ltc3566 Linear Technology Corporation, ltc3566 Datasheet - Page 23

• Manufacturer Part Number: ltc3566
• Description: High Ef?ciency Usb Power Manager Plus 1a Buck-boost Converter
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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.
From the Vishay Curve 1 R-T characteristics, r
at 60°C. Using the above equation, R
to 46.4k. With this value of R
about 16°C. Notice that the span is now 44°C rather than
the previous 40°C. This is due to the decrease in “tem-
perature gain” of the thermistor as absolute temperature
increases.
The upper and lower temperature trip points can be in-
dependently programmed by using an additional bias
resistor as shown in Figure 4b. 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:
R1 = 0.536 • R
R
NOM
V
BUS
R
100k
HOT
NOM
NTC
R
100k
=
1
NTC
r
and r
COLD
2.714
V
BUS
COLD
− r
0.17 • V
NOM
0.349 • V
0.765 • V
HOT
are the resistance ratios at the de-
– r
BUS
BUS
BUS
• R25
HOT
• R25
–
+
–
+
+
–
NOM
NTC BLOCK
LTC3566
(a)
, the cold trip point is
NOM
NOM
should be set
TOO_COLD
TOO_HOT
NTC_ENABLE
HOT
and R1:
is 0.2488
Figure 4. NTC Circuits
3566 F04a
The nearest 1% value is 105k
The nearest 1% value is 12.7k. The fi nal solution is shown
in Figure 4b and results in an upper trip point of 45°C and
a lower trip point of 0°C.
USB Inrush Limiting
When a USB cable is plugged into a portable product,
the inductance of the cable and the high-Q ceramic input
capacitor form an L-C resonant circuit. If the cable does
not have adequate mutual coupling or if there is not much
impedance in the cable, it is possible for the voltage at
the input of the product to reach as high as twice the USB
voltage (~10V) before it settles out. To prevent excessive
voltage from damaging the LTC3566 during a hot insertion,
it is best to have a low voltage coeffi cient capacitor at the
V
MLCC capacitor that has a higher voltage rating than that
required for the application. For example, a 16V, X5R, 10μF
capacitor in a 1206 case would be a more conservative
choice than a 6.3V, X5R, 10μF capacitor in a smaller 0805
BUS
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
R
V
NOM
BUS
pin to the LTC3566. This is achievable by selecting an
R
105k
R1
12.7k
NOM
NTC
R
100k
=
1
NTC
3.266 − 0.4368
V
2.714
BUS
0.17 • V
0.349 • V
0.765 • V
BUS
BUS
BUS
• 100k = 104.2k
–
+
–
+
+
–
NTC BLOCK
LTC3566
(b)
LTC3566
TOO_COLD
TOO_HOT
NTC_ENABLE
23
3566 F04b
3566p