MAX1874ETE Maxim Integrated Products, MAX1874ETE Datasheet - Page 10

• Manufacturer Part Number: MAX1874ETE
• Description: Battery Management Dual-Input USB/AC Adapter 1-Cell Li+
• Manufacturer: Maxim Integrated Products

Specifications of MAX1874ETE

• Battery Type: Li-Ion, Li-Polymer
• Operating Supply Voltage: 4.35 V to 6.5 V
• Supply Current: 4 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TQFN-16
• Charge Safety Timers: No
• Mounting Style: SMD/SMT
• Temperature Monitoring: No

The MAX1874 charges a single-cell Li+ battery from
either USB power sources or AC adapter sources. It
contains a complete two-input linear charger that controls
both battery charge current and voltage. In addition to
all charging functions, the MAX1874 includes voltage-
sensing and switchover circuitry that selects the active
input source. When both inputs are active, priority is
given to the AC adapter (DC). Charging current is regu-
lated with on-chip power MOSFETs, so no external
MOSFETs are required for a basic two-input charger.
Additional features such as input-voltage protection and
battery-load switching can be added with external
MOSFETs that are driven directly from MAX1874 outputs.
The MAX1874 also features a thermal regulation loop
that adjusts charging current so the die temperature
remains below +105°C. See the Package Thermal
Limiting section. This on-chip thermal control simplifies
PCB layout and allows the optimum charging rate to be
set without the thermal limits imposed by worst-case
battery and input voltage. When the MAX1874 thermal
limit is reached, the charger does not shut down but
reduces charging current.
In addition to, and separate from, its internal die tem-
perature control, the MAX1874 can also monitor ambi-
ent or cell temperature with an external thermistor
connected to THRM. When the thermistor temperature
is out of range (greater than +50°C or less than 0°C),
charging stops until the temperature returns to normal.
See the External Thermistor Monitor (THRM) section.
Other features include a CHG output to indicate battery
full (when charge current tapers to a percentage of
fast-charge current). DCOK, UOK, and power-on (PON)
outputs indicate when valid power is present. These
outputs can drive overvoltage protection and power
selection MOSFETs (Figures 3, 4, and 5).
When charging is stopped or input power is removed,
battery leakage is typically 5µA. No input blocking
diodes are required to prevent battery drain.
With USB power connected, but without power at the
DC input, charge current can be set to either 500mA or
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Table 1. USB and DC Input Selection
Note: V
10
Exceeds operating input
range. Not allowed. See the
Absolute Maximum Ratings
section.
V
DC
______________________________________________________________________________________
> 18V OR V
DC
takes precedence when both inputs are valid.
USB
> 6.5V
Detailed Description
DCLV powers device
and supplies charging
current.
4V < V
0 < V
DC
USB
< 6.2V AND
< 6.5V
1)
2)
USB powers device and supplies charging
current.
DCLV disconnected from DC source through
external MOSFET (Q2 Figures 3, 4, and 5).
100mA through the USEL input. When power is taken
from the DC input, charge current is linearly set by the
voltage at DCI. The MAX1874 charge current can also
be DAC controlled with the output of a DAC connected
to DCI. See the Charging Current section.
The enable input, EN, switches the MAX1874 on or off.
With EN high, the MAX1874 is on and can begin charg-
ing. When EN is low, UOK, DCOK, PON, and REF remain
active. Charging stops when EN is low, but the chip
remains biased and continues to draw current from the
input supplies so power-monitoring outputs can remain
valid.
The MAX1874 can charge from either the USB input or
the DC input. It cannot charge from both sources at the
same time. The IC automatically selects the active input
and charges from that. If both power sources are
active, the adapter input (DC) takes precedence. Table
1 describes the switchover between DC and USB.
DC serves as the sense input for the adapter power
source. This input senses when DC is above 6.2V (maxi-
mum range is 18V) or below 4V. When it senses the DC
source is above 6.2V, DCOK goes high, indicating an
invalid DC input. See the DC Power-OK (
When power is connected to DC, the MAX1874 requires
20ms to validate the input. Consequently, charging is
interrupted for 20ms until it is determined that input
power is good. Also, when DC power is removed while
valid USB power is present, charging is interrupted for
20ms before transferring to the USB source.
DCOK is an active-low, open-drain output that goes low
when V
used as a logic output, but is also designed to drive an
external MOSFET (Q2 in Figures 3, 4, and 5). This allows
the charger to protect the input from overvoltage up to
18V. Charging is disabled for inputs over 6.2V. An exter-
nal 1kΩ pullup resistor keeps DCOK high (external
MOSFET off) until it is certain the voltage is within the
V
4V < V
DC
< 4V OR V
DC
USB
is below 6.2V or above 3.5V. DCOK can be
< 6.5V AND
DC
USB-to-Adapter Power Handoff
> 6.2V
DC Power-OK ( DCOK )
No charging
6.2V, AND V
V
DC
DCOK ) section.
Enable (EN)
< 4V OR V
USB
DC
< 4V
>