9

LTC4007

4007i

gate of the input FET is driven to a voltage sufficient to 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 10

µs 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

MOSFET is off, the bottom MOSFET is turned on until

either the inductor current trips the current comparator

the equation:

t

VV

Vf

OFF

DCIN

BAT

DCIN

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.

TGATE

OFF

ON

BGATE

INDUCTOR

CURRENT

TRIP POINT SET BY ITH VOLTAGE

ON

OFF

4006 F01

Figure 1

OPERATIO

Table 1. Truth Table For Indicator States

TIMER

MODE

DCIN

SHDN

ACP**

LOBAT

FLAG** FAULT**

STATE

CHG**

Shut down by low adapter voltage

<BAT

LOW

LOW

LOW

HIGH

HIGH

LOW

Reset

HIGH

Charging a low bat

>BAT

LOW

HIGH

LOW

HIGH*

HIGH*

HIGH*

Running

LOW

Normal charging

>BAT

LOW

HIGH

HIGH

HIGH

HIGH*

HIGH*

Running

LOW

Input current limited charging

>BAT

LOW

HIGH

HIGH

HIGH*

HIGH*

LOW

Running

LOW

Charger paused due to thermistor out of range

>BAT

LOW

HIGH

X

X

LOW

HIGH

Paused

LOW

(from

NTC)

Shut down by SHDN pin

X

HIGH

X

X

HIGH

HIGH

LOW

Reset

HIGH

Terminated by low-battery fault (Note 1)

>BAT

LOW

HIGH

LOW

HIGH*

LOW

LOW

>T/4

HIGH

(Faulted)

Timer is reset when FLAG goes low, then

>BAT

LOW

HIGH

HIGH

LOW

HIGH

LOW

>T/4

HIGH

terminates after 1/4 T

after

(Waiting

FLAG =

for Restart)

LOW

Terminated by expired timer

>BAT

LOW

HIGH

HIGH

HIGH

HIGH

LOW

>T

HIGH

(Waiting

for Restart

Timer defeated

XXXXX

XX

X

Forced LOW

Shut down by undervoltage lockout

>BAT

LOW

HIGH

HIGH

HIGH

HIGH*

LOW

Reset

HIGH*

+ <UVL

*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.