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LTC4100

sn4100 4100is

Table 6. ILIM Trip Points and Ranges

EXTERNAL

CONTROLLED

RESISTOR

CHARGING

(RILIM)ILIM VOLTAGE

CURRENT RANGE GRANULARITY

Short to GND

VILIM < 0.09VDD

0 < I < 1023mA

1mA

10k

±1%

0.17VVDD < VILIM

0 < I < 2046mA

2mA

< 0.34VVDD

33k

±1%

0.42VVDD < VILIM

0 < I < 3068mA

4mA

< 0.59V

Open (>250k,

0.66VVDD < VILIM

0 < I < 4092mA

4mA

or Short to VDD)

The VLIM Decoder Block

The value of an external resistor connected from this pin

to GND determines one of five voltage limits that are

applied to the charger output value. These limits provide

a measure of safety with a hardware restriction on charg-

ing voltage which cannot be overridden by software.

Table 7. VLIM Trip Points and Ranges (See Figure 5)

EXTERNAL

CONTROLLED

RESISTOR

CHARGING VOLTAGE

(RVLIM)VLIM VOLTAGE

(VOUT) RANGE

GRANULARITY

Short to

VVLIM < 0.09VVCCP

2900mV < VOUT

16mV

GND

< 8800mV

10k

±1%

0.17VVDD < VVLIM

2900mV < VOUT

16mV

< 0.34VVDD

< 13.104mV

33k

±1%

0.42VVCCP < VVLIM

2900mV < VOUT

16mV

< 0.59VVDD

< 17.408mV

100k

±1%

0.66VVDD < VVLIM

2900mV < VOUT

16mV

< 0.84VVDD

< 21.712mV

Open or

0.91VVDD < VVLIM

2900mV < VOUT

16mV

Tied to VDD

< 28000mV

The Voltage DAC Block

Note that the charger output voltage is offset by VREF.

Therefore, the value of VREF is subtracted from the SMBus

ChargingVoltage() value in order for the output voltage to

be programmed properly (without offset). If the

ChargingVoltage() 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

ChargingVoltage() value is above the limit set by the VLIM

pin, then the charger output voltage is set to the value

determined by the VLIM resistor and the VOLTAGE_OR bit

is set. These limits are demonstrated in Figure 6.

OPERATIO

Table 4. SafetySignal State Ranges

SafetySignal

CHARGE

RESISTANCE

STATUS BITS

DESCRIPTION

Ω to 500Ω

RES_UR,

Underrange

RES_HOT

BATTERY_PRESENT

500

Ω to 3kΩ

RES_HOT

Hot

BATTERY_PRESENT

Ω to 30kΩ

BATTERY_PRESENT

Ideal

30k

Ω to 100kΩ

RES_COLD

Cold

BATTERY_PRESENT

Above 100k

Ω

RES_OR

Overrange

RES_COLD

Note: The underrange detection scheme is a very important feature of the

LTC4100. The RTHA/RSafetySignal divider trip point of 0.333 • VDD (1V) is

well above the 0.047 • VDD (140mV) threshold of a system using a 10k

pull-up. A system using a 10k pull-up would not be able to resolve the

important underrange to hot transition point with a modest 100mV of

ground offset between battery and SafetySignal detection circuitry. Such

offsets are anticipated when charging at normal current levels.

The required values for RTHA and RTHB are shown in

Table 5.

Table 5. SafetySignal External Resistor Values

EXTERNAL RESISTOR

VALUE (

Ω)

RTHA

1130

±1%

RTHB

54.9k

±1%

CSS represents the capacitance between the SafetySignal

and GND. CSS may be added to provide additional noise

immunity from transients in the application. CSS can not

exceed 1nF if the LTC4100 is to properly sense the value

of RSafetySignal.

The ILIM 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 charg-

ing current which cannot be overridden by software.

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