MAX8845Z Maxim Integrated Products, MAX8845Z Datasheet - Page 10

• Manufacturer Part Number: MAX8845Z
• Description: 28V Linear Li+ Battery Chargers
• Manufacturer: Maxim Integrated Products

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28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
Connect a ceramic capacitor from BATT to GND for
proper stability. Use a 2.2µF ceramic capacitor for most
applications. Connect a 1µF ceramic capacitor from IN
to GND. A larger input capacitor can be used for high
charging current to reduce input voltage ripple.
Connect a 1µF ceramic capacitor from SAFEOUT to
GND. A larger bypass capacitor for SAFEOUT can be
used for optimum noise immunity. Ceramic capacitors
with X5R or X7R dielectric are highly recommended
due to their small size, low ESR, and small temperature
coefficients.
The MAX8845Z/MAX8845Y are available in thermally
enhanced Thin QFN packages with exposed pads.
Connect the exposed pad to a large copper ground
plane to provide a thermal contact between the device
and the circuit board for increased power dissipation.
The exposed pad transfers heat away from the device,
allowing the IC to charge the battery with maximum cur-
rent, while minimizing the increase in die temperature.
The MAX8845Z/MAX8845Y operate from well-regulated
DC sources. The full charging input voltage range is
4.25V to 7.5V. The device can withstand up to 28V on
the input without damage to the IC. If V
than 7.5V, the internal overvoltage-protection circuitry
disables charging until the input falls below 7.5V. An
appropriate power supply must provide at least 4.25V
at the desired peak charging current and stay below 7V
when unloaded.
Figure 3 shows the MAX8845Z as a Li+ battery charger
with an AC adapter. The MAX8845Z detects the pres-
ence of an input supply and DETBET, resulting in POK
pulled low. Once POK is pulled low, the autobooting
assistant drives ABO high (MAX8845Z) and enables the
power supplies of the system to boot up. The
MAX8845Z begins charging the battery when EN is low
or unconnected. By monitoring CHG, the system can
detect the top-off threshold and terminate the charge
through EN. The MAX8845Z/MAX8845Y also provide an
overvoltage-protected SAFEOUT to the system.
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Typical Application Circuits
Thermal Considerations
Capacitor Selection
AC Adapter Application
DC Input Sources
IN
is greater
Figure 4 shows the MAX8845Z as an autoboot assistor
with the factory system interface connector. The
MAX8845Z detects the ABI input even though there is no
input voltage available and generates an ABO signal to
turn on power supplies to boot up the system. The con-
figuration in Figure 4 is used for system development,
testing, and calibrations in production or design stage.
The universal serial bus (USB) provides a high-speed
serial communication port as well as power for the
remote device. The MAX8845Z/MAX8845Y can be con-
figured to charge batteries at the highest current possi-
ble from the host port. Figure 5 shows the MAX8845Z
as a USB battery charger. To make the circuit compati-
ble with either 100mA or 500mA USB ports, the circuit
initializes at 100mA charging current. The microproces-
sor then enumerates the host to determine its current
capability. If the host port is capable, the charging cur-
rent is increased to 450mA to avoid exceeding the
500mA USB specification through GPIO control. The
MAX8845Z/MAX8845Y also provide an overvoltage-
protected SAFEOUT to the system.
Place all bypass capacitors for IN, BATT, and
SAFEOUT as close as possible to the device. Connect
the battery to BATT as close as possible to the device
to provide accurate battery voltage sensing. Provide a
large copper ground plane to allow the exposed pad to
sink heat away from the device. Make all high-current
traces short and wide to minimize voltage drops. A
sample layout is available in the MAX8845Z Evaluation
Kit to speed designs.
Factory System Interface Connector Application
Recommended PCB Layout and Routing
USB-Powered Li-Ion Charger