8

FN6435.0

February 25, 2008

shows a typical time domain charge current curve vs time

and its accuracy limits for a complete cycle. The accuracy is

compared against the voltage on the IREF pin. Thermal

foldback may affect the charge current curve as well as the

accuracy.

.

Dynamic Power Path Management

The power path management function of the ISL9301

controls the charge current and the system current when

charging with system load. This is based on the available

input current, which is either limited by the IC (800mA) or by

the input power source, whichever is smaller. When the

output voltage drops to the DPPM threshold (4.35V typical),

the dynamic power path management starts to function. The

DPPM control will first allocate the available current to the

system load, using the remaining current to charge the

battery. This is achieved by dynamically reducing the charge

current until VOUT is regulated. In the event that the system

needs more than the available current, VOUT will continue

to drop. When VOUT drops to below the battery voltage, the

DPPM control will turn on the charge control FET, allowing

the battery to supply current to the system load. Thus the

battery may be charged at a current smaller than the

programmed constant current.

Intelligent Timer

The internal timer in the ISL9301 provides a time reference

for the maximum charge time limit. The nominal clock cycle

for the reference time is set by the external resistor

connected between the TIME pin and GND and is given by

Equation 1.

The nominal maximum charge time interval is calculated

based on the assumption that the programmed charge

current is always available during the entire charging cycle.

However, due to the PPM control or due to the current limit

of the input source, or thermal foldback, the actual charge

current maybe reduced during the constant current charge

period. Under such conditions, the Intelligent Timer control

will increase the timeout interval accordingly to allow

approximately the same mAh product as the original timeout

interval at the programmed current.

Thermal Foldback

The thermal foldback function starts to reduce the charge

current when the internal temperature reaches a typical

value of +115°C. When thermal foldback is encountered, the

charge current will be reduced to a value where the die

temperature stops rising.

Figure 5 shows the thermal foldback operation whereas the

current signals at the summing node of the current error

the temperature tracking current generated from the

charge current until the internal temperature reaches

a constant current IR). As a result, the charging current,

die temperature constant at +115°C.

The system output current, however, is not impacted by the

thermal foldback. Thus, when the charge current is reduced

to zero, if the die temperature still rises, the IC will shut down

to prevent damage to the IC.

1.2

0

150

IR EF PIN VO L T A G E ( V )

FIGURE 2. IREF PIN VOLTAGE vs CHARGE CURRERNT

(IREF IS SET TO 150mA. THE DOTTED LINES

SHOW THE UPPER AND LOWER LIMITS OF THE

TOLERANCE)

TIME

TRICKLE

CC

CV

FIGURE 3. CHARGE CURRENT ACCURACY WHEN

ISL9301