Datasheet

C
C
O
L
ESR R= 1+
m
2
32KX
OC0 OC1OC1
032-067
TPS65950
www.ti.com SWCS032E–OCTOBER 2008–REVISED JANUARY 2011
Table 12-4. Crystal Electrical Characteristics (continued)
Parameter Min Typ Max Unit
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 + Cpin) pF
Pin-to-pin capacitance 1.6 1.8 pF
Crystal ESR
(2)
75 kΩ
Crystal shunt capacitance, C
O
1 pF
Crystal tolerance at room temperature, 25°C –30 30 ppm
Crystal tolerance versus temperature range (–40°C to 85°C) –200 200 ppm
Maximum drive power 1 μW
Operating drive level 0.5 μW
(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.
(2) The crystal motional resistance Rm relates to the equivalent series resistance (ESR) by the following formula:
Measured with the load capacitance specified by the crystal manufacturer. If CXIN = CXOUT = 10 pF, then C
L
= 5 pF. Parasitic
capacitance from the package and board must also be considered.
When selecting a crystal, the system design must consider the temperature and aging characteristics of a
crystal versus the user environment and expected lifetime of the system.
Table 12-5 and Table 12-6 list the switching characteristics of the oscillator and the input requirements of
the 32.768-kHz input clock, respectively. Figure 12-6 shows the crystal oscillator output in normal mode.
Table 12-5. Base Oscillator Switching Characteristics
Name Parameter Description Min Typ Max Unit
f
P
Oscillation frequency 32.768 kHz
t
SX
Startup time 0.5 s
LOJIT <1:0> = 00 1.8
I
DDA
Active current consumption μA
LOJIT <1:0> = 11 8
Low battery mode (1.2 V) 1
I
DDQ
Current consumption μA
Startup 8
Table 12-6. 32-kHz Crystal Input Clock Timing Requirements
Name Parameter Description Min Typ Max Unit
OC0 1/t
C(32KHZ)
Frequency, 32 kHz 32.768 kHz
OC1 t
W(32KHZ)
Pulse duration, 32 kHz low or high 0.40*t
C(32KHZ)
0.60*t
C(32KHZ)
μs
Figure 12-6. 32-kHz Crystal Input
Copyright © 2008–2011, Texas Instruments Incorporated Clock Specifications 137
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