LTC1646CGN Linear Technology, LTC1646CGN Datasheet - Page 14

• 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
LTC1646
(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
R
breaker threshold, V
for I
for I
selected and the process repeated. The new value for
I
Example : A 5V supply exhibits a nominal 5A load with a
maximum load current of 6.8A (I
sense resistors with ±5% RTOL will be used. According to
Equation 6, V
The nominal sense resistor value is (Equation 7):
And the new current-limit trip point is Equation 8:
14
TRIP(MAX)
TRIP(MAX, NEW)
SENSE(NOM)
SENSE
I
where R
R
TRIP MAX NEW
R
R
TRIP(MAX, NEW)
SENSE NOM
TRIP(MAX)
SENSE MAX
SENSE NOM
(
(R
(I
(
(
(
SENSE(MIN)
SENSE MIN
TRIP(MAX, NEW)
,
.
CB(MIN)
, a larger sense resistor value should be
)
)
)
is given by Equation 8:
)
=
=
(
=
=
be much greater than the design value
I
R
R
U
1
1
TRIP MAX
V
R
CB(MAX)
SENSE MAX
= 50mV and R
SENSE MAX
+
) and the upper limit for the circuit
+
)
CB MIN
V
SENSE MIN
=
⎛
⎜
⎝
⎛
⎜
⎝
CB MAX
(
(
RTOL
RTOL
R
100
100
(
U
) based on a minimum value for
SENSE NOM
(
(
(
)
. Should the calculated value
)
⎞
⎟
⎠
)
=
⎞
⎟
⎠
)
)
)
(
50
=
6 8
LOAD(MAX)
SENSE(MAX)
.
W
mV
1
0 0074
A
+
)
.
• –
⎛
⎜
⎝
⎡
⎢
⎣
=
100
1
5
0 0074
Ω
.
⎛
⎜
⎝
⎞
⎟
⎠
= 6.8A), and
RTOL
is given by:
100
=
U
0 007
Ω
.
⎞
⎟
⎠
⎤
⎥
⎦
(7)
( )
Ω
8
Since I
R
to lower I
I
Output Voltage Monitor
The status of both 5V and 3.3V output voltages is moni-
tored by the power good function. In addition, the PCI_RST#
signal is logically combined on-chip with the HEALTHY#
signal to create LOCAL_PCI_RST# (see Table 4).
Table 4. LOCAL_PCI_RST# Truth Table
If either of the output voltages drop below the power good
threshold for more than 50µs, the HEALTHY# signal will be
pulled high and the LOCAL_PCI_RST# signal will be pulled
low.
Precharge
The PRECHARGE input and DRIVE output pins are in-
tended for use in generating the 1V precharge voltage that
is used to bias the bus I/O connector pins during board
insertion. The LTC1646 is also capable of generating
precharge voltages other than 1V. Figure 8 shows a circuit
that can be used in applications requiring a precharge
voltage less than 1V. The circuit in Figure 9 can be used for
applications that need precharge voltages greater than 1V.
Table 5 lists suggested resistor values for R1 and R2 vs
precharge voltage for the application circuits shown in
Figures 8 and 9.
LOAD(MAX)
SENSE
PCI_RST#
I
R
TRIP MAX NEW
SENSE N M
LO
LO
HI
HI
TRIP(MAX, NEW)
should be selected and the process repeated again
(
TRIP(MAX, NEW)
(
.
0
,
V
CB MAX
)
• –
(
)
⎡
⎢
⎣
=
1
HEALTHY#
R
)
⎛
⎜
⎝
V
SENSE MIN
LO
LO
HI
HI
> I
RTOL
CB MAX
100
without substantially affecting
(
LOAD(MAX)
(
⎞
⎟
⎠
)
⎤
⎥
⎦
)
=
=
0 0065
65
, a larger value for
.
mV
LOCAL_PCI_RST#
=
LO
LO
LO
HI
9 8
.
A
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