LTC4251 LINER [Linear Technology], LTC4251 Datasheet - Page 8

• Manufacturer Part Number: LTC4251
• Description: Negative Voltage Hot Swap Controllers in SOT-23
• Manufacturer: LINER [Linear Technology]

OPERATIO
LTC4251/LTC4251-1/
LTC4251-2
BLOCK DIAGRA
pin of the LTC4251-2. Secondly, all overvoltage conditions and references to OV, V
the OV comparator in this part is disabled.
Hot Circuit Insertion
When circuit boards are inserted into a live backplane, the
supply bypass capacitors can draw huge transient currents
from the power bus as they charge. The flow of current
damages the connector pins and glitches the power bus,
causing other boards in the system to reset. The LTC4251/
LTC4251-1/LTC4251-2 are designed to turn on a circuit
board supply in a controlled manner, allowing insertion or
removal without glitches or connector damage.
Initial Start-Up
The LTC4251/LTC4251-1/LTC4251-2 reside on a remov-
able circuit board and control the path between the con-
nector and load or power conversion circuitry with an
8
UV/OV*
TIMER
V
IN
3
5
4
*UV FOR THE LTC4251-2
** THE OV COMPARATOR IS DISABLED FOR LTC4251-2
230µA
V
EE
V
U
V
EE
IN
5.8µA
5.8µA
Note that for simplicity, the following assumptions are made in the text. Firstly, UV/OV also means the UV
V
V
W
EE
IN
V
V
UVLO
OVHI
4V
1V
–
+
–
+
–
+
–
+
OV**
UV
LOGIC
V
2
EE
CB
external MOSFET switch (see Figure 1). Both inrush con-
trol and short-circuit protection are provided by the
MOSFET.
A detailed schematic is shown in Figure 2. –48V and
–48RTN receive power through the longest connector
pins, and are the first to connect when the board is
inserted. The GATE pin holds the MOSFET off during this
time. UV/OV determines whether or not the MOSFET
should be turned on based upon internal, high-accuracy
thresholds and an external divider. UV/OV does double
duty by also monitoring whether or not the connector is
seated. The top of the divider detects –48RTN by way of a
short connector pin that is the last to mate during the
insertion sequence.
+
–
V
V
V
V
IN
EE
EE
IN
5k
58µA
22µA
V
OVHI
50mV
OS
+ –
= 10mV
–
and V
+
V
EE
OVLO
+
–
FCL
ACL
+
+
–
–
do not apply to the LTC4251-2 as
200mV
+ –
0.5V
V
EE
V
EE
425112 BD
6
1
GATE
SENSE
425112fa