X3102 Datasheet, PDF (25/32 Pages) Intersil Corporation – 3 Cell Li-Ion Battery Protection and Monitor IC

X3102
Monitor Mode
Analog Multiplexer Selection
The X3102 can be used to externally monitor individual
battery cell voltages, and battery current. Each quantity can
be monitored at the analog output pin (AO), and is selected
using the analog select (AS0–AS2) pins (Table 25). Also,
see Figure 15.
TABLE 25. AO SELECTION MAP
AS2 AS1 AS0
AO OUTPUT
L
L
L V_SS(1)
L
L
H VCELL₁–VCELL₂ (VCELL₁₂)
L
H
L VCELL₂–VCELL₃ (VCELL₂₃)
L
H
H VCELL₃–VCELL₄ (VCELL₃₄)
H
L
L VCELL₄–Vss (VCELL₄)
H
L
H VCS₁–VCS₂ (VCS₁₂)⁽²⁾
H
H
L VCS2–VCS₁ (VCS₂₁)⁽²⁾
H
H
H V_SS
NOTES:
1. This is the normal state of the X3102. While in this state Over-
charge and Over-discharge Protection conditions are
periodically monitored (See “Periodic Protection Monitoring” on
page 19.)
2. VCS₁, VCS₂ are read at AO with respect to a DC bias voltage of
2.5V (See section “Current Monitor Function” on page 25).
Current Monitor Function
The voltages monitored at pins VCS₁ and VCS₂ can be
used to calculate current flowing through the battery
terminals, using an off-board microcontroller with an A/D.
Since the value of the sense resistor (R_SENSE) is small
(typically in the order of tens of mΩ), and since the resolution
of various A/D converters may vary, the voltage across
R_SENSE (VCS₁ and VCS₂) is amplified internally with a gain
of between 10 and 160, and output to pin AO (Figure 15).
Voltage
Level
Shifters
Cell 1 Voltage
Cell 2 Voltage
Cell 3 Voltage
Cell 4 Voltage
2.5V
R2
OP1
+
-
R1
R2
R1
Config
Gain
SPI
Register _Setting
I/F
CSG1 CSG0
Cross-Bar
Switch
Overcurrent
Protection
AS0
AS1
AS2
AO
S0
SCL
CS
SI
VCS₁
VCS₂
R_SENSE
FIGURE 15. MONITOR CIRCUIT
X3102
P-
The internal gain of the X3102 current sense voltage
amplifier can be selected by using the WCNTR Instruction to
set bits CSG1 and CSG0 in the control register (Table 14).
The CSG1 and CSG0 bits select one of four input resistors
to Op Amp OP1. The feedback resistors remain constant.
This ratio of input to feedback resistors determines the gain.
Putting external resistors in series with the inputs reduces the
gain of the amplifier.
VCS1 and VCS2 are read at AO with respect to a DC bias
voltage of 2.5V. Therefore, the voltage range of VCS₁₂ and
VCS₂₁ changes depending upon the direction of current flow
(i.e. battery cells are in Charge or Discharge - Table 21).
TABLE 26. AO VOLTAGE RANGE FOR VCS₁₂ AND VCS₂₁
AO
VCS₁₂
VCS₁₂
VCS₂₁
VCS₂₁
CELL STATE
Charge
Discharge
Charge
Discharge
AO VOLTAGE RANGE
2.5V ≤ AO ≤ 5.0V
0V ≤ AO ≤ 2.5V
0V ≤ AO ≤ 2.5V
2.5V ≤ AO ≤ 5.0V
By calculating the difference of VCS₁₂ and VCS₂₁ the offset
voltage of the internal op-amp circuitry is cancelled. This
allows for the accurate calculation of current flow into and
out of the battery cells.
Pack current is calculated using the following formula:
Pack Current = -----------------------------⁽--^V-----^C-----^S----¹---²----–-----^V----^C-----^S----²---¹---⁾-----------------------------
(2)(gain setting)(current sense resistor)
25
FN8246.0
December 22, 2004