AD8280 Datasheet, PDF (17/24 Pages) Analog Devices – Lithium Ion Battery Safety Monitor

Also, if the resistor (RTOP) used in the top of the thermistor
bridge circuit is less than 10 kΩ, another resistor (RIN) must be
added in series to the input to the VTx pin (see Figure 46). The
two resistors together must be greater than 10 kΩ (RTOP + RIN >
10 kΩ). This configuration is required only if VTH is not the
AD8280 LDO.
V_TH
R_TOP
R_IN
VTx
THERMISTOR
AD8280
Figure 46. Input Configuration for VTx When Not Using the LDO for VTH
The part can work with both negative temperature coefficient
(NTC) and positive temperature coefficient (PTC) thermistors.
For NTC, the NPTC pin should be tied to logic low (VBOTx
pin); for PTC, the NPTC pin should be tied to logic high (LDO
pin). If the part is set to NTC mode, the OT alarm is tripped
when the voltages at VT1 and VT2 drop below the trip point.
If the part is set to PTC mode, the OT alarm is tripped when
the voltages at VT1 and VT2 rise above the trip point.
NUMBER OF CELLS SELECTION
The part can be configured to work with three, four, five, or six
cells. Table 5 describes how to program the SEL0 and SEL1 pins
to determine the number of cells being monitored. A logic low
represents VBOTx, and a logic high represents the LDO output
voltage. Figure 47 through Figure 49 show how to connect the
cells to the part in a five-cell, four-cell, or three-cell application.
Table 5. SELx Pin Programming
Number of Cells Used
6 cells
5 cells (VIN5 shorted)
4 cells (VIN4 and VIN5 shorted)
3 cells (VIN3, VIN4, and VIN5 shorted)
SEL0
0
0
1
1
SEL1
0
1
0
1
VIN6
+
VIN5
+
VIN4
+
VIN3
+
VIN2
+
VIN1
VIN0
AD8280
Figure 47. Five-Cell Connections for the AD8280
AD8280
VIN6
+
VIN5
+
VIN4
+
VIN3
+
VIN2
VIN1
VIN0
AD8280
Figure 48. Four-Cell Connections for the AD8280
VIN6
VIN5
VIN4
+
VIN3
+
VIN2
+
VIN1
VIN0
AD8280
Figure 49. Three-Cell Connections for the AD8280
THRESHOLD INPUTS
The thresholds (or trip points) are set externally with a voltage
divider providing maximum flexibility. The desired trip point
voltage is connected to the following pins: OV (overvoltage trip
point), UV (undervoltage trip point), and OT (overtemperature
trip point). The +5 V output of either the reference (REF) or the
LDO can be used as the top voltage of the divider. However,
because the reference output is more accurate than the LDO out-
put, the reference output is better suited to power the trip point
setting dividers. If the thermistor dividers used for temperature
sensing are driven from the LDO output, it is recommended that
the LDO be used to drive the OT trip point divider as well for
better temperature drift performance.
Decoupling capacitors (0.1 μF) should be used with the bottom
leg of each divider in addition to a 2.2 μF capacitor at the REF
output, as shown in Figure 45.
The REF pin should be loaded with no more than 25 kΩ of
resistance. Therefore, when using REF to drive three voltage
dividers (OV, UV, and OT), it is recommended that the resis-
tance of each divider total at least 75 kΩ. If driving only two
dividers (OV and UV) with the reference, each divider should
total no less than 50 kΩ.
Rev. C | Page 17 of 24