MAX1507 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Linear Li+ Battery Charger with Integrated Pass FET and Thermal Regulation in 3mm x 3mm Thin DFN

Linear Li+ Battery Charger with Integrated Pass FET
and Thermal Regulation in 3mm x 3mm Thin DFN
CHG Charge Indicator Output
CHG is an open-drain current source for indicating
charge status. Table 1 describes the state of CHG dur-
ing different stages of operation.
CHG is a nominal 12mA current source suitable for dri-
ving a charge-indication LED. If the MAX1507 is used
in conjunction with a microprocessor, a pullup resistor
to the logic I/O voltage allows CHG to indicate charge
status to the µP instead of driving an LED.
Soft-Start
An analog soft-start algorithm activates when entering
fast-charge mode. When the prequalification state is
complete (V_BATT exceeds +2.5V), the charging current
ramps up in 3ms to the full charging current. This
reduces the inrush current on the input supply.
Applications Information
Charge-Current Selection
The maximum charging current is programmed by an
external R_ISET resistor connected from ISET to GND.
Select the R_ISET value based on the following formula:
I_FAST= 1461V / R_ISETΩ
where I_FAST is in amps and R_ISET is in ohms. ISET can
also be used to monitor the fast-charge current level.
The output current from the ISET pin is 0.958mA per
amp of charging current. The output voltage at ISET is
proportional to the charging current as follows:
V_ISET = (I_CHG x R_ISET) / 1044
The voltage at ISET is nominally 1.4V at the selected
fast-charge current, and falls with charging current as
the cell becomes fully charged.
Thermal-Regulation Selection
Set the regulated die temperature of the MAX1507 with
the TEMP three-level logic input. The MAX1507
reduces the charge current to limit the die temperature
to the value set by TEMP. The MAX1507 operates nor-
mally while the thermal loop is active. An active thermal
loop does not indicate a fault condition. TEMP allows
the MAX1507 to maximize the charge current while pro-
viding protection against excessive power dissipation.
Connect TEMP to GND to regulate the die temperature
at +90°C. Leave TEMP floating to regulate the die tem-
perature at +100°C. Connect TEMP to VL to regulate
the die temperature at +130°C.
Capacitor Selection
Connect a ceramic capacitor from BATT to GND for
proper stability. Use a 1µF X5R ceramic capacitor for
most applications.
Connect a 1µF ceramic capacitor from IN to GND. Use
a larger input bypass capacitor for high input voltages
or high charging currents to reduce supply noise.
Connect a 0.47µF ceramic capacitor from VL to GND.
Thermal Considerations
The MAX1507 is in a thermally enhanced thin DFN
package with exposed paddle. Connect the exposed
paddle of the MAX1507 to a large copper ground plane
to provide a thermal contact between the device and
the circuit board. The exposed paddle transfers heat
away from the device, allowing the MAX1507 to charge
the battery with maximum current, while minimizing the
increase in die temperature.
DC Input Sources
The MAX1507 operates from well-regulated DC
sources. The full-charging input-voltage range is 4.25V
to 7V. The device can stand up to 13V on the input
without damage to the IC. If V_IN is greater than 7V, then
the MAX1507 stops charging.
An appropriate power supply must provide at least
4.25V when sourcing the desired peak charging cur-
rent. It also must stay below 6.5V when unloaded.
Table 1. CHG States
EN
V_IN
X
V_BATT
Low
4.25V ≤ V_IN ≤ 7V
Low
4.25V ≤ V_IN ≤ 7V
Low
4.25V ≤ V_IN ≤ 7V
Low
>7V
V_BATT
V_IN
< 2.5V
≥ 2.5V
4.2V
X
I_BATT
0
10% of I_FAST
I_FAST*
10% of I_FAST
0
CHG
Hi-Z
Low
Low
Hi-Z
Hi-Z
High
X
X
0
Hi-Z
X = Don’t care.
*I_FAST is reduced as necessary to maintain the die temperature set by the TEMP input.
STATE
Shutdown
Prequalification
Fast Charge
Full Charge
Overvoltage
Disabled
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