Datasheet

Signalswing
limitingcircuit
Biasgenerator
andstartup
circuit
XI
XO
Signal
shaping
C1 C2
Y
Currentcontrol
circuitand
modeselection
XTAL
Externaltodevice
VBATOK
(1)
Internal
GND
Internal
GND
VBATOK
(1)
032-066
TPS65950
SWCS032E–OCTOBER 2008–REVISED JANUARY 2011 www.ti.com
• An external 32.768-kHz crystal through the 32KXIN/32KXOUT balls (see Figure 12-5). This
configuration is available for master mode only (for more information, see Section 13, Timing
Requirements and Switching Characteristics).
• An external square or sine wave of 32.768 kHz through 32KXIN with amplitude of 1.8 or 1.85 V (see
Figure 12-7, Figure 12-8, and Figure 12-9). This configuration is available for master and slave modes
(for more information, see Section 13, Timing Requirements and Switching Characteristics).
12.2.3.1 External Crystal Description
Figure 12-5 is a block diagram of the 32-kHz oscillator with crystal in master mode.
NOTE: Switches close by default and open only if register access enables very-low-power mode when VBAT < 2.7 V.
Figure 12-5. 32-kHz Oscillator Block Diagram In Master Mode With Crystal
CXIN and CXOUT represent the total capacitance of the printed circuit board (PCB) and components,
excluding the crystal. Their values depend on the datasheet of the crystal, the internal capacitors, and the
parallel capacitor. The frequency of the oscillations depends on the value of the capacitors. The crystal
must be in the fundamental mode of operation and parallel resonant.
NOTE
For the values of CXIN and CXOUT, see Table 15-1.
Table 12-4 lists the required electrical constraints.
Table 12-4. Crystal Electrical Characteristics
Parameter Min Typ Max Unit
Parallel resonance crystal frequency 32.768 kHz
Input voltage, Vin (normal mode) 1.0 1.3 1.55 V
136 Clock Specifications Copyright © 2008–2011, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Link(s): TPS65950