of 1024 clock cycles.
(8) Frequencies above the MAX specification do not set the fault flag. Frequencies in between the MIN and MAX specification may set the
flag. A static condition or stuck at fault condition sets the flag.
(9) Measured with logic-level input frequency but also applies to operation with crystals.
22 Specifications Copyright © 2014–2015, Texas Instruments Incorporated
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