LTC4007_15 Datasheet, PDF (10/24 Pages) Linear Technology – 4A, High Effi ciency, Standalone Li-Ion Battery Charger

LTC4007
OPERATION
Table 1. Truth Table For Indicator States
MODE
DCIN
Shut down by low adapter voltage
<BAT
Charging a low bat
>BAT
Normal charging
>BAT
Input current limited charging
>BAT
Charger paused due to thermistor out of range >BAT
SHDN
LOW
LOW
LOW
LOW
LOW
ACP**
LOW
HIGH
HIGH
HIGH
HIGH
LOBAT
LOW
LOW
HIGH
HIGH
X
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
X
HIGH
>BAT LOW
>BAT LOW
X
HIGH
HIGH
X
LOW
HIGH
Terminated by expired timer
>BAT LOW HIGH HIGH
Charge termination defeated
X
X
X
X
Shut down by undervoltage lockout
>BAT + LOW
<UVL
HIGH
HIGH
*Most probable condition X = Don’t care, ** Open-drain output HIGH = OPEN with pull-up
Note 1: If a depleted battery is inserted while the charger is in this state,
the charger must be reset to initiate charging.
FLAG**
HIGH
HIGH*
HIGH
HIGH*
X
HIGH
HIGH*
FAULT**
HIGH
HIGH*
HIGH*
HIGH*
LOW
(from
NTC)
HIGH
LOW
I_CL
LOW
HIGH*
HIGH*
LOW
HIGH
LOW
LOW
LOW HIGH LOW
HIGH HIGH LOW
X
X
X
HIGH HIGH* LOW
TIMER
STATE
Reset
Running
Running
Running
Paused
CHG**
HIGH
LOW
LOW
LOW
LOW
Reset
>T/4
>T/4
after
FLAG =
LOW
>T
X
Reset
HIGH
HIGH
(Faulted)
HIGH
(Waiting for
Restart
HIGH
(Waiting for
Restart
Forced LOW
HIGH*
keep 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
operation, the top MOSFET is turned on each cycle when
the oscillator sets the SR latch and turned off when the
main current comparator I_CMP resets the SR latch. While
the top MOSFET is off, the bottom MOSFET is turned
on until either the inductor current trips the current
comparator I_REV or the beginning of the next cycle. The
oscillator uses the equation:
t_OFF
=
V_DCIN –
V_DCIN •
V_BAT
f_OSC
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.
OFF
TGATE
ON
ON
BGATE
OFF
t_OFF
TRIP POINT SET BY ITH VOLTAGE
INDUCTOR
CURRENT
Figure 1
4006 F01
4007fc
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