User manual

LTC4100
19
4100fb
OPERATION
The I
LIM
Decoder Block
The value of an external resistor connected from this pin
to GND determines one of four current limits that are used
for maximum charging current value. These limits provide
a measure of safety with a hardware restriction on charging
current which cannot be overridden by software.
Table 6. I
LIM
Trip Points and Ranges
EXTERNAL
RESISTOR
(R
ILIM
)I
LIM
VOLTAGE
CONTROLLED
CHARGING
CURRENT RANGE GRANULARITY
Short to GND V
ILIM
< 0.09V
DD
0 < I < 1023mA 1mA
10k ±1% 0.17V
VDD
<
V
ILIM
< 0.34V
VDD
0 < I < 2046mA 2mA
33k ±1% 0.42V
VDD
<
V
ILIM
< 0.59V
0 < I < 3068mA 4mA
Open (>250k,
or Short to V
DD
)
0.66V
VDD
<
V
ILIM
0 < I < 4092mA 4mA
The V
LIM
Decoder Block
The value of an external resistor connected from this pin
to GND determines one of fi ve voltage limits that are ap-
plied to the charger output value. These limits provide a
measure of safety with a hardware restriction on charging
voltage which cannot be overridden by software.
Table 7. V
LIM
Trip Points and Ranges (See Figure 5)
EXTERNAL
RESISTOR
(R
VLIM
)V
LIM
VOLTAGE
CONTROLLED
CHARGING VOLTAGE
(V
OUT
) RANGE GRANULARITY
Short to
GND
V
VLIM
< 0.09V
VCCP
2900mV < V
OUT
< 8800mV
16mV
10k ±1% 0.17V
VDD
< V
VLIM
< 0.34V
VDD
2900mV < V
OUT
< 13104mV
16mV
33k ±1% 0.42V
VCCP
< V
VLIM
< 0.59V
VDD
2900mV < V
OUT
< 17408mV
16mV
100k ±1% 0.66V
VDD
< V
VLIM
< 0.84V
VDD
2900mV < V
OUT
< 21712mV
16mV
Open or
Tied to V
DD
0.91V
VDD
< V
VLIM
2900mV < V
OUT
< 28000mV
16mV
The Voltage DAC Block
Note that the charger output voltage is offset by V
REF
.
Therefore, the value of V
REF
is subtracted from the SMBus
ChargingVoltage() value in order for the output voltage to
be programmed properly (without offset). If the Charging-
Voltage() value is below the nominal reference voltage of
the charger, nominally 1.184V, the charger output voltage
is programmed to zero. In addition, if the ChargingVolt-
age() value is above the limit set by the V
LIM
pin, then the
charger output voltage is set to the value determined by
the V
LIM
resistor and the VOLTAGE_OR bit is set. These
limits are demonstrated in Figure 6.
PROGRAMMED VALUE (V)
0
CHARGER V
OUT
(V)
25
20
15
10
5
0
10
20
25
4100 F06
5
15
30
35
R
VLIM
= 33k
Figure 6. Transfer Function of Charger
NOTE: THE LTC4100 CAN BE PROGRAMMED WITH ChargingVoltage() FUNCTION VALUES
BETWEEN 1.184V AND 2.9V, HOWEVER, THE BATTERY CHARGER CONTROLLER OUTPUT
VOLTAGE MAY BE ZERO WITH PROGRAMMED VALUES BELOW 2.9V.