LTC4098EUDC-3.6 查看數據表（PDF） - Linear Technology

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LTC4098EUDC-3.6

USB Compatible Switching Power Manager/LiFePO4 Charger with Overvoltage Protection

Linear Technology 

LTC4098-3.6

APPLICATIONS INFORMATION

Reverse Voltage Protection

The LTC4098-3.6 can also be easily protected against the

application of reverse voltage, as shown in Figure 8. D1

and R1 are necessary to limit the maximum VGS seen by

MP1 during positive overvoltage events. D1’s breakdown

voltage must be safely below MP1’s BVGS. The circuit

shown in Figure 8 offers forward voltage protection up

to MN1’s BVDSS and reverse voltage protection up to

MP1’s BVDSS.

USB/WALL

ADAPTER

MP1

MN1

D1

VBUS

C1

LTC4098-3.6

R1

R2

VBUS POSITIVE PROTECTION UP TO BVDSS OF MN1

VBUS NEGATIVE PROTECTION UP TO BVDSS OF MP1

OVGATE

OVSENS

409836 F08

Figure 8. Dual-Polarity Voltage Protection

Alternate NTC Thermistors and Biasing

The LTC4098-3.6 provides temperature-qualified charging

if a grounded thermistor and a bias resistor are connected

to NTC and NTCBIAS. By using a bias resistor whose

value is equal to the room temperature resistance of the

thermistor (R25) the upper and lower temperatures are

preprogrammed to approximately 60°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 follow.

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 thermistor at the cold trip point

RNTC|HOT = Value of thermistor at the hot trip point

aCOLD = Ratio of RNTC|COLD to R25

aHOT = Ratio of RNTC|HOT to R25

RNOM = Primary thermistor bias resistor (see Figure 9a)

R1 = Optional temperature range adjustment resistor

(see Figure 9b)

The trip points for the LTC4098-3.6’s temperature quali-

fication are internally programmed at 0.199 • NTCBIAS

for the hot threshold and 0.765 • NTCBIAS for the cold

threshold.

Therefore, the hot trip point is set when:

RNTC|HOT

• NTCBIAS = 0.199 • NTCBIAS

RNOM + RNTC|HOT

and the cold trip point is set when:

RNTC|COLD • NTCBIAS = 0.765 • NTCBIAS

RNOM + RNTC|COLD

409836f

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