X3100 Datasheet, PDF (5/40 Pages) Xicor Inc. – 3 or 4 Cell Li-Ion Battery Protection and Monitor IC

X3100, X3101
PRINCIPLES OF OPERATION
The X3100 and X3101 provide two distinct levels of
functionality and battery cell protection:
First, in Normal mode, the device periodically checks
each cell for an over-charge and over-discharge state,
while continuously watching for a pack over-current
condition. A protection mode violation results from an
over-charge, over-discharge, or over-current state.
The thresholds for these states are selected by the
user through software. When one of these conditions
occur, a Discharge FET or a Charge FET or both FETs
are turned off to protect the battery pack. In an over-
discharge condition, the X3100 and X3101 devices go
into a low power sleep mode to conserve battery
power. During sleep, the voltage regulator turns off,
removing power from the microcontroller to further
reduce pack current.
Second, in Monitor mode, a microcontroller with A/D
converter measures battery cell voltage and pack cur-
rent via pin AO and the X3100 or X3101 on-board MUX.
The user can thus implement protection, charge/dis-
charge, cell balancing or gas gauge software algorithms
to suit the specific application and characteristics of the
cells used. While monitoring these voltages, all protec-
tion circuits are on continuously.
In a typical application, the microcontroller is also pro-
grammed to provide an SMBus interface along with
the Smart Battery System interface protocols. These
additions allow an X3100 or X3101 based module to
adhere to the latest industry battery pack standards.
TYPICAL APPLICATION CIRCUIT
The X3100 and X3101 have been designed to operate
correctly when used as connected in the Typical Appli-
cation Circuit (see Figure 1 on page 5).
The power MOSFET’s Q1 and Q2 are referred to as
the “Discharge FET” and “Charge FET,” respectively.
Since these FETs are p-channel devices, they will be
ON when the gates are at V_SS, and OFF when the
gates are at V_CC. As their names imply, the discharge
FET is used to control cell discharge, while the charge
FET is used to control cell charge. Diode D1 allows the
battery cells to receive charge even if the Discharge
FET is OFF, while diode D2 allows the cells to dis-
charge even if the charge FET is OFF. D1 and D2 are
integral to the Power FETs. It should be noted that the
cells can neither charge nor discharge if both the
charge FET and discharge FET are OFF.
Power to the X3100 or X3101 is applied to pin VCC via
diodes D6 and D7. These diodes allow the device to
be powered by the Li-Ion battery cells in normal oper-
ating conditions, and allow the device to be powered
5
by an external source (such as a charger) via pin P+
when the battery cells are being charged. These
diodes should have sufficient current and voltage rat-
ings to handle both cases of battery cell charge and
discharge.
The operation of the voltage regulator is described in
section “Voltage Regulator” on page 22. This regulator
provides a 5VDC±0.5% output. The capacitor (C1)
connected from RGO to ground provides some noise
filtering on the RGO output. The recommended value
is 0.1µF or less. The value chosen must allow V_RGO to
decay to 0.1V in 170ms or less when the X3100 or
X3101 enter the sleep mode. If the decay is slower
than this, a resistor (R1) can be placed in parallel with
the capacitor.
During an initial turn-on period (T_PUR + T_OC), V_RGO
has a stable, regulated output in the range of 5VDC ±
10% (see Figure 2). The selection of the microcontrol-
ler should take this into consideration. At the end of
this turn on period, the X3100 and X3101 “self-tunes”
the output of the voltage regulator to 5V+/-0.5%. As
such, V_RGO can be used as a reference voltage for the
A/D converter in the microcontroller. Repeated power-
up operations, consistently re-apply the same “tuned”
value for V_RGO.
Figure 1 shows a battery pack temperature sensor
implemented as a simple resistive voltage divider, uti-
lizing a thermistor (R_T) and resistor (R_T’). The voltage
V_T can be fed to the A/D input of a microcontroller and
used to measure and monitor the temperature of the
battery cells. R_T’ should be chosen with consideration
of the dynamic resistance range of R_T as well as the
input voltage range of the microcontroller A/D input.
An output of the microcontroller can be used to turn on
the thermistor divider to allow periodic turn-on of the
sensor. This reduces power consumption since the
resistor string is not always drawing current.
Diode D3 is included to facilitate load monitoring in an
Over-current protection mode (see section “Over-Cur-
rent Protection” on page 19), while preventing the flow
of current into pin OVP/LMON during normal opera-
tion. The N-Channel transistor turns off this function
during the sleep mode.
Resistor R_PU is connected across the gate and drain
of the charge FET (Q2). The discharge FET Q1 is
turned off by the X3100 or X3101, and hence the volt-
age at pin OVP/LMON will be (at maximum) equal to
the voltage of the battery terminal, minus one forward
biased diode voltage drop (V_P+ - V_D7). Since the drain
of Q2 is connected to a higher potential (V_P+) a pull-up
resistor (R_PU) in the order of 1MΩ should be used to
ensure that the charge FET is completely turned OFF
when OVP/LMON = V_CC.
FN8110.0
April 11, 2005