LTC4160EPDC-PBF View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4160EPDC-PBF

Switching Power Manager with USB On-The-Go And Overvoltage Protection

Linear Technology 

LTC4160/LTC4160-1

APPLICATIONS INFORMATION

Therefore, the hot trip point is set when:

RNTC HOT

• NTCBIAS = 0.349 • NTCBIAS

RNOM + RNTCHOT

And the cold trip point is set when:

RNTCCOLD • 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 above 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.

By using a bias resistor, RNOM, different in value from

R25, the hot and cold trip points can be moved in either

direction. The temperature span will change somewhat

due to the non-linear behavior of the thermistor. The fol-

lowing equations can be used to calculate a new value for

the bias resistor:

RNOM

=

rHOT

0.536

• R25

RNOM

=

rCOLD

3.25

•

R25

where rHOT and rCOLD are the resistance ratios at the de-

sired hot and cold trip points. Note that these equations

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 60°C

hot trip point is desired.

From the Vishay Curve 1 R-T characteristics, rHOT is

0.2488 at 60°C. Using the above equation, RNOM should

24

be set to 46.4k. With this value of RNOM, rCOLD is 1.436

and the cold trip point is about 16°C. Notice that the span

is now 44°C rather than the previous 40°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,

R1, as shown in Figure 8. The following formulas can be

used to compute the values of RNOM and R1:

RNOM

=

rCOLD – rHOT

2.714

• R25

R1= 0.536 • RNOM – rHOT • R25

For example, to set the trip points to 0°C and 45°C with

a Vishay Curve 1 thermistor choose:

RNOM

=

3.266 – 0.4368

2.714

•

100k

=

104.2k

the nearest 1% value is 105k:

R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k

the nearest 1% value is 12.7k. The final solution is shown

in Figure 8 and results in an upper trip point of 45°C and

a lower trip point of 0°C.

NTCBIAS

3

RNOM

100k

NTC

4

LTC4160/LTC4160-1

NTC BLOCK

0.765 • NTCBIAS

–

+

TOO_COLD

T

RNTC

100k

–

0.349 • NTCBIAS +

TOO_HOT

+

0.1V

–

NTC_ENABLE

41601 F07

Figure 7. Standard NTC Configuration

41601f

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