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LTC4160/LTC4160-1

41601f

APPLICATIONS INFORMATION

current than is available will not cause the average input

current limit to be violated. It will merely allow the battery

charger to make use of all available power to charge the

battery as quickly as possible, and with minimal dissipa-

tion within the charger.

Battery Charger Stability Considerations

The LTC4160/LTC4160-1’s battery charger contains both a

constant-voltage and a constant-current control loop. The

constant-voltage loop is stable without any compensation

when a battery is connected with low impedance leads.

Excessive lead length, however, may add enough series

inductance to require a bypass capacitor of at least 1μF

from BAT to GND.

High value, low ESR MLCCs reduce the constant-voltage

loop phase margin, possibly resulting in instability. Up

to 22μF may be used in parallel with a battery, but larger

capacitors should be decoupled with 0.2Ω to 1Ω of series

resistance.

Furthermore, a 100μF capacitor in series with a 0.3Ω re-

sistor from BAT to GND is required to prevent oscillation

when the battery is disconnected.

In constant-current mode, the PROG pin is in the feed-

back loop rather than the battery voltage. Because of the

additional pole created by any PROG pin capacitance,

capacitance on this pin must be kept to a minimum. With

no additional capacitance on the PROG pin, the charger

is stable with program resistor values as high as 25k.

However, additional capacitance on this node reduces the

maximum allowed program resistor. The pole frequency at

the PROG pin should be kept above 100kHz. Therefore, if

the PROG pin has a parasitic capacitance, CPROG, the fol-

lowing equation should be used to calculate the maximum

resistance value for RPROG:

kHz C

PROG

≤

100

π ••

Alternate NTC Thermistors and Biasing

The LTC4160/LTC4160-1 provide temperature qualiﬁed

charging if a grounded thermistor and a bias resistor

are connected to NTC. By using a bias resistor whose

value is equal to the room temperature resistance of the

thermistor (R25) the upper and lower temperatures are

pre-programmed to approximately 40°C and 0°C respec-

tively assuming a Vishay Curve 1 thermistor.

The upper and lower temperature thresholds can be ad-

justed by either a modiﬁcation of the bias resistor value

or by adding a second adjustment resistor to the circuit.

If only the bias resistor is adjusted, then either the upper

or the lower threshold can be modiﬁed but not both. The

other trip point will be determined by the characteristics

of the thermistor. Using the bias resistor in addition to an

adjustment resistor, both the upper and the lower tempera-

ture trip points can be independently programmed with

the constraint that the difference between the upper and

lower temperature thresholds cannot decrease. Examples

of each technique are given below.

NTC thermistors have temperature characteristics which

are indicated on resistance-temperature conversion tables.

The Vishay-Dale thermistor NTHS0603N011-N1003F, used

in the following examples, has a nominal value of 100k

and follows the Vishay Curve 1 resistance-temperature

characteristic.

In the explanation below, the following notation is used.

R25 = Value of the thermistor at 25°C

RNTC|COLD = Value of the thermistor at the cold

trip point

RNTC|HOT = Value of the thermistor at the hot

trip point

rCOLD = Ratio of RNTC|COLD to R25

rHOT = Ratio of RNTC|HOT to R25

RNOM – Primary thermistor bias resistor

(see Figure 7)

R1 = Optional temperature range adjustment resistor

(see Figure 8)

The trip points for the LTC4160/LTC4160-1’s temperature

qualiﬁcation are internally programmed at 0.349 • NTCBIAS

for the hot threshold and 0.765 • NTCBIAS for the cold

threshold.

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