DC116A-B Linear Technology, DC116A-B Datasheet - Page 6

• Manufacturer Part Number: DC116A-B
• Description: LTC1421 Evaluation Kit
• Manufacturer: Linear Technology

OPERATIO
The circuit shown in the Schematic Diagram allows three
power supplies, V
into and removed from the backplane. V
both positive supplies, whereas V
The main supply to the LTC1421 is from V
should be less than or equal to that of V
voltages are 5V for V
A 0.005 sense resistor (R1) sets the current limit to 10A
at the V
to 2A. The LTC1421 monitors the voltage across the sense
resistors. When either voltage is greater than 50mV, the
internal charge pump is turned off immediately and both
the gates and voltage outputs are actively pulled to ground.
The circuit breaker function remains active until the push-
button switch (S2) is pressed and released or the power is
cycled.
The LTC1421 limits the inrush current through the
N-channel pass transistor by increasing the voltage on the
gate in a controlled manner. The transient surge current
(I = C
power supply can then be limited to a safe value. The ramp
slope is determined by a fixed internal current source
(20 A) and a ramp capacitor (C9) connected between the
RAMP and GATEHI pins. The voltage at GATEHI rises with
6
DEMO MANUAL DC116
HOT SWAP CONTROLLER
QUICK START GUIDE
The demonstration board set, DC116, is easily set up for
evaluation of the LTC1421 IC. Please follow the proce-
dure outlined below for error-free operation.
• Connect the positive power supply with the lower
• Connect the negative power supply to V
potential to V
on DC116B. Connect the ground lead(s) to TP6. Do
not exceed 12.6V for either supply to ensure proper
operation of the LTC1421.
and GND (TP6) on DC116B. Do not exceed –12.6V
on V
OUT
CC
EE
output; R3 (0.025 ) sets the current limit at V
• dV
.
OUT
CC
U
DD
/dt) drawn from the main backplane
(TP9) and the higher one to V
, V
CC
, 12V for V
CC
and V
EE
EE
DD
, to be safely inserted
is a negative supply.
and –12V for V
DD
CC
CC
. The nominal
and V
; its voltage
EE
DD
DD
(TP8)
(TP7)
EE
are
DD
.
a slope equal to 20 A/C
pin is clamped one Schottky diode drop below GATEHI.
The negative supply voltage can be controlled using the
CPON pin. When the board makes a connection, the
N-channel pass transistor, Q2, is turned off by R4. CPON
is also pulled down to V
turned on, CPON is pulled to V
up with a time constant determined by R4, R5 and C2.
When the charge pump is turned off, CPON goes into high
impedance state; the gate of Q2 is then discharged to V
with a time constant determined by R4 and C2 and then Q2
turns off. There is no circuit breaker or current-limit
feature on the negative supply.
Power N-Channel MOSFET
External N-channel pass transistors are used to route the
power from the system power supply to the plug-in board.
An MTB50N06E from Motorola is used for the V
and two 8-lead, surface mounted NFETs from Siliconix
(Si4410DY) are used for V
N-channel MOSFETs, available from different manufactur-
ers, are also well-suited for this type of application. As a
general rule, select the MOSFET with the lowest R
get the smallest voltage drop across it at the maximum
output load.
• Connect the loads to outputs V
• Select the proper dip switches to monitor the outputs
• Apply power and insert the daughter board (DC116A)
• The LEDs will turn on to indicate the status of the input
and V
return side of the lead(s) to TP12 or TP16 (GND).
and set the trip level for the RESET output.
into the system backplane (DC116B). Rock the daugh-
ter board back and forth to ensure good connection.
and output supplies as well as the circuit breaker.
EE2
(TP2) on the DC116A board. Connect the
RAMP
EE1
DD
. When the charge pump is
and V
. The voltage at the GATELO
CC1
and the gate of Q2 ramps
CC2
EE
. A number of similar
(TP8), V
DD2
CC
DS(ON)
(TP3)
output
EE1
to