HV301 SUTEX [Supertex, Inc], HV301 Datasheet - Page 8

• Manufacturer Part Number: HV301
• Description: Hotswap, Controllers with Circuit Breaker
• Manufacturer: SUTEX [Supertex, Inc]

Design Information, cont’d.
These equations assume that the load is purely capacitive and
the following definitions apply.
These equations may be used to calculate the minimum value of
C
For maximum contact bounce duration protection choose a
value for t
If control of PWRGD active delay is the critical system param-
eter, then choose a value for t
equation:
C
C
RAMP
RAMP
RAMP
C
I
10µA, when the voltage drop on R
V
from 8.5V to 12V.
V
transistor and may be obtained from its datasheet.
V
required to obtain the limit current. It is dependent on the
pass transistor’s characteristics and may be obtained from
the transfer characteristics on the transistor datasheet.
g
and may be obtained from its datasheet.
R
I
resistor is 50mV.
RAMP
LIMIT
fs
INT
GS(th)
GS( limit )
RAMP
FB
for the most critical system performance characteristics.
is the transconductance of the external pass transistor
=
is the internal feedback resistor and is nominally 5kΩ.
=
is the internally regulated supply voltage and can range
is the load current when the voltage drop on the R
is the output current from the RAMP pin, nominally
V
is the external capacitor connected to the RAMP pin.
t
POR
is the gate threshold voltage of the external pass
2 4 .
POR
INT
is the external pass transistor gate-source voltage
t
PWRGD
and use the following equation:
+
−
×
V
V
I
GS th
GS
RAMP
( )
×
(
limit
I
RAMP
)
−
1 2
.
PWRGD
SENSE
and use the following
resistor is zero.
SENSE
8
Due to the 2.5µA max charge current a resistor which draws
more than 2.5µA below 8V will disable the autoretry. Try to
keep this resistor as big as possible, e.g. 2.5MΩ, for most
MOSFETs with max V
current source by only 4/2.5MΩ=1.6µA.
Start up Overload Protection
Start up must be achieved within a nominal 100ms as indicated
by the PWRGD pin transition to the active state or the circuit will
reset and an automatic restart will initiate. If there is an output
overload or short circuit during start up, the circuit will be in
current limit for the 100ms time limit (in servo mode). In feedback
capacitor mode the circuit breaker will shutdown the pass FET
before 100ms.
Circuit Breaker
The circuit breaker will trip in less than 5µs when the voltage on
the SENSE pin reaches a nominal 100mV. A resistor in series
with the SENSE pin and a capacitor connected between the
SENSE and V
rise on the SENSE pin, thus permitting a current overshoot and
delaying Circuit Breaker activation.
Automatic Restart
The automatic restart delay time is directly proportional to the
capacitance at the RAMP pin. Automatic restart sequence is
activated whenever the 100ms timeout is reached during start up
or the circuit breaker is tripped.
2.5µA
2.5µA
EE
pins may be added to delay the rate of voltage
C
ramp
t
of 4V this will vary the 10µA Ramp
Auto-retry can be approximated as a
555-timer with 2.5µA charge up and
charge down currents through 8V, to
a count of 256. Therefore,
T
AUTORETRY
e.g.
2 8 256
× ×
2.5 A
µ
=
2 8 256
× ×
2.5 A
×
Ion = 16.4s
HV301/HV311
µ
×
C
ramp