HV302 Supertex Inc, HV302 Datasheet - Page 7

• Manufacturer Part Number: HV302
• Description: Sequencing Hotswap Controllers
• Manufacturer: Supertex Inc

Design Information-
Programming Current Limit and Circuit Breaker
Feedback Capacitor Mode Operation
In this operating mode the circuit breaker trip current and the
inrush current limit can be independently programmed. In fact the
circuit breaker can be completely disabled by setting R
The circuit breaker will trip in less than 5 s when the voltage on
the SENSE pin is raised 100mV above the V
the sense resistor may be calculated from the following equation:
For an 8A circuit breaker:
The power rating of the sense resistor must be greater than or
equal to I
The following diagrams depict the equivalent circuitry to clarify the
feedback capacitor operation for programming the inrush current
limit.
The inrush current limit may be programmed as follows:
Choose inrush current limit, for example I
Calculate
If the Circuit Breaker function is disabled by setting R
then I
Circuit Breaker function is enabled and therefore use I
SINK
CB
Supertex, Inc. 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: [phone] Fax: [phone] www.supertex.com
R
R
= 0A. However, in this example we assume that the
I
x V
SENSE
SENSE
SINK
SENSE-CB
I
CL
100mV
V
SENSE
8A
.
k 5
I
R
CB
SENSE
-
CB
12.5mΩ
100mV
1
continued
I
A
CB
k 5
12
5 .
CL
m
= 1A
EE
pin and the value of
2
5 .
A
SINK
SENSE
SENSE
= 2.5 A.
= 0 .
= 0 ,
7
Calculate C2 (feedback capacitor) discharge current
If Auto-Retry is disabled an adjustment must be made to I
Where Vt is the maximum threshold voltage of the MOSFET.
Therefore, the adjusted value of I
In this example we assume that Auto-Retry is enabled and
therefore use I
Note that
Since V
and their other terminals are at fixed voltages during inrush current
limiting. Therefore,
As previously calculated and by conservation of charge on RAMP
node I
Given that C
calculated.
Therefore
Note that during initial power application the RAMP pin is voltage
protected by the capacitive AC voltage divider consisting of C
C2 and C
Servo Control Mode Operation
The circuit breaker will trip in less than 5 s when the voltage on
the SENSE pin is raised 100mV above the V
the sense resistor may be calculated from the following equation:
For a 2A circuit breaker:
The power rating of the sense resistor must be greater than or
equal to I
dv
dt
across C
C2
IN
=7.5 A based on the chosen inrush current limit of I
CB
RAMP
is fixed and V
I
I
I
I
R
R
C
AUTO
C
C
x V
I
C
SENSE
SENSE
2
2
2
C
2
2
LOAD
and the GATE pin is internally clamped.
C2
LOAD
SENSE-CB
10
10
10
= 7.5 A.
C
I
R
C
=
=100 F the required value for C2 can be
2
2
A
A
A
100mV
DISABLE
V
Rev. D
I
C
V
SENSE
dv
C
I
dt
CL
2A
dv
2
C
.
t
2
dt
I
I
I
2
CB
RAMP
SINK
SINK
LOAD
5 .
across C2 as they share a common node
-
CB
C
A
I
is constant during limiting, then
LOAD
CL
2
and
I
10
AUTO
50mΩ
5 .
4
7
1
100mV
M
V
5 .
6 .
C2
A
I
or
CB
A
is:
A
I
1
CL
C
2
A
5 .
1
2
100
6 .
5
9 .
C
A
I
A
LOAD
C
HV302 / HV312
F
A
2
EE
7
I
5 .
CL
C
pin and the value of
. 0
LOAD
dv
dt
75
A
nF
.
04/17/02
C2
CL
=1A.
LOAD
,