LTC1647-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1647-1' PDF : 20 Pages View PDF
LTC1647-1/LTC1647-2/LTC1647-3
APPLICATIO S I FOR ATIO
If a dead short occurs after a supply connection is made
(Figure 12), the sense resistor R1 and the RDS(ON) of fully
enhanced Q1 provide a low impedance path for nearly
unlimited current flow. The LTC1647 discharges the GATE
pin in a few microseconds, but during this discharge time
current on the order of 150 amperes flows from the VCC
power supply. This current spike glitches the power sup-
ply, causing VCC to dip (Figure 12a and 12b).
On recovery from overload, some supplies may over-
shoot. Other devices attached to this supply may reset or
malfunction and the overshoot may also damage some
components. An inductor (1µH to 10µH) in series with
Q1’s source limits the short-circuit di/dt, thereby limiting
the peak current and the supply glitch (Figure 12c and
12d). Additional power supply bypass capacitance also
reduces the magnitude of the VCC glitch.
VID Power Controller
The two Hot Swap channels of the LTC1647 are ideally
suited for VID power control in portable computers.
Figure 13 shows an application using the LTC1647-2 on
the system side of the device bay interface (1394 PHY and/
or USB). The controller detects the presence of a periph-
eral in each device bay and controls the LTC1647-2. The
timing waveform illustrates the following sequence of
events: t1, rising out of undervoltage lockout with GATE 1
ramping up; t2, load current fault at R1; t3, circuit breaker
resets with R5/C3 delay; t4/t5, controller gates off/on
device supply with RC delay; t6, device enters undervolt-
age lockout.
If C6 is not connected in Figure 13, FAULT 2 and ON2 will
have similar waveforms. t7 initiates an ON sequence; t8, a
load fault is detected at R7 with FAULT 2 pulling low. If the
controller wants to stretch the interval between retries, it
can pull ON2 low at t9 ( t9 – t8 < 0.4•tRESET). At t10/t11, the
controller initiates a new power-up/down sequence.
13
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