LTC4098EUDC-3.6 データシートの表示（PDF） - Linear Technology

部品番号

コンポーネント説明

メーカー

LTC4098EUDC-3.6

USB Compatible Switching Power Manager/LiFePO4 Charger with Overvoltage Protection

Linear Technology 

LTC4098-3.6

APPLICATIONS INFORMATION

are linked. Therefore, only one of the two trip points can

be chosen, the other is determined by the default ratios

designed in the IC. Consider an example where a 70°C

hot trip point is desired.

From the Vishay curve 1 R-T characteristics, aHOT is

0.1753 at 70°C. Using the previous equation, RNOM should

be set to 70.4k. With this value of RNOM, the cold trip point

is 7°C. Notice that the span is now 63°C rather than the

previous 60°C. This is due to the decrease in temperature

gain of the thermistor as absolute temperature increases.

The upper and lower temperature trip points can be inde-

pendently programmed by using an additional bias resistor

as shown in Figure 9b. The following formulas can be used

to compute the values of RNOM and R1:

RNOM

=

αCOLD – αHOT

3.01

• R25

R1= 0.25 • RNOM – αHOT • R25

For example, to set the trip points to 0°C and 70°C with

a Vishay curve 1 thermistor choose:

USB Inrush Limiting

The USB specification allows at most 10µF of downstream

capacitance to be hot-plugged into a USB hub. In most

LTC4098-3.6 applications, 10µF should be enough to

provide adequate filtering on VBUS.

If more capacitance is required, the OVP circuit will provide

adequate soft-connect time to prevent excessive inrush

currents. An additional 22µF on the VBUS pin will gener-

ally contribute less than 100mA to the hot-plug inrush

current.

Voltage overshoot on VBUS may sometimes be observed

when connecting the LTC4098-3.6 to a lab power supply.

This overshoot is caused by long leads from the power

supply to VBUS. Twisting the wires together from the sup-

ply to VBUS can greatly reduce the parasitic inductance

of these long leads, and keep the voltage at VBUS to safe

levels. USB cables are generally manufactured with the

power leads in close proximity, and thus fairly low parasitic

inductance.

RNOM

=

3.26 – 0.1753

3.01

• 100k

=

102.5k

the nearest 1% value is 102k:

R1 = 0.25 • 102k – 0.1753 • 100k = 7.97k

the nearest 1% value is 8.06k. The final circuit is shown

in Figure 9b and results in an upper trip point of 70°C and

a lower trip point of 0°C.

409836f

25

Share Link: