LTC1647-2CS8#TR Linear Technology, LTC1647-2CS8#TR Datasheet - Page 11

• Manufacturer Part Number: LTC1647-2CS8#TR
• Description: IC CONTROLLER HOTSWAP DUAL 8SOIC
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC1647-2CS8#TR

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 2.7 V ~ 16.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
FAULT
V
V
CC
CC
V
V
CC
CC
V
– V
CC
ON
R3
10k
Figure 3. Filtering Current Ripple/Glitches
V
V
SENSE
FAULT
0.01Ω
10nF
GATE
*D1, D4 USER SELECTED VOLTAGE CLAMP
1N4688 (5V)
1N4692 (7V): LOGIC-LEVEL MOSFET
1N4695 (9V)
1N4702 (15V): STANDARD-LEVEL MOSFET
**D5 DDZ23 (23V) REQUIRED FOR V
V
R1
C3
ON
2
3
8
Figure 1. Supply Control Circuitry
LTC1647
Figure 2. Current Fault Timing
SENSE
Figure 4. Optional Gate Clamp
D1*
ON1
FAULT
GND
*D1 REQUIRED FOR V
V
CC
R1
R3
1.5k
1
1N4148
0.01Ω
R1
D2
IRF7413
LTC1647-3
GATE
Q1
SENSE
R2
10Ω
15
Q1
+
**D5
CC
IRF7413
1N4148
GATE
Q1
> 10V
D2
t
C1
10nF
C
13
FAULT
t
R2
10Ω
RESET
LOAD
V
OUT
CC
> 10V
D4*
I
I
I
t
PK
AV
TRIP
DELAY
+
C1
10nF
= 7.5A
= 2.5A
1647-1/2/3 F04
= V
1647-1/2/3 F02
= 10μs
C
CB
V
LOAD
V
OUT
1647-1/2/3 F03
/R1 = 5A
OUT
1647-1/2/3 F01
*D1
DDZ23
where V
I
breaker trips. Kelvin-sense layout techniques between
the sense resistor and the V
recommended for proper operation.
The circuit breaker trip voltage has a tolerance of 20%;
combined with a 5% sense resistor, the total tolerance is
25%. Therefore, calculate R1 based on a trip current I
of no less than 125% of the maximum operating current.
Do not neglect the effect of ripple current, which adds to
the maximum DC component of the load current. Ripple
current may arise from any of several sources, but the
worst offenders are switching supplies.
A switching regulator on the load side will attempt to draw
some ripple current from the backplane and this current
passes through the sense resistor. Similarly, output ripple
from a switching regulator supplying the backplane will flow
through the sense resistor and into the load capacitor.
Minimize the effects of ripple current by either filtering the
V
inductance of 1μH to 10μH inserted between Q1 and C
is adequate ripple current suppression in most cases.
Alternatively, a filter, consisting of R3 and C3 (Figure 3),
simply filters the ripple component from the SENSE pin at the
expense of response time. The added delay is given by:
Power MOSFET Selection
Power MOSFETs are classified into two catagories: standard
MOSFETs (R
MOSFETs (R
maximum rating for V
MOSFETs. The maximum rating for logic-level MOSFETs
is lower and ranges from 8V to 16V depending on the
manufacturer and specific part number. Some logic-level
MOSFETs have a 20V maximum V
is primarily targeted for standard MOSFETs; low supply
voltage applications should use logic-level MOSFETs. GATE
overdrive as a function of V
Performance Curves. If lower GATE overdrive is desired,
connect a diode in series with a Zener between GATE and
V
TRIP
OUT
CC
t
DELAY
or between GATE and V
is the value of the load current at which the circuit
line or adding an RC filter to the SENSE pin. A series
CB
= – R3•C3•ln[1 – (V
is the circuit breaker trip voltage (50mV) and
LTC1647-2/LTC1647-3
DS(ON)
DS(ON)
specified at V
specified at V
GS
is typically 20V for standard
CC
CC
OUT
CB
and SENSE pins are highly
is illustrated in the Typical
/R1 – I
as shown in Figure 4. For
GS
LTC1647-1/
GS
GS
= 10V) and logic-level
rating. The LTC1647
= 5V). The absolute
AV
)/(I
PK
– I
AV
11
)]
LOAD
1647fa
TRIP