7

LTC1729 Series

4.5V/CELL

BATTERY CLAMP

PULL-DOWN

ON

2.7V/CELL

NORMAL CHARGE

TRICKLE CHARGE

PRECONDITIONING

1729 F04

HOLD MODE

2.79V

HOLD MODE

0.2V

RESET MODE

NORMAL CHARGE

0.405V

1729 F05

The logic and timer block consists of a state machine,

oscillator and counter. The state machine will be dis-

cussed in detail in the next section. The oscillator is

internally trimmed to 131kHz. The counter is composed of

a chain of 25 flip-flops that includes self-test circuitry.

State Machine

The state machine is responsible for the following items:

1. When to start and stop the charger. The internal timer

must be initialized every time a new battery is installed

or when the input supply is applied.

2. When a battery is installed, the state machine must

determine if it is a new battery or if the previous battery

has been reinstalled.

Figure 4. BAT Voltage Operating Range

Figure 5. NTC Voltage Operating Range

When the input supply is removed in step-down charger

diode drop below the battery voltage. This is due to the

is present in the LT1510, LT1511, LT1769, and the body

diode of the top MOSFET in the LT1505 charger. Removing

the UVLO threshold, thus shutting down the LTC1729 and

minimizing battery drain. Once the input supply is con-

nected, the LTC1729 resets the timers and begins another

charge cycle. There is a disconnect transistor that will

remove the OVP resistor divider from the battery when the

RESET MODE

STATUS = PULL-DOWN

PAUSE

STATUS = PULL-DOWN

DONE

STATUS = OPEN

NO BAT

STATUS = OPEN

HOLD MODE

STATUS = PREVIOUS STATUS

PRECONDITION

STATUS = PULL-DOWN

1729 F06

NOTE: FOR STATUS

PULL-DOWN = HARD:

FOR CURRENT > C/10

PULL-DOWN = 50

µA:

FOR CURRENT < C/10 FOR 3SEC

FOR MORE THAN 1SEC

FOR MORE THAN 1SEC

FOR MORE THAN 1SEC

FOR MORE THAN 1SEC

CHARGER “ON”

STATUS = PULL-DOWN

CHARGE

Figure 6. State Diagram