Ramp - Linear Technology DC116 Series Demo Manual

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
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.
• Connect the negative power supply to V
and GND (TP6) on DC116B. Do not exceed –12.6V
on V .
EE
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 0.005Ω sense resistor (R1) sets the current limit to 10A
at the V output; R3 (0.025Ω) sets the current limit at V
CC
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 • dV
OUT OUT
power supply can then be limited to a safe value. The ramp
slope is determined by a fixed internal current source
(20µA) and a ramp capacitor (C9) connected between the
RAMP and GATEHI pins. The voltage at GATEHI rises with
6
Arrow.com. Arrow.com. Arrow.com. Arrow.com. Arrow.com. Arrow.com.
Downloaded from Downloaded from Downloaded from Downloaded from Downloaded from Downloaded from
(TP9) and the higher one to V
CC
U
, V and V , to be safely inserted
DD CC EE
CC
is a negative supply.
EE
CC
. The nominal
DD
, 12V for V and –12V for V
CC DD
/dt) drawn from the main backplane
• Connect the loads to outputs V
and V
EE2
return side of the lead(s) to TP12 or TP16 (GND).
• Select the proper dip switches to monitor the outputs
(TP8) and set the trip level for the RESET output.
DD
• Apply power and insert the daughter board (DC116A)
into the system backplane (DC116B). Rock the daugh-
ter board back and forth to ensure good connection.
(TP7)
EE
• The LEDs will turn on to indicate the status of the input
and output supplies as well as the circuit breaker.
a slope equal to 20µA/C
pin is clamped one Schottky diode drop below GATEHI.
and V are
DD
The negative supply voltage can be controlled using the
CPON pin. When the board makes a connection, the
; its voltage
N-channel pass transistor, Q2, is turned off by R4. CPON
is also pulled down to V
.
EE
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
DD
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.
(TP8), V
CC2
(TP2) on the DC116A board. Connect the
. The voltage at the GATELO

RAMP

. When the charge pump is
EE1
and the gate of Q2 ramps
CC1
and V . A number of similar
DD EE
(TP3)
DD2
EE1
output
CC
to
DS(ON)