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PDF MAX1874 Data sheet ( Hoja de datos )
| Número de pieza | MAX1874 | |
| Descripción | Dual-Input / USB/AC Adapter / 1-Cell Li+ Charger with OVP and Thermal Regulation | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2912; Rev 0; 7/03
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
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
Pin Configuration
TOP VIEW
16 15 14 13
DCLV
DC
CHG
USEL
1
2
3
4
MAX1874
12 USB
11 BYP
10 PGND
9 REF
5678
Features
o Charge from USB* or AC Adapter
o Automatic Switchover to AC Adapter
o Thermal Limiting Simplifies Board Design
o Small, High-Power 16-Pin Thin QFN Package
o Input Protection Up to 18V
o Soft-Start
o Automatic Battery-to-Input Load Switch
*Protected by U.S. Patent #6,507,172.
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX1874ETE -40°C to +85°C 16 Thin QFN 5mm x 5mm
Typical Operating Circuit
DC INPUT
USB INPUT
TO REF
DC
MAX1874 PON
DCOK
DCLV
BATT
UOK
USB
CHG
USEL
DCI EN
REGULATOR REF
Li+
CELL
500mA
100mA
THRM
NTC
BYP PGND GND THERMISTOR
THIN QFN
5mm x 5mm
Functional Diagram appears at the end of the data sheet.
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = -40°C to +85°C, unless otherwise
noted. Typical values are at TA = +25°C.) (Note 4)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
BATTERY VOLTAGE
BATT Regulation Voltage
BATT Prequal Voltage Threshold
BATT rising
4.1685
2.8
4.2315
3.2
V
V
REF Voltage (Buffered Output)
IREF = 0 to 500µA, 4V < VDC or VUSB < 6.5V;
does not affect BATT regulation accuracy
2.94
3.06 V
BATTERY CHARGING AND PRECHARGE CURRENT
DCI Voltage Range
DCI Voltage to BATT Current
VDCI = VREF
VDCI = VREF / 2
USB Charging Current
USEL = high
USEL = low
Prequal Charging Current
VBATT = 2.5V
BATT Input Current
BATT Shutdown Current
No DC or USB power, VBATT = 4.2V
EN = GND, USB and/or DC powered
0.1 x VREF
930
490
40
VREF
1070
565
495
95
70
7.5
2
V
mA
mA
mA
µA
µA
THERMISTOR MONITOR AND DIE-TEMPERATURE REGULATION
THRM COLD Trip Level
(Note 2)
THRM HOT Trip Level
(Note 2)
THRM Disable Threshold
0.72
0.28
50
0.76
0.30
150
VREF
VREF
mV
LOGIC INPUT/OUTPUTS AND GATE DRIVERS
DCOK Off-Leakage Current
UOK Off-Leakage Current
V DCOK = 12V, VDC = 0V
V UOK = 6.5V
CHG Threshold to Indicate Battery Full,
Battery Current Falling (Note 3)
DC input (% of charge current set at DCI)
USB input, USEL = 5V
(% of USB charging current)
CHG Logic-Low Output
Sinking 10mA sink
CHG Leakage Current
V CHG = 6.5V
EN, USEL Logic-Input High Level
8
20
1.6
1 µA
1 µA
20
%
30
0.4 V
1 µA
V
EN, USEL Logic-Input Low Level
EN, USEL Input Bias Current
0.4 V
1 µA
Note 1: BYP internally connects to the active power input (DCLV or USB). DCLV takes priority if both inputs are powered.
Note 2: These limits guarantee +5°C accuracy with 5% accuracy of thermistor beta (3450 nominal) with 2°C of hysteresis.
Note 3: The CHG output does not go high unless charge current is below the indicated threshold (as set by DCI) and the charger is in
voltage-mode operation. In 100mA USB mode, CHG goes high when the charger transitions from current to voltage mode.
