R
EM3027
9
Power Management
VCC
Switchover
I/O
VHigh
4x Trickle
charger
resistors
VBack
VReg
Logic, EEPROM,
Thermometer,
Voltage Monitor
Xtal
Oscillator
Regulator
2.9V
Figure 6: Power Management
9.1
Power Supplies, Switchover and Trickle Charger
In this way, a rechargeable battery or a super-cap can be
charged from the VCC voltage, as long as VCC > VBack
The device can be supplied from the VCC pin or from the
Back pin.
.
V
There are 4 selectable resistors connected in parallel
with typical values of 80kΩ, 20kΩ, 5kΩ and 1.5kΩ. One
or more resistors can be selected by EEctrl bits setting.
The switchover block implemented inside the chip
compares VCC and VBack voltages and connects the
higher of them to the internal VHigh net that supplies the
chip.
If a Lithium battery shall be connected to VBack pin, a
protection resistor of value up to 1kΩ can be connected
in series with it. In this way, in case of EM3027 device
damage resulting in short between both supply pins,
charging current from the VCC supply can be reduced to
its allowed maximum level as required by UL1642
standard.
Nevertheless, the communication pins (SCL, SDA or CS,
SCK, SI, SO) are supplied from the VCC pin. For that
reason, when serial interface (I2C or SPI) is used, the
chip has to be supplied from VCC. (i.e. VCC > VBack).
By setting of a trickle charger bit in register EEctrl, a
resistor can be inserted between VBack and VHigh voltage.
Clock operating with thermocompensation using either
previously in fully operating mode measured or by user
stored temperature value; no EEPROM write
min max
min max
EM3027 fully operating according datasheet
(clock, thermometer, thermocompensation)
Serial communication
is enabled, if
VCC > VCCmin and
VCC > Vback
Vprog
VCCmin
VCCmax
EEPROM write if VCC > Vprog
5.5V
1.4V
2.2V
Supply Voltage
0V
1.0V
2.0V
3.0V
4.0V
5.0V
Figure 7: EM3027 operating Voltage Areas
Copyright © 2009, EM Microelectronic-Marin SA
12/09 – rev D
www.emmicroelectronic.com
20
EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
