ltc4007eufd-1-trpbf Linear Technology Corporation, ltc4007eufd-1-trpbf Datasheet - Page 10

• Manufacturer Part Number: ltc4007eufd-1-trpbf
• Description: 4a, High Efficiency, Standalone Li-ion Battery Charger
• Manufacturer: Linear Technology Corporation

OPERATIO
LTC4007
Table 1. Truth Table For Indicator States
MODE
Shut down by low adapter voltage
Charging a low bat
Normal charging
Input current limited charging
Charger paused due to thermistor out of range
Shut down by SHDN pin
Terminated by low-battery fault (Note 1)
Timer is reset when FLAG goes low, then
terminates after 1/4 T
Terminated by expired timer
Timer defeated
Shut down by undervoltage lockout
*Most probable condition X = Don’t care, ** Open-drain output HIGH = OPEN with pull-up
a low forward voltage drop from drain to source. If the
voltage between DCIN and CLN drops to less than 25mV,
the input FET is turned off slowly. If the voltage between
DCIN and CLN is ever less than – 25mV, then the input FET
is turned off in less than 10µs to prevent significant
reverse current from flowing in the input FET. In this
condition, the ACP pin is driven low and the charger is
disabled.
Battery Charger Controller
The LTC4007 charger controller uses a constant off-time,
current mode step-down architecture. During normal op-
eration, the top MOSFET is turned on each cycle when the
oscillator sets the SR latch and turned off when the main
current comparator I
MOSFET is off, the bottom MOSFET is turned on until
either the inductor current trips the current comparator
Note 1: If a depleted battery is inserted while the charger is in this state, the
charger must be reset to initiate charging.
10
U
CMP
resets the SR latch. While the top
+ <UVL
<BAT
>BAT
>BAT
>BAT
>BAT
>BAT
>BAT
>BAT
>BAT
DCIN
X
X
SHDN
HIGH
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
X
ACP**
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
X
X
BGATE
I
the equation:
to set the bottom MOSFET on time. The result is a nearly
constant switching frequency over a wide input/output
voltage range. This activity is diagrammed in Figure 1.
TGATE
INDUCTOR
REV
CURRENT
LOBAT
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
t
OFF
X
X
X
or the beginning of the next cycle. The oscillator uses
OFF
OFF
ON
ON
=
FLAG** FAULT**
HIGH*
HIGH*
HIGH*
V
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
V
DCIN
X
X
DCIN
–
•
HIGH*
HIGH*
HIGH*
HIGH*
(from
V
f
HIGH
NTC)
HIGH
HIGH
HIGH
LOW
LOW
OSC
BAT
X
TRIP POINT SET BY ITH VOLTAGE
Figure 1
t
OFF
HIGH*
HIGH*
HIGH
LOW
LOW
LOW
LOW
LOW
LOW
LOW
I
CL
X
Running
Running
Running
Paused
FLAG =
TIMER
STATE
Reset
Reset
Reset
LOW
>T/4
>T/4
after
>T
X
Forced LOW
for Restart)
for Restart
(Faulted)
(Waiting
(Waiting
CHG**
HIGH*
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
LOW
4006 F01
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