LTC3576EUFE#PBF Linear Technology, LTC3576EUFE#PBF Datasheet - Page 38

• Manufacturer Part Number: LTC3576EUFE#PBF
• Description: IC POWER MANAGER W/USB OTG 38QFN
• Manufacturer: Linear Technology

Specifications of LTC3576EUFE#PBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 4.35 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

LTC3576/LTC3576-1
The trip points for the LTC3576/LTC3576-1’s temperature
qualifi cation 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:
And the cold trip point is set when:
Solving these equations for R
results in the following:
and
By setting R
in r
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, R
R25, the hot and cold trip points can be moved in either
direction. The temperature span will change somewhat
due to the nonlinear behavior of the thermistor. The fol-
lowing equations can be used to calculate a new value for
the bias resistor:
where r
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.
APPLICATIONS INFORMATION
38
R
R
R
R
R
R
HOT
NTC|HOT
NTC|COLD
NOM
NOM
NOM
NOM
R
R
= 0.536 and r
HOT
NTC HOT
NTC COLD
=
=
+ R
+ R
r
0.536
NOM
3.25
and r
r
COLD
= 0.536 • R
NTC HOT
NTC COLD
HOT
= 3.25 • R
equal to R25, the above equations result
COLD
• R25
• R25
COLD
• NTCBIAS = 0.349 • NTCBIAS
• NTCBIAS = 0.765 • NTCBIAS
are the resistance ratios at the de-
NOM
NOM
= 3.25. Referencing these ratios
NOM
, different in value from
NTC|COLD
and R
NTC|HOT
From the Vishay Curve 1 R-T characteristics, r
0.2488 at 60°C. Using the above equation, R
be set to 46.4k. With this value of R
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
as shown in Figure 10. The following formulas can be used
to compute the values of R
For example, to set the trip points to 0°C and 45°C with
a Vishay Curve 1 thermistor choose:
the nearest 1% value is 105k:
the nearest 1% value is 12.7k. The fi nal solution is shown
in Figure 10 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
Hot Plugging and USB Inrush Current Limiting
The overvoltage protection circuit provides inrush current
limiting due to the long time it takes for OVGATE to fully
enhance the N-channel MOSFET. This prevents the current
from building up in the cable too quickly thus dampen-
ing out any resonant overshoot on V
observe voltage overshoot on V
LTC3576/LTC3576-1 to a lab power supply if the overvoltage
protection circuit is not used. This overshoot is caused by
the inductance of the long leads from the power supply to
V
can greatly reduce the parasitic inductance of these long
leads keeping the voltage at V
are generally manufactured with the power leads in close
proximity, and thus have fairly low parasitic inductance.
BUS
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
R
R1= 0.536 • R
R
NOM
NOM
. Twisting the wires together from the supply to V
=
=
r
3.266 – 0.4368
COLD
2.714
2.714
NOM
– r
HOT
– r
HOT
• R25
NOM
• 100k = 104.2k
BUS
• R25
BUS
and R1:
to safe levels. USB cables
when connecting the
NOM
BUS
. It is possible to
, r
COLD
NOM
is 1.436
should
HOT
3576fb
BUS
is