HV312DB1
Schematic
V
IN+
14
Hotswap Controller
V
OUT+
V
DD
R
1
487k
R
2
9.09k
R
3
9.09k
6
UV
OV
V
EE
7
PWRGD
A
PWRGD
B
PWRGD
C
PWRGD
D
T
B
T
C
T
D
4
3
2
1
HV312
11
12
13
R
8
121k
C
5
not used
R
9
60.4k
5
RAMP
10
SENSE
8
GATE
9
R
10
3.01k
C
6
100*F
R
4
not used
C
1
10nF
C
2
not used
C
3
680pF
R
7
not used
R
6
0
V
IN-
R
5
15m
C
4
not used
Q
1
IRF3710S
V
OUT-
Inrush Limit
As supplied, the inrush current limit is set at 1 amp. To set
inrush limit to another value, please refer to the HV302/312
data sheet.
The circuit breaker trip point is set at 6.7 Amps. To set at a
different level, change R
5
according to the following
equation:
Circuit Breaker Transient Immunity
The HV312 has built-in transient immunity of 2–5*s. To
increase transient immunity, an RC low-pass filter (R
6
C
2
)
may be placed on the SENSE input. (The demo board is
supplied with no filtering.)
Be aware that filtering the sense input will cause the inrush
current limit to overshoot at turn-on – the greater the filtering,
the greater the overshoot.
I
CB
=
100mV
R
5
Undervoltage/Overvoltage Lockout
Resistors R
1
, R
2
, and R
3
set the undervoltage and
overvoltage trip points. New trip points may be programmed
by changing the values of these resistors. Refer to the
HV302/312 data sheet for more information.
The power rating of R
5
should be selected based on
maximum current during normal operation, which could be
just under the circuit breaker trip point.
P
5
=
100mV
I
CB
Additional Components
The RC network (R
7
C
4
) across the gate-source of the
external FET provides control loop compensation which
prevents inrush current peaking.
If the PWRGD A signal is used and experiences large
voltage swings, a 10nF capacitor should be installed at C
5
.
This limits dV/dt which may otherwise cause undesirable
coupling to internal circuits.
To defeat the circuit breaker auto-retry, install a 2.4M
resistor at location R
4
.
For servo-mode inrush control, remove C
3
. Inrush limit will
then be 3.3 Amps. See the HV302/312 data sheet for
details.
Timing
Timing capacitor C
1
determines start-up delay, rise time, and
circuit breaker retry interval,. Changing C
1
will alter these
timings. Refer to the HV302/312 datasheet for the equations
that relate these timings to the value of C
1
. For use in the
equations, the nominal gate threshold voltage (V
GS
) of the
supplied IRFR3710 is 3V and transconductance is about 10
siemens.
Resistors R
8
, R
9
, and R
10
set the delays for PWRGDs B, C,
and D according to the following equation:
t
D
=
1.67µF
R
X
rev 2 12SEP02
2
SUPERTEX [ Supertex, Inc ]
