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MAX8844ZETD+T

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
MAX8844Z/MAX8844Y
impedance during shutdown. When interfacing with a
microprocessor logic input, a pullup resistor to the
microprocessor’s I/O voltage may be required. If
DETBAT is not used, connect DETBAT to GND for nor-
mal operation.
Autobooting Assistant
The MAX8844Z/MAX8844Y contain an autobooting
assistant circuit that generates an enable signal for sys-
tem booting (ABO, ABO). For the MAX8844Z, the boot-
ing assistant functions as an internal OR gate (Figure 1).
The first input is dependent on the input supply voltage
(V
IN
or V
USB
) and DETBAT while the second input is an
external signal applied to ABI. The first input (POK) is dri-
ven high once DETBAT is pulled low through a resistor
less than 51kΩ, 2.35V ≤ (V
IN
or V
USB
) ≤ 7V, and [(V
IN
or
V
USB
) - V
BATT
] ≥ 40mV (typ V
IN
rising).
The second input signal (ABI) is driven by an external
source (Table 1). ABI enables an autoboot signal when
a battery is connected at BATT and is independent of
POK. If POK is pulled low, the booting assistant always
drives ABO high regardless of ABI. ABI is pulled to
GND through an internal 200kΩ resistor. If ABI is sup-
plied from an outside exposed pin, an RC filter (Figure
4) is required for ESD protection and noise filtering. If
ABI is supplied by a system’s internal GPIO, or logic,
the RC filter is not required.
For the MAX8844Y, the output ABO is only dependent
on the state of ABI (Table 1).
CHG
Charge Indicator Output
CHG is an open-drain output that indicates charge sta-
tus. Table 2 describes the state of CHG during different
stages of operation. CHG is suitable for driving a
charge indication LED. If the MAX8844Z/MAX8844Y are
used in conjunction with a microprocessor, a pullup
resistor to the logic I/O voltage allows CHG to indicate
charge status to the microprocessor instead of driving
an LED.
Thermal Regulation
The thermal-regulation loop limits the MAX8844Z/
MAX8844Y die temperatures to +115°C by reducing the
charge current as necessary. This feature not only pro-
tects the IC from overheating, but also allows a higher
charge current without risking damage to the system.
28V Dual Input Linear Li+ Battery Chargers with
Battery Detection and Overvoltage-Protected Output
10 ______________________________________________________________________________________
ABI BATT POK CHARGER STATE
ABO
(MAX8844Z)
ABO
(MAX8844Y)
Low Present High-Z Shutdown Low High-Z
High Present High-Z Shutdown High Low
Low Not present Low CC/CV mode High High-Z
Low Present Low Fast-charge/top-off High High-Z
High Present Low Fast-charge/top-off High Low
Table 1. Autobooting Output States
EN V
IN
*V
BATT
I
BATT
CHG STATE
High X X 0 High-Z Disabled
> 7.5V X
Low
X> V
IN
* - 30mV
0 High-Z Shutdown
Low 4.25V ≤ V
IN
* ≤ 7.5V < 2.4V
10% of
I
FAST-CHARGE
†
Low Precharge
Low 4.25V ≤ V
IN
* ≤ 7.5V ≥ 2.5V 100% of I
FAST-CHARGE
† Low Fast-charge
Low 4.25V ≤ V
IN
* ≤ 7.5V 4.2V < I
MIN
High-Z Top-off
Table 2. CHG States
X = Don’t care.
*
V
IN
and V
USB
are interchangeable. See the DC and USB Power Supplies section.
†
I
FAST-CHARGE
is reduced as necessary to prevent the die temperature from exceeding +115°C.
Note: Present indicates that V
BATT
≥
2.0V and Not Present indicates that the battery is not connected.
Charger Enable Input
The MAX8844Z/MAX8844Y contain an active-low logic
input (EN) used to enable the chargers. Drive EN low,
leave unconnected, or connect to GND to enable the
charge-control circuitry. Drive EN high to disable the
charger-control circuitry. EN has an internal 200kΩ pull-
down resistor.
Soft-Start
The soft-start algorithm activates when entering fast-
charge mode. When the prequalification state is com-
plete (V
BATT
exceeds +2.5V), the charging current
ramps up in 250µs to the full charging current. This
reduces the inrush current demand on the input supply.
Applications Information
Fast-Charge Current Setting
The maximum charging current is programmed by an
external resistor connected from SETI to GND (R
SETI
).
Use the following equation to determine the fast-charge
