MAX1894XEEE Maxim Integrated, MAX1894XEEE Datasheet - Page 7

• Manufacturer Part Number: MAX1894XEEE
• Description: Battery Management
• Manufacturer: Maxim Integrated
• Series: MAX1894, MAX1924r

The MAX1894/MAX1924 battery-pack protectors super-
vise the charging and discharging process of Li+ cells.
Designed for 3-series (MAX1924V) and 4-series
(MAX1894X/MAX1924X) applications, these devices
monitor the voltage across each cell to provide protec-
tion against undervoltage, overvoltage, and
overcurrent damage.
Output pins CGO, TKO, and DSO control external
MOSFET gates. These MOSFETs, in turn, control the
fast-charging, trickle-charging, and discharge process-
es of the battery pack (Figure 1).
The MAX1894/MAX1924 go into shutdown mode under
two conditions: the SHDN pin is driven high without a
charger applied, or a battery cell undervoltage fault is
detected, also without a charger applied. In shutdown
mode, the device consumes 0.8µA (typ) on the V
and all MOSFETs are off. The MAX1894/MAX1924 stay
in shutdown mode as long as no charging voltage is
applied to the battery pack (V
voltage). When the battery pack is connected to a
charger (V
above 4.5V, the device goes into normal operating
mode and begins monitoring the pack (see Figure 2).
In the normal mode of operation, the MAX1894/MAX1924
are in either a standby mode (29µA typ) or sample mode
(160µA typ). The device enters the standby mode from
shutdown mode. The standby mode lasts for 79ms; then
the device goes into the sample mode. During sample
mode, the MAX1894/MAX1924 check each cell for over-
voltage and undervoltage. Sample mode lasts for 0.5ms;
then the MAX1894/MAX1924 return to standby mode.
During sample mode, the MAX1894/MAX1924 do not intro-
duce cell mismatch.
During normal mode operation, the MAX1894/MAX1924
continuously monitor the voltage across R
or discharge current faults, or battery pack-short faults.
The MAX1894/MAX1924 provide overvoltage protection
to avoid overcharging cells. When an overvoltage fault
is detected in four consecutive samples, CGO and TKO
go high, stopping the charging process. The
MAX1894/MAX1924 continue to sample the cell volt-
ages, and if no overvoltage is detected, CGO and TKO
SRC
> V
_______________________________________________________________________________________
B4P
Detailed Description
Advanced Li+ Battery-Pack Protectors
+ 0.1V) and the pack voltage is
Protection Features
Modes of Operation
Overvoltage Protection
SRC
is less than the pack
Shutdown Mode
Normal Mode
SENSE
for charge
CC
pin
are returned to the normal low state (see Figure 3). The
MAX1924 also includes a hysteresis of 200mV.
The overvoltage threshold is preprogrammed and
requires no external components. The overvoltage thresh-
old is factory set at 4.25V (typ) for the MAX1894 and
4.35V (typ) for the MAX1924. Contact Maxim for more
information on threshold levels between 4V and 4.4V.
The MAX1894/MAX1924 provide undervoltage protec-
tion to avoid overdischarging the cells. With no battery
charger present, and an undervoltage fault is detected
in four consecutive samples, DSO, CGO, and TKO go
high and the device goes into shutdown mode (see
Figure 4).
If a battery charger is applied to the battery pack and
one or more cells are below V
goes low, allowing trickle-charge current to flow. If no
undervoltage is detected in any sample, DSO, CGO,
and TKO all go low.
The undervoltage threshold is preprogrammed at 2.30V
(typ). Contact Maxim for more information on threshold
levels between 2V and 3.2V.
The MAX1894/MAX1924 protect against excessive
charge current by monitoring the voltage developed
across R
PKN. If V
threshold (V
the charge current comparator is tripped, setting CGO
and TKO high.
The charge-current fault condition is latched and is not
reset until the MAX1894/MAX1924 detect a reversal in
Table 1. Flow Chart Symbol Table
SYMBOL
V
V
V
V
V
V
V
RSENSE
OV_HYT
V
OC_TH
OD_TH
UV_TH
OV_TH
PS_TH
OVF
UVF
SRC
SENSE
RSENSE
OC_TH
Charge-Current Fault Protection
. R
Charge-Current Fault Threshold
(Negative Value)
Discharge-Current Fault Threshold
Pack-Short Discharge-Current Fault
Threshold
Undervoltage Threshold
Overvoltage Threshold
MOSFET Common Source Voltage
Sense Resistor Voltage
Overvoltage Threshold Hysteresis
Overvoltage Sample Counter
Undervoltage Sample Counter
SENSE
, typically 100mV) for more than 3ms,
exceeds the charge-current fault
Undervoltage Protection
is connected between BN and
DESCRIPTION
UV_TH
, then only TKO
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