LTC1646CGN Linear Technology, LTC1646CGN Datasheet - Page 13

• Manufacturer Part Number: LTC1646CGN
• Description: IC CNTRLR HOTSWAP PCIDUAL 16SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC1646CGN

• Applications: CompactPCI™
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 5V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
5V
the 3.3V supply, a sense resistor is connected between
3V
current foldback current level are given by Equations 4
and 5:
where XV
As a design aid, the current limit and foldback level for
commonly used values for R
Table 3. I
R
0.005
0.006
0.007
0.008
0.009
0.01
where XV
SENSE
5V
IN
IN
I
I
LIMIT XVOUT
FOLDBACK XVOUT
IN
100mV/DIV
(Pin 12) and 5V
(Pin 8) and 3V
–5V
(Ω)
10V/DIV
5V/DIV
FAULT
SENSE
LIMIT(XVOUT)
(
GATE
OUT
OUT
(
Figure 6. Short-Circuit Fault on 5V
= 3V
= 5V
)
=
OUT
OUT
and I
SENSE
R
U
I
)
LIMIT(XVOUT)
SENSE
SENSE XVOUT
=
9.2A
7.9A
6.9A
6.1A
5.5A
or 5V
or 3V
11A
FOLDBACK(XVOUT)
R
55
(Pin 9). The current limit and the
SENSE XVOUT
U
mV
(Pin 11) for the 5V supply. For
(
OUT
20
OUT
SENSE
mV
(
5µs/DIV
.
.
)
W
is shown in Table 3.
vs R
)
I
FOLDBACK(XVOUT)
SENSE
3.3A
2.9A
2.5A
2.2A
4A
2A
U
1646 F06
(4)
(5)
Calculating R
An equivalent circuit for one of the LTC1646’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 LTC1646’s circuit breaker
threshold. The LTC1646’s nominal circuit breaker
threshold is V
–6mV/+9mV tolerance due to process variations. 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 ±75ppm/°C and ±100ppm/°C. How the sense
resistor changes as a function of temperature depends on
the I
The first step in calculating the value of R
I
threshold, V
case is expressed by Equation 6:
The second step is to determine the nominal value of the
sense resistor which is dependent on its tolerance
TRIP(MAX)
R
2
SENSE MAX
R power being dissipated by it.
5V
(
Figure 7. Circuit Breaker Equivalent
Circuit for Calculating R
IN
and the lower limit for the circuit breaker
CB(MIN)
I
LOAD(MAX)
SENSE
CB(NOM)
)
=
5V
I
12
. The maximum value for R
TRIP MAX
IN
V
3
1
–
+
–
CB MIN
R
SENSE
(
V
(
= 56mV; however, it exhibits a
CB
+
2
)
4
11
5V
)
LTC1646*
SENSE
SENSE
V
V
V
*ADDITIONAL DETAILS
OMITTED FOR CLARITY
CB(MAX)
CB(NOM)
CB(MIN)
LTC1646
SENSE
= 50mV
= 65mV
= 56mV
SENSE
is based on
1646 F07
13
in this
1646fa
(6)