current (I
FAST-CHARGE
):
where I
FAST-CHARGE
is in amps and R
SETI
is in ohms.
R
SETI
must always be 1.25kΩ or higher due to the con-
tinuous charging current limit of 1A
RMS
.
Top-Off Current Threshold Setting
The top-off current threshold is programmed by an
external resistor connected from MIN to GND (R
MIN
).
Use the following equation to determine the top-off cur-
rent (I
MIN
):
I
MIN
(falling) = 126V/R
MIN
(kΩ) + 27mA
I
MIN
(rising) = 248V/R
MIN
(kΩ) - 16mA
where I
MIN
is in mA and R
MIN
is in kΩ. Use R
MIN
≤
2.2kΩ.
Capacitor Selection
Connect a ceramic capacitor from BATT to GND for
proper stability. Use a 2.2µF ceramic capacitor for most
applications. Connect 1µF ceramic capacitors from IN
to GND and from USB to GND. A larger input capacitor
can be used for high charging current to reduce input
voltage ripple.
Connect 1µF ceramic capacitors from SAFEOUT to
GND and from SAFEUSB to GND. A larger bypass
capacitor for SAFEOUT and SAFEUSB 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.
Thermal Considerations
The MAX8844Z/MAX8844Y are available in a thermally
enhanced TDFN package with an exposed pad.
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.
I
V
R
FAST CHARGE
SETI
-
=
1250
MAX8844Z/MAX8844Y
28V Dual Input Linear Li+ Battery Chargers with
Battery Detection and Overvoltage-Protected Output
______________________________________________________________________________________ 11
IN USB CHARGER STATE
4.25V ≤ V
IN
≤ 7V 4.25V ≤ V
USB
≤ 7V Enabled, selects IN power supply
4.25V ≤ V
IN
≤ 7V Not present Enabled, selects IN power supply
Not present 4.25V ≤ V
USB
≤ 7V Enabled, selects USB power supply
V
IN
≥ 7.5V 4.25V ≤ V
USB
≤ 7V Disabled
4.25V ≤ V
IN
≤ 7V V
USB
≥ 7.5V Enabled
Table 3. Input Power-Supply Selection
MAX8844Z/MAX8844Y
DC and USB Power Supplies
The MAX8844Z/MAX8844Y operate from well-regulated
DC sources and automatically select between both
input power supply connections (Table 3). If both
sources are present at the same time, highest priority is
given to the IN source. The IN source is selected to
ensure the shortest charging time for the system since
it is able to deliver the highest current. The USB fast-
charge current is fixed at 380mA (MAX8844Z) and
450mA (MAX8844Y).
The full charging input voltage range for IN and USB is
4.25V to 7.5V. The device can withstand up to 28V on
both inputs, IN and USB, without damage to the IC. If
V
IN
or V
USB
is greater than 7.5V, the internal overvolt-
age-protection circuitry disables charging until the
input falls below 7.5V. The power supplies must provide
at least 4.25V at the desired peak charging current and
stay below 7V when unloaded.
Typical Application Circuits
AC Adapter Application
Figure 3 shows the MAX8844Z as a Li+ battery charger
with an AC adapter. The MAX8844Z 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 and enables the power sup-
plies of the system to boot up. The MAX8844Z 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
MAX8844Z also provides an overvoltage-protected
SAFEOUT and SAFEUSB to the system.
Factory System Interface Connector Application
Figure 4 shows the MAX8844Z as an autoboot assistant
with the factory system interface connector. The
MAX8844Z detects the ABI input even though there is
no input voltage available and drives ABO high to turn
28V Dual Input Linear Li+ Battery Chargers with
Battery Detection and Overvoltage-Protected Output
12 ______________________________________________________________________________________
VCHG
VBUS
GPIO
GPIO
GPIO
POWER
SUPPLY
ON
SYSTEM
4.2V Li+
POK
V
I/O
CHG
AC ADAPTER
R
SETI
2.8k
Ω
C
BATT
2.2μF
C
SAFEOUT
1μF
R
CHG
1MΩ
R
POK
1MΩ
EN
EP
GND
MIN
R
MIN
1.75kΩ
BATT
DETBAT
SAFEOUT
C
SAFEUSB
1μF
SAFEUSB
IN
ABI
ABO
SETI
MAX8844Z
C
IN
1μF
GND
C
USB
1μF
USB
IF THE POWER SUPPLY
IS ACTIVE-LOW ENABLED,
USE THE MAX8844Y.
Figure 3. AC Adapter Application
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

MAX8844ZETD+T

Mfr. #:
Buy MAX8844ZETD+T
Manufacturer:
Maxim Integrated
Description:
Battery Management 28V Linear Li+ Battery Charger
Lifecycle:
New from this manufacturer.
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