CC2420ZRTC Datasheet, PDF (53/96 Pages) Texas Instruments – 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver

BATTMON.BATTMON_EN
Internal
bandgap
voltage
reference
1.25 V
VREG_IN
CC2420
BATTMON.BATTMON_OK
BATTMON.BATTMON_VOLTAGE[4:0]
Figure 29. Battery monitor, simplified schematic
The battery monitor is controlled through
the BATTMON control register. The battery
monitor is enabled and disabled using the
BATTMON.BATTMON_EN control bit. The
voltage regulator must also be enabled
when using the battery monitor.
72  BATTMON_VOLTAGE
V  1.25V
toggle
27
Alternatively, for a desired toggle voltage,
BATTMON_VOLTAGE should be set
according to:
The battery monitor status bit is available
in the BATTMON.BATTMON_OK status bit.
This bit is high when the VREG_IN input
voltage is higher than the toggle voltage
V_toggle.
The battery monitor toggle voltage is set in
the 5-bit BATTMON.BATTMON_VOLTAGE
control bits. BATTMON_VOLTAGE is an
unsigned, positive number from 0 to 31.
The toggle voltage is given by:
V _{BATTMON_VOLTAGE  72  27 } toggle
1.25 V
The voltage regulator must be enabled for
at least 100 μs before the first
measurement. After being enabled, the
BATTMON_OK status bit needs 2 μs to
settle for each new toggle voltage
programmed.
The main performance characteristics of
the battery monitor is shown in the
Electrical Specifications section on page 9.
31 Crystal Oscillator
An external clock signal or the internal
crystal oscillator can be used as main
frequency reference. The reference
frequency must be 16 MHz. Because the
crystal frequency is used as reference for
the data rate as well as other internal
signal processing functions, other
frequencies cannot be used.
If an external clock signal is used this
should be connected to XOSC16_Q1, while
XOSC16_Q2 should be left open. The
MAIN.XOSC16M_BYPASS bit must be set
when an external clock signal is used.
Using the internal crystal oscillator, the
crystal must be connected between the
XOSC16_Q1 and XOSC16_Q2 pins. The
oscillator is designed for parallel mode
operation of the crystal. In addition,
loading capacitors (C₃₈₁ and C₃₉₁) for the
crystal are required. The loading capacitor
values depend on the total load
capacitance, C_L, specified for the crystal.
SWRS041c
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