Datasheet

C
C
O
L
ESR R= 1+
m
2
32KX
OC0 OC1OC1
019-019
TPS65930/TPS65920
SWCS037G–MAY 2008– REVISED APRIL 2011 www.ti.com
Table 11-4. Crystal Electrical Characteristics (continued)
Parameter Min Typ Max Unit
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
(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, 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 11-5 and Table 11-6 list the switching characteristics of the oscillator and the timing requirements of
the 32.768-kHz input clock. Figure 11-6 shows the crystal oscillator output in normal mode.
Table 11-5. Base Oscillator Switching Characteristics
Name Parameter Description Min Typ Max Unit
f
P
Oscillation frequency 32.768 kHz
t
SX
Start-up 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 11-6. 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 11-6. 32-kHz Crystal Input
11.2.3.2 External Clock Description
When an external 32K clock is used instead of a crystal, three configuration can be used:
• A square- or sine-wave input can be applied to the 32KXIN pin with amplitude of 1.85 or 1.8 V. The
32KXOUT pin can be driven to a dc value of the square- or sine-wave amplitude divided by 2. This
configuration, shown in Figure 11-7, is recommended if a large load is applied on the 32KXOUT pin.
• A square- or sine-wave input can be applied to the 32KXIN pin with amplitude of 1.85 or 1.8 V. The
32KXOUT pin can be left floating. This configuration, showed in Figure 11-8, is used if no charge is
applied on the 32KXOUT pin.
• The oscillator is in bypass mode and a square-wave input can be applied to the 32KXIN pin with
amplitude of 1.8 V. The 32KXOUT pin can be left floating. This configuration, shown in Figure 11-9, is
88 Clock Specifications Copyright © 2008–2011, Texas Instruments Incorporated
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