ISL78610 Datasheet, PDF (22/98 Pages) Intersil Corporation – Multi-Cell Li-Ion Battery Manager

ISL78610
Device Description and
Operation
The ISL78610 is a Li-ion battery manager IC that supervises up
to 12 series connected cells. Up to 14 ISL78610 devices can be
connected in series to support systems with up to 168 cells. The
ISL78610 provides accurate monitoring, cell balance control and
diagnostic functions. The ISL78610 includes a voltage reference,
14-bit A/D converter and registers for control and data.
When multiple ISL78610 devices are connected to a series of
cells, their power supply domains are normally non-overlapping.
The lower (VSS) supply of each ISL78610 nominally connects to
the same potential as the upper (V_BAT) supply of the ISL78610
device below.
Within each device, the cell voltage monitoring system
comprises two basic elements; a level shift to eliminate the cell
common-mode voltage and an analog-to-digital conversion of the
cell voltage.
Each ISL78610 is calibrated at a specific cell input voltage value,
V_NOM. Cell voltage measurement error data is given in
“MEASUREMENT SPECIFICATIONS” on page 8 for various voltage
and temperature ranges with voltage ranges defined with
respect to V_NOM. Plots showing the typical error distribution over
the full input range are included in the “Performance Curves”
section beginning on page 16.
To collect cell voltage and temperature measurements, the
ISL78610 provides two multiple parameter measurement
“scanning” modes in addition to single parameter direct
measurement capability. The scanning modes provide pseudo
simultaneous measurement of all cell voltages in the stack.
The ISL78610 does not measure current. The system performs
this separately using other measurement systems.
The only filtering applied to the ADC measurements is that
resulting from external protection circuits and the limited
bandwidth of the measurement path. No additional filtering is
performed within the part. This arrangement is typically needed
to maintain timing integrity between the cell voltage and pack
current measurements. However, the ISL78610 does apply
filtering to the fault detection systems.
Cell balancing is an important function in a battery pack
consisting of a stack of multiple Li-ion cells. As the cells charge
and discharge, differences in each cell’s ability to take on, and
give up charge, typically leads to cells with different states of
charge. The problem with a stack of cells having different states
of charge is that Li-ion cells have a maximum voltage, above
which it should not be charged, and a minimum voltage, below
which it should not be discharged. The extreme case, where one
cell in the stack is at the maximum voltage and one cell is at the
minimum voltage, results in a nonfunctional battery stack, since
the battery stack cannot be charged or discharged.
The ISL78610 provides multiple cell balance modes, Manual
Balance mode, Timed Balance mode, and Auto Balance mode.
These are described in more detail in “Alarm Response” on
page 75.
The ISL78610 incorporates extensive fault diagnostics functions
which include cell overvoltage and undervoltage, regulator and
oscillator operation, open cell input detection and
communication faults. The current status of most faults is
accessible using the ISL78610 registers. Some communication
faults are reported by special responses to system commands
and some as “unprompted” responses from the device detecting
the fault to the host microcontroller through the daisy chain.
To conserve power, the ISL78610 has three main power modes:
Normal mode, Sleep mode and “off” (Shutdown mode).
Sleep mode is entered in response to a Sleep command or after
a watchdog timeout (see “Watchdog Function” on page 75.) Only
the communications input circuits, low speed oscillator and
internal registers are active in Sleep mode, allowing the part to
perform timed scan and balancing activity and to wake up in
response to communications.
With the Enable pin low the device is in Shutdown mode. In this
mode, the internal bias for most of the IC is powered down
except digital core, Sleep mode regulators and digital input
buffers. When exiting, the device powers up and does not reload
the factory programmed configuration data from EEPROM.
The Normal mode consists of an Active state and a Standby
state. In the Standby state, all systems are powered and the
device is ready and waiting to perform an operation in response
to commands from the host microcontroller. In the Active state,
the device is performing an operation, such as ADC conversion,
open-wire detection, etc.
System Hardware Connection
Battery and Cell Balance Connection
The first consideration in designing a battery system around the
ISL78610 is the connection of the cells to the IC.
The battery connection elements are split between the cell
monitor connections (VCn) and the cell balance connections
(CBn).
BATTERY CONNECTION
All inputs to the ISL78610 VCn pins are protected against battery
voltage transients by external RC filters. The basic input filter
structure, with capacitors to the local ground, provides protection
against transients and EMI for the cell inputs. They carry the loop
currents produced by EMI and should be placed as close to the
battery connector as possible. The ground terminals of the
capacitors must be connected directly to a solid ground plane. Do
not use vias to connect these capacitors to the input signal path
or to ground. Any vias should be placed in line to the signal inputs
so that the inductance of these forms a low pass filter with the
grounded capacitors.
The resistors on the input filter provide a current limit function
during hot plug events. The ISL78610 is calibrated for use with 1kΩ
series protection resistors at the VCn inputs. The VBAT connection
uses a lower value input resistor to accommodate the supply current
of the ISL78610. As much as possible, the time constant produced
by the filtering applied to VBAT should be matched to that applied to
the VCn monitoring inputs. See Figure 38.
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FN8830.1
June 16, 2016