HV300LG-G データシートの表示（PDF） - Supertex Inc
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HV300LG-G Datasheet PDF : 7 Pages
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HV300
Functional Description
Insertion Into Hot Backplanes
Telecom, Data Network and some computer applications
require the ability to insert and remove circuit cards from
systems without powering down the entire system. All cir-
cuit cards have some filter capacitance on the power rails,
which is especially true in circuit cards or network terminal
equipment utilizing distributed power systems. The insertion
can result in high inrush currents that can cause damage to
connector and circuit cards and may result in unacceptable
disturbances on the system backplane power rails.
The HV300 was designed to allow the insertion of these
circuit cards or connection of terminal equipment by elimi-
nating these inrush currents and powering up these circuits
in a controlled manner after full connector insertion has been
achieved. The HV300 is intended to provide this function on
a negative supply rail in the range of -10 to -90V.
Operation
On initial power application an internal regulator seeks to
provide 10V for the internal IC circuitry. Until the proper
internal voltage is achieved all circuits are held reset, the
open drain PWRGD signal is inactive to inhibit the start of
any load circuitry and the gate to source voltage of the ex-
ternal N-channel MOSFET is held low. Once the internal un-
der voltage lock out (UVLO) has been satisfied, the circuit
checks the input supply voltage under voltage (UV) and over
voltage (OV) sense circuits to ensure that the input voltage
is within acceptable programmed limits. These limits are de-
termined by the selected values of resistors R1, R2 and R3,
which form a voltage divider.
Assuming the above conditions are satisfied and while con-
tinuing to hold the PWRGD output inactive and the external
MOSFET GATE voltage low, the current source feeding the
RAMP pin is turned on. The external capacitor connected to
it begins to charge, thus starting an initial time delay deter-
mined by the value of the capacitor. If an interruption of the
input power occurs during this time (i.e. caused by contact
bounce) or the OV or UV limits are exceeded, an immedi-
ate reset occurs and the external capacitor connected to the
RAMP pin is discharged.
When the voltage on the RAMP pin reaches an internally
set voltage limit, the gate drive circuitry begins to turn on the
external MOSFET; allowing the current to softly rise over a
period of a few hundred micro-seconds to the current limit
set point. While the circuit is limiting current, the voltage on
the RAMP pin will be fixed.
Depending on the value of the load capacitance and the
programmed current limit, charging may continue for some
time. The magnitude of the current limit is programmed by
comparing a voltage developed by a sense resistor connect-
ed between the VEE and SENSE pins to 50mV (Typical).
Once the load capacitor has been charged, the current will
drop which will cause the ramp voltage to continue rising;
providing yet another programmed delay.
When the ramp voltage is within 1.2V of the internally regu-
lated voltage, the controller will force the GATE full on and
will activate the PWRGD pin and the circuit will transition to a
low power standby mode. The PWRGD pin is often used as
an enable for downstream DC/DC converter loads.
At any time during the start up cycle or thereafter, crossing
the UV and OV limits (including hysteresis) will cause an im-
mediate reset of all internal circuitry. Thereafter the start up
process will begin again.
Application Information
Under Voltage and Over Voltage Detection
The UV and OV pins are connected to comparators with
nominal 1.21V thresholds and 100mV of hysteresis (1.21V
± 50mV). They are used to detect under voltage and over
voltage conditions at the input to the circuit. Whenever the
OV pin rises above its threshold or the UV pin falls below its
threshold the GATE voltage is immediately pulled low, the
PWRGD signal is deactivated and the external capacitor
connected to the RAMP pin is discharged.
The under voltage and over voltage trip points can be pro-
grammed by means of the three resistor divider formed by
R1, R2 and R3. Since the input currents on the UV and OV
pins are negligible the resistor values may be calculated as
follows:
UVOFF = VUVH = 1.16 = |VEEUV| • (R2+R3) / (R1+R2+R3)
OVOFF = VOVL = 1.26 = |VEEOV| • R3 / (R1+R2+R3)
Where |VEEUV| and |VEEOV| are Under & Over Voltage Set
points.
If we select a divider current of 100µA at a nominal operating
input voltage of 50V then:
(R1+R2+R3) = 50V / 100µA = 500kΩ
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
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