MAX8677AETG+T Maxim Integrated Products, MAX8677AETG+T Datasheet - Page 14
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MAX8677AETG+T
Manufacturer Part Number
MAX8677AETG+T
Description
IC USB/AC ADP CHARGER 24-TQFN
Manufacturer
Maxim Integrated Products
Datasheet
1.MAX8677AETG.pdf
(21 pages)
Specifications of MAX8677AETG+T
Function
Charge Management
Battery Type
Lithium-Ion (Li-Ion)
Voltage - Supply
4.1 V ~ 6.6 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
24-TQFN Exposed Pad
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
The input voltage limiter is essentially an LDO regulator
designed to run in dropout. While in dropout, the regu-
lator dissipates a small I
FET (Q1, Figure 4) between DC and SYS. With an AC
adapter or USB source connected, the input limiter dis-
tributes power from the external power source to the
system load and battery charger. In addition to the
input limiter’s primary function of passing power to the
system and charger loads at SYS, it performs several
additional functions to optimize use of available power:
•
•
Table 2. Input Limiter Control Logic
* Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load
exceeds the input current limit.
14
AC adapter at DC input
USB power at DC input
USB power at USB input;
DC unconnected
DC and USB unconnected
Input Voltage Limiting. If an input voltage is above
the overvoltage threshold (6.9V typ), the MAX8677A
enters overvoltage lockout (OVLO). OVLO protects
the MAX8677A and downstream circuitry from high-
voltage stress up to 14V at DC and 8V at USB. In
OVLO, VL remains on, the input switch that sees
overvoltage (Q1, Q3, Figure 4) opens, and the
appropriate power-monitor output (DOK, UOK) is
high impedance, and CHG is high impedance.
If both DC and USB see overvoltage, both input
switches (Q1 and Q2, Figure 4) open and the
charger turns off. The BAT-SYS switch (Q3, Figure
4) closes, allowing the battery to power SYS.
An input is also invalid if it is less than BAT, or less
than the DC undervoltage threshold of 3.5V (falling).
With an invalid input voltage, SYS connects to BAT
through a 40mΩ switch (Q3, Figure 4).
Input Overcurrent Protection. The current at DC
and USB is limited to prevent input overload. This cur-
rent limit can be selected to match the capabilities of
the source, whether it is a 100mA or 500mA USB
source, or an AC adapter. When the load exceeds
the input current limit, SYS drops to 68mV below BAT
and the battery supplies supplemental load current.
______________________________________________________________________________________
POWER SOURCE
2
R loss through the 0.2Ω MOS-
DOK
H
H
H
H
L
L
L
L
UOK
Input Limiter
H
X
X
X
X
L
L
L
PEN1
H
X
X
X
X
L
L
L
PEN2
H
H
X
X
X
X
L
L
•
•
The input and charger current limits are set as shown in
Table 2. It is often preferable to change the input cur-
rent limit as the input power source is changed. The
MAX8677A facilitates this by allowing different input
current limits for DC and USB as shown in Table 2.
Thermal Limiting. The MAX8677A reduces input lim-
iter current by 5%/°C when its die temperature
exceeds +100°C. The system load (SYS) has priority
over the charger current, so input current is first
reduced by lowering charge current. If the junction
temperature still reaches +120°C in spite of charge-
current reduction, no input (DC or USB) current is
drawn, the battery supplies the entire system load, and
SYS is regulated at 68mV below BAT. Note that this
on-chip thermal-limiting circuitry is not related to and
operates independently from the thermistor input.
Adaptive Battery Charging. While the system is
powered from DC, the charger draws power from
SYS to charge the battery. If the charger load plus
system load exceeds the input current limit, an
adaptive charger control loop reduces charge cur-
rent to prevent the SYS voltage from collapsing.
Maintaining a higher SYS voltage improves efficien-
cy and reduces power dissipation in the input limiter.
The total current through the switch (Q1 or Q2 in
Figure 4) is the sum of the load current at SYS and
the battery charging current. The limiter clamps at
5.3V, so input voltages greater than 5.3V can
increase power dissipation in the limiter. The limiter
power loss is (V
0.2Ω. Also note that the MAX8677A turns off any
input that exceeds 6.9V (nominal).
USUS
H
H
X
X
L
L
L
L
USB suspend
No DC input
3000/R
CURRENT
DC INPUT
DC and USB Connections and
100mA
500mA
LIMIT
DC
PSET
- 5.3) x I, but not less than I
Current-Limit Options
USB input off;
USB suspend
No USB input
DC input has
USB INPUT
CURRENT
100mA
500mA
priority
LIMIT
Input Current Limit
CURRENT*
MAXIMUM
3000/R
3000/R
CHARGE
100mA
500mA
0
0
0
ISET
ISET
2
x