X3102 Datasheet, PDF (19/32 Pages) Intersil Corporation – 3 Cell Li-Ion Battery Protection and Monitor IC

X3102
X3102 Internal Protection Functions
The X3102 provides periodic monitoring (See section
“Periodic Protection Monitoring” on page 19) for over-charge
and over-discharge states and continuous monitoring for an
overcurrent state. It has automatic shutdown when a
protection mode is encountered, as well as automatic return
after the device is released from a protection mode. When
sampling voltages through the analog port (Monitor Mode),
over-charge and over-discharge protection monitoring is
also performed on a continuous basis.
Voltage thresholds for each of these protection modes (V_OV,
V_UV, and V_OC respectively) can be individually selected via
software and stored in an internal non-volatile register. This
feature allows the user to avoid the restrictions of mask
programmed voltage thresholds, and is especially useful
during prototype/evaluation design stages or when cells with
slightly different characteristics are used in an existing
design.
Delay times for the detection of, and release from protection
modes (T_OV, T_UV/T_UVR, and T_OC/T_OCR respectively) can be
individually varied by setting the values of external capacitors
connected to pins OVT, UVT, OCT.
Periodic Protection Monitoring
In normal operation, the analog select pins are set such that
AS2 = L, AS1 = L, AS0 = L. In this mode the X3102
conserves power by sampling the cells for over or over-
discharge conditions.
In this state over-charge and over-discharge protection
circuitry are usually off, but are periodically switched on by
the internal Protection Sample Rate Timer (PSRT). The over-
charge and over-discharge protection circuitry is on for
approximately 2ms in each 125ms period. Overcurrent
monitoring is continuous. In monitor mode (See page 25)
over-charge and over-discharge monitoring is also
continuous.
Over-charge Protection
The X3102 monitors the voltage on each battery cell
(V_CELL). If for any cell, V_CELL > V_OV for a time exceeding
T_OV, then the Charge FET will be switched OFF
(OVP/LMON=V_CC). The device has now entered Over-
charge protection mode (Figure 11). The status of the
discharge FET (via pin UVP) will remain unaffected.
While in over-charge protection mode, it is possible to
change the state of the OVPC bit in the control register such
that OVP/LMON=Vss (Charge FET=ON). Although the
OVPC bit in the control register can be changed, the change
will not be seen at pin OVP until the X3102 returns from
over-charge protection mode.
The over-charge detection delay T_OV, is varied using a
capacitor (C_OV) connected between pin OVT and GND. A
typical delay time is shown in Table 10. The delay T_OV that
results from a particular capacitance C_OV, can be
approximated by the following linear equation:
T_OV (s) ≈ 10 x C_OV (µF).
TABLE 19. TYPICAL OVER-CHARGE DETECTION TIME
Symbol
T_OV
C_OV
0.1µF
Delay
1.0s (Typ)
The device further continues to monitor the battery cell
voltages, and is released from over-charge protection mode
when V_CELL< V_OVR, for all cells. When the X3102 is
released from over-charge protection mode, the charge FET
is automatically switched ON (OVP/LMON=V_SS). When the
device returns from over-charge protection mode, the status
of the discharge FET (pin UVP/OCP) remains unaffected.
The value of V_OV can be selected from the values shown in
Table 4 by setting bits VOV1, VOV0. These bits are set by
using the WCFIG instruction to write to the configuration
register.
Normal Operation Mode
Over-charge
Protection Mode
Normal Operation Mode
V_OV
V_CELL
T_OV
OVP/LMON
V_OVR
V_CC
V_SS
Event
0
1
2
3
FIGURE 11. OVER-CHARGE PROTECTION MODE-EVENT DIAGRAM
19
FN8246.0
December 22, 2004