ISL9216IRZ datasheet(24/34 Pages) RENESAS

24 / 34 page

ISL9216, ISL9217

FN6488 Rev 1.00

Page 24 of 34

November 2, 2007

microcontroller can monitor the internal temperature through

the analog output pin (AO), but any writes to the CFET bit,

DFET bit, or cell balancing bits are ignored

The automatic response to an internal over-temperature is

prevented by setting the DISITSD bit to “1”. The automatic

response to an external over-temperature is prevented by

setting the DISXTSD bit to “1”. In either case, it is important for

the microcontroller to monitor the internal and external

temperature to protect the pack and the electronics in an over-

temperature condition.

Analog Multiplexer Selection

The ISL9216 and ISL9217 devices can be used to externally

monitor individual battery cell voltages and temperatures. Each

quantity can be monitored at the analog output pin (AO) and is

selected using the I2C interface. See Figure 6.

To monitor the voltages on the ISL9217 inputs, set the ISL9216

to monitor VCELL6, then set the ISL9217 to the desired

VCELL input. The ISL9216 and ISL9217 VCELL input voltages

are divided by 2, except for the ISL9216 VCELL6 input. This is

a divide by 1 input. In this way, the value read at the ISL9216

AO output is always a divide by 2 of the original cell voltage.

VOLTAGE MONITORING

Since the voltage on each of the Li-Ion Cells are normally

higher than the regulated supply voltage, it is necessary to

both level shift and divide the voltage. To get into the voltage

range required by the external A/D converter, the voltage level

shifter divides the cell voltage by 2. Therefore, a Li-Ion cell with

a voltage of 4.2V is reported via the AO pin to be 2.1V.

TEMPERATURE MONITORING

The voltage representing the external temperature applied at

the TEMPI terminal is directed to the AO terminal through a

MUX, as selected by the AO control bits (see Figures 5 and 6).

The external temperature voltage is not divided by 2 as are the

cell voltages. Instead it is a direct reflection of the voltage at

the TEMPI pin.

A similar operation occurs when monitoring the internal

temperature through the AO output, except there is no external

“calibration” of the voltage associated with the internal

temperature. For the internal temperature monitoring, the

voltage at the output is linear with respect to temperature. (See

“Operating Specifications” on page 6 for information about the

output voltage at +25°C and the output slope relative to

temperature).

Cell Balancing

OVERVIEW

A typical ISL9216 and ISL9217 Li-ion battery pack consists of

8 to 12 cells in series, with one or more cells in parallel. This

combination gives both the voltage and power necessary for

power tools, e-bikes, electric wheel chairs, portable medical

equipment, and battery powered industrial applications. While

the series/parallel combination of Li-ion cells is common, the

configuration is not as efficient as it could be, because any

capacity mismatch between series-connected cells reduces

the overall pack capacity. This mismatch is greater as the

number of series cells and the load current increase. Cell

balancing techniques increase the capacity and the operating

time of Li-ion battery packs.

DEFINITION OF CELL BALANCING

Cell balancing is defined as the application of differential

currents to individual cells (or combinations of cells) in a series

string. Normally, of course, cells in a series string receive

identical currents. A battery pack requires additional

components and circuitry to achieve cell balancing. For the

ISL9216 and ISL9217 devices, the only external components

required are balancing resistors.

VCELL4

VSS

SCL

I2C

FIGURE 6. ANALOG OUTPUT MONITORING DIAGRAM

REGS

AO3:AO0

DECODE

VCELL1

VCELL5

SDA

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

TEMPI

INT

TEMP

MUX

EXT TEMP.

(ISL9216 ONLY)

VCELL2

VSS

I2C

REGS

AO3:AO0

DECODE

VCELL1

VCELL6

VC7/VCC

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

LEVEL

SHIFT

INT

TEMP

MUX

VCELL6

VCC

LEVEL

SHIFT

ISL9216

ISL9217

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