LTC4098EUDC-1 查看數據表（PDF） - Linear Technology

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LTC4098EUDC-1

USB Compatible Switching Power Managers/Li-Ion Chargers with Overvoltage Protection

Linear Technology 

LTC4098/LTC4098-1

APPLICATIONS INFORMATION

Reverse Voltage Protection

The LTC4098/LTC4098-1 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 volt-

age protection up to MN1’s BVDSS and reverse voltage

protection up to MP1’s BVDSS.

USB/WALL

ADAPTER

MP1

MN1

D1

R1

R2

VBUS

C1

LTC4098/

LTC4098-1

OVGATE

OVSENS

VBUS POSITIVE PROTECTION UP TO BVDSS OF MN1

VBUS NEGATIVE PROTECTION UP TO BVDSS OF MP1

40981 F08

Figure 8. Dual-Polarity Voltage Protection

Alternate NTC Thermistors and Biasing

The LTC4098/LTC4098-1 provide 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 40°C and 0°C, re-

spectively (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 thermistor at the cold trip point

RNTC|HOT = Value of 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 9a)

R1 = Optional temperature range adjustment resistor

(see Figure 9b)

The trip points for the LTC4098/LTC4098-1’s temperature

qualification are internally programmed at 0.349 • NTCBIAS

for the hot threshold and 0.765 • NTCBIAS for the cold

threshold.

Therefore, the hot trip point is set when:

RNTC|HOT • NTCBIAS = 0.349 • NTCBIAS

RNOM + RNTC|HOT

and the cold trip point is set when:

RNTC|COLD • NTCBIAS = 0.765 • NTCBIAS

RNOM + RNTC|COLD

Solving these equations for RNTC|COLD and RNTC|HOT

results in the following:

RNTC|HOT = 0.536 • RNOM

and

RNTC|COLD = 3.25 • RNOM

By setting RNOM equal to R25, the previous equations

result in rHOT = 0.536 and rCOLD = 3.25. Referencing these

ratios to the Vishay Resistance-Temperature Curve 1 chart

gives a hot trip point of about 40°C and a cold trip point

of about 0°C. The difference between the hot and cold trip

points is approximately 40°C.

40981fc

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