LTC4211IS8 Linear Technology, LTC4211IS8 Datasheet - Page 27

• Manufacturer Part Number: LTC4211IS8
• Description: IC CTRLR HOTSWAP CURR CTRL 8SOIC
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4211IS8

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 2.5 V ~ 16.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
To increase the RC delay, the user may either increase
C
actually limit the RC delay due to the reset sink-current
capability of the FAULT pin. Therefore, in order to increase
the RC delay, it is more effective to either increase R
or to put a bleed resistor in parallel with C
an example, increasing R
duty cycle to 0.8%.
HOT SWAPPING TWO SUPPLIES
Using two external pass transistors, the LTC4211 can
switch two supply voltages. In some cases, it is necessary
to bring up the dominant supply first during power-up but
ramp them down together during the power-down phase.
The circuit in Figure 20 shows how to program two
different delays for the pass transistors. The 5V supply is
powered up first. R1 and C3 are used to set the rise and fall
times on the 5V supply. Next, the 3.3V supply ramps up
V
AUTO
CC
– V
FILTER
TIMER
RESET
SENSE
GATE
V
or R
V
OUT
CC
AUTO
1
DUTY CYCLE =
. However, increasing C
ON/FAULT
U
t
OFF
t
OFF
AUTO
U
+ t
t
2
1
+ t
from 1M to 3.2M decreases
2
(t
FILTER
W
2
<< t
1
, t
AUTO
AUTO
2
V
AND t
FB
t
1
< V
to GND. As
U
> 2µF will
OFF
Figure 19. Autoretry Timing
REF
)
AUTO
3
4
FAST COMPARATOR ARMED
5
LOAD CURRENT
V
with 20ms delay set by R6 and C2. On the falling edge, both
supplies ramp down together because D1 and D2 bypass
R1 and R6.
OVERVOLTAGE TRANSIENT PROTECTION
Good engineering practice calls for bypassing the supply
rail of any analog circuit. Bypass capacitors are often
placed at the supply connection of every active device, in
addition to one or more large value bulk bypass capacitors
per supply rail. If power is connected abruptly, the large
bypass capacitors slow the rate of rise of the supply
voltage and heavily damp any parasitic resonance of lead
or PC track inductance working against the supply bypass
capacitors.
The opposite is true for LTC4211 Hot Swap circuits
mounted on plug-in cards. In most cases, there is no
supply bypass capacitor present on the powered supply
SENSE
REGULATED
6
t
2
= 50mV
GATE
V
OUT
SLOW COMPARATOR ARMED
7
8
t
FILTER
>50mV
V
2µA
REF
B
FPD
10µA
t
RESET
ON/FAULT
t
OFF
LTC4211
4211 F19
27
4211fa