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________ 5
5 Page 
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
acceptable range. To verify that the input voltage is
stable, DCOK has an internal delay of 20ms before con-
necting power to DCLV. DCOK remains operational
when EN is low (charger off).
USB Power-OK (UOK)
UOK is an active-low, open-drain output that goes low
to indicate that VUSB is valid (greater than 4V). UOK
remains operational when EN is low (charger off). An
external 10kΩ pullup resistor keeps UOK high until it is
certain that power is within the acceptable range. UOK
can be used as a logic output, or to control a MOSFET
that switches USB power directly to the system load
when the MAX1874 is powered from a USB source (Q1
in Figure 4).
Bypass (BYP)
BYP is the bypass connection for the MAX1874’s inter-
nal power rail. Bypass to GND with a 2.2µF or greater
capacitor. The voltage at BYP is supplied from either
DCLV or USB through an internal 5Ω switch network.
Power On (PON)
PON goes high when VDC or VUSB is within its normal
operating range. PON can be used as a logic output to
indicate power is connected or can drive an external
P-channel MOSFET that switches the system load from
the battery to an external source when power is applied.
See Q3 in Figures 4 and 5.
Charging Current
Precharge Current
When the MAX1874 is powered with a battery connect-
ed, the IC first detects if the cell voltage is ready for full
charge current. If the cell voltage is less than the pre-
qual level (3V typ), the battery is precharged with a
50mA current until the cell reaches the proper level.
The full charging current, as set by USEL or DCI, is
then applied.
USEL
The charging current from the USB source is selected
by USEL. A USB source can supply a maximum of
100mA or 500mA. USB hosts and powered hubs typi-
cally supply 500mA, while unpowered hubs supply
100mA. A logic low on USEL selects a 100mA maximum
charging current. A logic high on USEL selects a 500mA
maximum charging current.
DCI
When charging from the DCLV input, the voltage at DCI
sets the charge current. The voltage-to-current transfer
ratio from DCI to BATT is 1A/VREF. The DCI pin should
be connected to a resistive divider from REF to DCI to
GND (R5 and R6 in Figures 2 and 4). In this configura-
tion, IBATT is as follows:
IBATT = [R6 / (R5 + R6)] Amps
R5 and R6 should total 25kΩ or more to minimize loading
on REF. Connecting DCI directly to REF results in a 1A
charge current.
Battery Full (CHG)
CHG is low when the MAX1874 is charging in either the
prequal or full-charging state. CHG then goes high
when the charging current falls below a percentage of
the set fast-charge current (Table 2) and the charger is
in voltage mode (VBATT near 4.2V). The CHG current
threshold is a function of the charger mode. When
charging from a DC source, CHG goes high when
IBATT falls to 12.5% of the current set by VDCI and the
charger is in voltage mode (VBATT near 4.2V). When
charging from a USB source with USEL high, CHG
goes high when IBATT falls to 125mA and the charger is
in voltage mode. If the MAX1874 is charging from a
USB source with USEL low, CHG goes high when the
charger enters voltage mode.
Package Thermal Limiting
On-chip thermal limiting in the MAX1874 simplifies PC
board layout and allows charging rates to be automati-
cally optimized without constraints imposed by worst-
case minimum battery voltage, maximum input voltage,
and maximum ambient temperature. When the
MAX1874 thermal limit is reached, the charger does not
shut down but simply reduces charging current. This
allows the board design to be optimized for compact
size and typical thermal conditions. The MAX1874
reduces charging current to keep its die temperature
below +105°C.
Table 2. CHG Battery Full Indication
CHARGING SOURCE
CHARGE CURRENT THRESHOLD FOR CHG GOING HIGH
DCLV Charging
12.5% of Charge Current Set by DCI and Charger in Voltage Mode
USB Charging 500mA (USEL high) 125mA and Charger in Voltage Mode
USB Charging 100mA (USEL low) Charger in Voltage Mode
Note: CHG does not go high when charge current is reduced by the thermal regulation loop.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX1874.PDF ] | |
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