LTC3550EDHC-1#TR Linear Technology, LTC3550EDHC-1#TR Datasheet - Page 12

• Manufacturer Part Number: LTC3550EDHC-1#TR
• Description: IC,Battery Management,CMOS,LLCC,16PIN,PLASTIC
• Manufacturer: Linear Technology
• Type: Battery Chargerr

Specifications of LTC3550EDHC-1#TR

• Battery Type: Li-Ion
• Output Current: 800mA
• Output Voltage: 4.2V
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -40C to 85C
• Mounting: Surface Mount
• Pin Count: 16
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

OPERATIO
LTC3550-1
The LTC3550-1 consists of two main blocks: a lithium-ion
battery charger and a high-effi ciency buck converter that
can be powered from the battery. The charger is designed
to effi ciently manage charging of a single-cell lithium-ion
battery from two separate power sources: a wall adapter
and USB power bus. The internal P-channel MOSFETs
can supply up to 950mA from the wall adapter source
and 500mA from the USB power source. The fi nal fl oat
voltage accuracy is ±0.6%.
The buck converter uses a constant frequency, current
mode step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET) switches
for the buck converter are internal. The LTC3550-1 requires
no external diodes or sense resistors.
Lithium-Ion Battery Charger
A charge cycle begins when the voltage at either the DCIN
pin or USBIN pin rises above the UVLO threshold level and
the charger is enabled through the ENABLE pin. The “on”
state of this pin depends on which source is supplying
power. When the wall adapter input (DCIN) is supply-
ing power, logic low enables the charger and logic high
disables it (a 2MΩ pulldown defaults the charger to
the charging state). The opposite is true when the USB
12
ENABLE
DRIVEN LOW
BAT < 4.1V
U
IN VOLTAGE MODE
I
BAT
< I
CHRG STATE: PULLDOWN
TERMINATE
NO CHARGE CURRENT
I
DCIN
CHRG STATE: Hi-Z
CHRG STATE: Hi-Z
FULL CURRENT
SHUTDOWN
DROPS TO 20µA
STANDBY
CHARGE
MODE
MODE
MODE
Figure 1. LTC3550-1 State Diagram of a Charge Cycle
DCIN POWER APPLIED
DCIN POWER
REMOVED
ENABLE
DRIVEN HIGH
DCIN POWER
REMOVED
POWER SELECTION
STARTUP
input (USBIN) is supplying power; logic low disables the
charger and logic high enables it (the default is the
shutdown state). The DCIN input draws 20µA when the
charger is in shutdown. The USBIN input draws 18µA dur-
ing shutdown if no power is applied to DCIN, but draws
only 10µA when V
Once the charger is enabled, it enters constant-current
mode, where the programmed charge current is supplied
to the battery. When the BAT pin approaches the fi nal
fl oat voltage (4.2V), the charger enters constant-voltage
mode and the charge current begins to decrease. Once
the charge current drops below the programmed termina-
tion threshold (set by the external resistor R
internal P-channel MOSFET is shut off and the charger
enters standby mode.
In standby mode, the charger sits idle and monitors the
battery voltage using a comparator with a 6ms fi lter time
(t
battery voltage falls below 4.1V (which corresponds to ap-
proximately 80% to 90% battery capacity). This ensures
that the battery is kept near a fully charged condition and
eliminates the need for periodic charge cycle initiations.
Figure 1 uses a state diagram to describe the behavior of
the LTC3550-1 battery charger.
RECHRG
REMOVED OR DCIN
POWER APPLIED
ENABLE
DRIVEN LOW
USBIN POWER
REMOVED OR
DCIN POWER
APPLIED
USBIN POWER
ONLY USB POWER APPLIED
). A charge cycle automatically restarts when the
CHRG STATE: PULLDOWN
I
NO CHARGE CURRENT
USBIN
DCIN
CHRG STATE: Hi-Z
CHRG STATE: Hi-Z
FULL CURRENT
SHUTDOWN
DROPS TO 18µA
STANDBY
CHARGE
MODE
MODE
MODE
> V
I
IN VOLTAGE MODE
BAT
USBIN
< I
TERMINATE
3550-1 F01
.
ENABLE
DRIVEN HIGH
BAT < 4.1V
ITERM
), the
35501f