X3100 Datasheet, PDF (18/40 Pages) Xicor Inc. – 3 or 4 Cell Li-Ion Battery Protection and Monitor IC

X3100/X3101 – Preliminary Information
Over-Current Protection
In addition to monitoring the battery cell voltages, the
X3100 and X3101 continually monitor the voltage VCS₂₁
(VCS₂–VCS₁) across the current sense resistor
(R_SENSE). If VCS₂₁ > V_OC for a time exceeding T_OC,
then the device enters over-current protection mode
(Figure 7). In this mode, the X3100 and X3101
automatically switch the discharge FET OFF (UVP/
OCP=Vcc) and hence prevent current from flowing
through the terminals P+ and P-.
Figure 7. Over-Current Protection
Q2
I_LMON
D1
OVP/LMON
X3100/X3101
V_RGO
Q10
FET Control
Circuitry
P+
Load
VSS
VCS1 VCS2
P-
R_SENSE
The 5VDC voltage regulator output (V_RGO) is always
active during an over-current protection mode.
Once the device enters over-current protection mode,
the X3100 and X3101 begin a load monitor state. In the
load monitor state, a small current (I_LMON=7.5µA typ.) is
passed out of pin OVP/LMON in order to determine the
load resistance. The load resistance is the impedance
seen looking out of pin OVP/LMON, between terminal
P+ and pin VSS (See Figure 7.)
If the load resistance > 150kΩ (I_LMON=0µA) for a time
exceeding T_OCR, then the X3100 or X3101 is released
from over-current protection mode. The discharge FET
is then automatically switched ON (UVP/OCP=Vss) by
the X3100 or X3101, unless the status of UVP/OCP has
been changed in control register (by manipulating bit
UVPC) during the over-current protection mode.
T_OC/T_OCR are varied using a capacitor (C_OC) connected
between pin OCT and VSS. A list of typical delay times
is shown in Table 23. Note that the value C_OC should be
larger than 1nF.
The delay T_OC and T_OCR that results from a particular
capacitance C_OC can be approximated by the following
equations:
T_OC (ms) ≈ 10,000 x C_OC (µF)
T_OCR (ms) ≈ 10,000 x C_OC (µF)
Table 23. Typical Over-Current Delay Times
Symbol Description
T_OC
Over-current
detection delay
C_OC
0.001µF
Delay
10ms (Typ)
T_OCR
Over-current
release time
0.001µF 10ms (Typ)
The value of V_OC can be selected from the values
shown in Table 6, by setting bits VOC1, VOC0 in the
configuration register using the WCFIG command.
Note: If the Charge FET is turned off, due to an
overcharge condition or by direct command from the
microcontroller, the cells are not in an undervoltage
condition and the pack has a load, then excessive
current may flow through Q10 and diode D1. To
eliminate this effect, the gate of Q10 can be turned off by
the microcontroller through an unused X3101 cell
balance output, or directly from a microcontroller port
instead of connecting to V_RGO.
REV 1.1.8 12/10/02
www.xicor.com
Characteristics subject to change without notice. 18 of 40