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)
037-042
TPS65930/TPS65920
www.ti.com SWCS037G–MAY 2008–REVISED APRIL 2011
11.2.3.1 External Crystal Description
Figure 11-5 shows the 32-kHz oscillator block diagram 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 11-5. 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 14-1.
Table 11-4 lists the required electrical constraints.
Table 11-4. 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
Internal capacitor on each input (Cint) 10 pF
Parallel input capacitance (Cpin) 1 pF
Nominal load cap on each oscillator input CXIN and CXOUT
(1)
CXIN = CXOUT = Cosc*2 – (Cint + pF
Cpin)
Pin-to-pin capacitance 1.6 1.8 pF
(1) Nominal load capacitor on each oscillator input defined as CXIN = CXOUT = Cosc*2 – (Cint + Cpin). Cosc is the load capacitor defined
in the crystal oscillator specification, Cint is the internal capacitor, and Cpin is the parallel input capacitor.
Copyright © 2008–2011, Texas Instruments Incorporated Clock Specifications 87
Submit Documentation Feedback
focus.ti.com: TPS65930/TPS65920