HV311LG Supertex, HV311LG Datasheet - Page 5

• Manufacturer Part Number: HV311LG
• Description: Hot Swap & Power Distribution Active Low
• Manufacturer: Supertex

Specifications of HV311LG

• Package Type: SOIC N
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 3.9mm
• Product Length (mm): 4.9mm
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8
• Lead Free Status / RoHS Status: Not Compliant

Functional Description
Once external power supply capacitors are charged, the
power supply current subsides, and the RAMP current in-
creases again to its maximum value of 10μA. The RAMP
and GATE voltages resume their rise. When the RAMP volt-
age is within 1.2V of the internal supply, then GATE is con-
nected to the internal supply, and the open-drain PWRGD
pin is released, marking the end of the start-up.
If the start-up sequence is not finished within 100ms, then
the internal start-up timer causes a reset of the RAMP and
GATE voltage to 0V, and the automatic retry timer is started
to allow the MOSFET to cool off. After the retry delay a new
startup sequence is initiated if the power supply voltage is
within the normal operating range, as determined by the UV
and OV comparators.
Design Information
Setting up the UV and OV comparators
The following example shows how the resistors for the
threshold setting divider can be determined. The procedure
applies to the (R1, R2, R3) divider having two taps as shown
on the typical applications diagram.
The following procedure bases the selection of the divider
resistors on specification of the shutdown / disable voltages.
A similar procedure can be devised that bases selection on
specification of the enable voltages.
Let’s assume the following:
The following applies:
R
3
•
•
•
•
•
•
•
•
•
•
•
•
•
•
follows from the OV shutdown voltage:
nominal divider current draw I
nominal power supply voltage V
overvoltage shutdown voltage V
undervoltage shutdown voltage V
negligible (UV, OV) comparator input currents,
Comparator rising threshold V
Comparator falling threshold V
R
R
R
DF
V
R
R
123
123
123
RTH
3
3
= R
= 9.692kΩ (97.6k 1%)
OV
= (R
= V
= 500kΩ
= V
= R
123
NOM
OVS
1
3
· V
+ R
/ R
/ I
· DF
RTH
123
NOM
2
+ R
/ V
OV
OVS
3
)
●
(cont.)
NOM
RTH
FTH
1235 Bordeaux Drive, Sunnyvale, CA 94089
NOM
OVS
= 100μA,
= 1.26V
UVS
= 1.16V
= 65V,
= 50V,
= 35V,
5
The circuit breaker monitors the sense amplifier for the pres-
ence of an overcurrent condition at all times. The overcur-
rent threshold is set at twice the maximum inrush current
threshold. Should overcurrent occur, then RAMP, GATE, and
PWRGD are brought to zero, and the automatic retry timer
is started.
The automatic retry timer can be disabled by attachment of
an additional resistor at the RAMP pin if a latched shutdown
is desired.
A further reduction in the ramp rate of the RAMP and GATE
voltages can be attained by connection of a feedback ca-
pacitor from the drain node to the RAMP pin. During startup
the drain voltage drops at a rate proportional to the inrush
current. This falling voltage waveform can be used to fur-
ther reduce the current that flows onto the RAMP capacitor,
thereby reducing the maximum inrush current.
R
And:
Now the upper and lower enable voltages can be deter-
mined:
Programming Maximum Inrush Current and Circuit
Breaker Current
The values of the current limit threshold voltage V
external current sense resistor R
power supply current during startup I
rush current). Similarly the circuit breaker trip current I
determined by the values of the circuit breaker threshold
voltage V
2
•
•
•
•
•
•
•
•
•
•
•
follows from the UV shutdown voltage:
DF
V
R
R2 = 6.879kΩ (6.81k 1%)
R1 = 483.429kΩ (487k 1%)
Lower Enable Voltage V
Upper Enable Voltage V
V
V
V
V
FTH
RTH
FTH
LEN
UEN
2
UV
+ R
CB
= V
= DF
= 38.0V
●
= DF
= 59.8V
= (R
and the value of R
3
Tel: [phone]
= R
UVS
OV
2
UV
+ R
· DF
123
· V
· V
· V
3
LEN
UEN
) / R
UV
FTH
123
/ V
●
UVS
LEN
UEN
CS
www.supertex.com
.
CS
determine the maximum
MAX
(the maximum in-
HV301
CL
and the
CB
is