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LTC4251B Datasheet(PDF) 18 Page - Linear Technology

Part No. LTC4251B
Description  Negative Voltage Hot Swap Controllers in SOT-23
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LTC4251B Datasheet(HTML) 18 Page - Linear Technology

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18
4251b12f
LTC4251B/LTC4251B-1/
LTC4251B-2
APPLICATIONS INFORMATION
Analog Current Limit and Fast Current Limit
In Figure 13a, when SENSE exceeds VACL,GATEisregulated
by the analog current limit amplifier loop. When SENSE
drops below VACL, GATE is allowed to pull up. In Figure
13b, when a severe fault occurs, SENSE exceeds VFCL
and GATE immediately pulls down until the analog current
amplifier can establish control. If TIMER reaches VTMRH,
GATE pulls low and latches off.
Resetting a Fault Latch
As shown in Figure 14, a latched fault is reset by either
pulling UV/OV below VUVLO or pulling TIMER below VTMRL.
An initial timing cycle is initiated if UV/OV is used for reset.
If TIMER is used for reset, the initial timing cycle is skipped.
Internal Soft-Start
An internal soft-start feature ramps the positive input of
the analog current limit amplifier during initial start-up.
The ramp duration is approximately 200μs. This feature
reduces load current dl/dt at start-up. As illustrated in
Figure 15, soft-start is initiated by a TIMER transition from
VTMRH to VTMRL or when UV/OV falls below the VOVLO
threshold after an OV fault. After soft-start duration, load
current is limited by VACL/RS.
Figure 9. Undervoltage Lockout Timing (All Waveforms are Referenced to VEE)
13
24
5 6
7 8 9
VUV/0V CLEARS VUVHI, CHECK TIMER < VTMRL, GATE < VGATEL AND SENSE < VCB.
VUV/0V DROPS BELOW VUVLO. TIMER, GATE, AND SENSE ARE PULLED TO VEE.
TIMER CLEARS VTMRL, CHECK GATE < VGATEL AND SENSE < VCB.
VUVHI
VUVLO
VTMRH
VTMRL
VACL
VCB
5.8μA
230μA
58μA
58μA
5.8μA
5.8μA
INITIAL TIMING CYCLE
START-UP CYCLE
4251b12 F09
UV/0V
TIMER
GATE
SENSE


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