LTC1644CGN#TR Linear Technology, LTC1644CGN#TR Datasheet - Page 16

• Manufacturer Part Number: LTC1644CGN#TR
• Description: IC CONTROLLER HOT SWAP 20-SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC1644CGN#TR

• Applications: CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V, ±12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP (0.154", 3.91mm Width)
• Family Name: LTC1644
• Package Type: SSOP N
• Operating Supply Voltage (min): 2.75/10.8/-10.8V
• Operating Supply Voltage (max): 13.2/-14V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 3.99mm
• Product Height (mm): 1.5mm
• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC1644CGNTR

APPLICATIO S I FOR ATIO
LTC1644
Calculating R
An equivalent circuit for one of the LTC1644’s circuit
breakers useful in calculating the value of the sense
resistor is shown in Figure 7. To determine the most
appropriate value for the sense resistor first requires the
maximum current required by the load under worst-case
conditions.
Two other parameters affect the value of the sense resis-
tor. First is the tolerance of the LTC1644’s circuit breaker
threshold. The LTC1644’s nominal circuit breaker thresh-
old is V
tolerance over process and temperature. Second is the
tolerance (RTOL) in the sense resistor. Sense resistors are
available in RTOLs of 1%, 2% and 5% and exhibit
temperature coefficients of resistance (TCRs) between
changes as a function of temperature depends on the I
power being dissipated by it. The power rating of the sense
resistor should accommodate steady-state fault current
levels so that the component is not damaged before the
circuit breaker trips.
The first step in calculating the value of R
I
threshold, V
case is expressed by Equation 6:
16
LOAD(MAX)
75ppm/ C and 100ppm/ C. How the sense resistor
5V
R
IN
SENSE
I
LOAD(MAX)
CB(NOM)
V
and the lower limit for the circuit breaker
CB(MIN)
CB
5V
Figure 7. Circuit Breaker Equivalent
Circuit for Calculating R
I
13
LOAD MAX
SENSE
IN
V
+
–
CB MIN
R
= 55mV; however, it exhibits 15mV
SENSE
(
(
. The maximum value for R
U
)
14
5V
)
SENSE
LTC1644*
*ADDITIONAL DETAILS OMITTED FOR CLARITY
V
V
V
CB(MAX)
CB(NOM)
CB(MIN)
U
= 40mV
= 70mV
= 55mV
SENSE
W
SENSE
SENSE
is based on
U
in this
1644 F07
(6)
2
R
The second step is to determine the nominal value of
the sense resistor which is dependent on its tolerance
(RTOL = 1%, 2%, or 5%) and standard sense resistor
values. Equation 7 can be used to calculate the nominal
value from the maximum value found by Equation 6:
Often, the result of Equation 7 may not yield a standard
sense resistor value. In this case, two sense resistors with
the same RTOL can be connected in parallel to yield
R
The last step requires calculating a new value for I
(I
(R
threshold, V
given by Equation 8:
Table 4 lists I
gested values of R
part numbers for these resistor values.
Table 4. I
where R
SENSE(NOM)
TRIP(MAX,NEW)
SENSE(MIN)
R
R
I
TRIP MAX NEW
SENSE
SENSE N M
0.005
0.007
0.011
0.028
0.055
(
TRIP
(1% RTOL)
SENSE MIN
(
0
vs R
CB(MAX)
,
.
) and the upper limit for the circuit breaker
TRIP(MIN)
(
)
) based on a minimum value for R
SENSE
)
SENSE
R
)
1
. The new value for I
SENSE MAX
R
Table
V
SENSE MIN
R
and I
CB MAX
RTOL
SENSE NOM
. Table 8 lists manufacturers and
100
I
TRIP(MIN)
(
(
7.92A
5.66A
3.60A
1.41A
0.72A
(
TRIP(MAX)
(
)
)
)
)
versus some sug-
1
TRIP(MAX,NEW)
I
RTOL
TRIP(MAX)
14.14A
10.10A
100
6.43A
2.53A
1.29A
TRIP(MAX)
SENSE
1644f
(7)
(8)
is