Rainbow Electronics MAX1874 - Manual

General Description
The MAX1874 charges a single-cell Li+ battery from
both USB and AC adapter sources. It also includes bat-
tery-to-input power switchover, so the system can be
powered directly from the power source rather than
from the battery.
In its simplest application, the MAX1874 needs no
external MOSFET or diodes, and accepts input volt-
ages up to 6.5V; however, DC input overvoltage protec-
tion up to 18V can be added with a single SOT PFET.
On-chip thermal limiting simplifies PC board layout and
allows optimum charging rate 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 simply reduces charging current.
Ambient or battery temperature can be monitored with
an external thermistor. When the temperature is out of
range, charging pauses.
Other features include a CHG output to indicate when
battery current tapers below a predetermined level. DC
power-OK (DCOK), USB power-OK (UOK), and power-
on (PON) outputs indicate when valid power is present.
These outputs drive logic or power-selection MOSFETs
to disconnect the charging sources from the load and
to protect the MAX1874 from overvoltage.
The MAX1874 contains no logic for communication with
the USB host. It must receive instructions from a local
microcontroller. The MAX1874 is available in a 16-pin
5mm
✕ 5mm thin QFN package and operates over the
-40°C to +85°C temperature range.
Applications
PDAs Cell Phones
Wireless Appliances Digital Cameras
Features
♦ Charge from USB* or AC Adapter
♦ Automatic Switchover to AC Adapter
♦ Thermal Limiting Simplifies Board Design
♦ Small, High-Power 16-Pin Thin QFN Package
♦ Input Protection Up to 18V
♦ Soft-Start
♦ Automatic Battery-to-Input Load Switch
*Protected by U.S. Patent #6,507,172.
MAX1874
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2912; Rev 0; 7/03
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX1874ETE -40 °C to +85°C 16 Thin QFN 5mm x 5mm
16 15 14 13
DCOK BATT PON UOK
9
10
11
12
REF
PGND
BYP
USB
4
3
2
1
USEL
CHG
DC
DCLV
5 6 7 8
EN
GND DCI
THRM
MAX1874
THIN QFN
5mm x 5mm
TOP VIEW
Pin Configuration
Functional Diagram appears at the end of the data sheet.
MAX1874
USB INPUT
DC INPUT
TO REF
DCLV
GND
BATT
NTC
THERMISTOR
PON
REF
THRM
DC
USB
Li+
CELL
USEL
500mA
100mA
EN DCI
PGND BYP
REGULATOR
UOK
CHG
DCOK
Typical Operating Circuit