LTC4088 LINER [Linear Technology], LTC4088 Datasheet - Page 19

• Manufacturer Part Number: LTC4088
• Description: High Effi ciency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

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 inde-
pendently 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:
the nearest 1% value is 105k:
APPLICATIO S I FOR ATIO
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
R
R
R
V
NOM
1 0 536
NOM
BUS
=
T
R
100k
NOM
NTC
R
100k
1
NTC
.
=
=
r
3 266 0 4368
COLD
.
•
2 714
V
R
BUS
.
2 714
NOM
0.349 • V
–
.
0.765 • V
– .
U
r
HOT
0.1V
–
BUS
BUS
r
HOT
•
R
U
(4a)
NOM
25
•
–
+
–
+
+
–
•
100
NTC BLOCK
NOM
R R 25
LTC4088
and R1:
k
, the cold trip point is
=
W
104 2
NOM
.
should be set
TOO_COLD
TOO_HOT
NTC_ENABLE
k
HOT
U
is 0.2488
Figure 4. NTC Circuits
4088 F04a
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
The USB specifi cation allows at most 10µF of downstream
capacitance to be hot-plugged into a USB hub. In most
LTC4088 applications, 10µF should be enough to provide
adequate fi ltering on V
the following circuit can be used to soft-connect additional
capacitance.
In this circuit, capacitor C1 holds MP1 off when the cable
is fi rst connected. Eventually the bottom plate of C1 dis-
charges to GND, applying increasing gate support to MP1.
V
BUS
5V USB
T
R
105k
R1
12.7k
INPUT
NOM
NTC
R
100k
1
NTC
USB CABLE
Figure 5. USB Soft-Connect Circuit
V
BUS
0.349 • V
0.765 • V
0.1V
BUS
BUS
BUS
. If more capacitance is required,
C1
100nF
(4b)
–
+
–
+
+
–
Si2333
NTC BLOCK
MP1
LTC4088
R1
40k
LTC4088
C2
V
GND
TOO_COLD
TOO_HOT
LTC4088
NTC_ENABLE
BUS
4088 F05
19
4088 F04b
4088f