HV257
Power Up/Down Issues
External Diode Protection
The device can be damaged due to improper power up / down
sequence. To prevent damage, please follow the acceptable power
up / down sequences, and add two external diodes as shown in
the diagram on the right. The first diode is a high voltage diode
across V
PP
and V
DD
, where the anode of the diode is connected
to V
DD
and the cathode of the diode is connected to V
PP
. Any low
current, high voltage diode, such as a 1N4004, will be adequate.
The second diode is a Schottky diode across V
NN
and D
GND
, where
the anode of the Schottky diode is connected to V
NN
, and the
cathode is connected to D
GND
. Any low current Schottky diode such
as a 1N5817 will be adequate.
External Diode Protection Connection
V
DD
1N4004 or similar
V
PP
V
NN
1N5817 or similar
D
GND
Suggested Power Up/Down Sequence
The HV257 needs all power supplies to be fully up and all channels
refreshed with V
SIG
= 0V to force all high voltage outputs to 0V.
Before that time, the high voltage outputs may have temporary
voltage excursions above or below Gnd level depending on selected
power up sequence. To minimize the excursions:
1. The V
DD
and V
NN
power supplies should be applied at the same
time (or within a few nanoseconds).
2. All channels should be continuously refreshed with
V
SIG
= 0V, just before, and while the V
PP
is ramping up.
Suggested V
PP
ramp up speed should be 10msec or longer and
ramp down to be 1msec or longer.
Acceptable Power Up Sequences
The HV257 can be powered up with any of the following sequences
listed below.
1) V
PP
2) V
NN
3) V
DD
4) Inputs and Anode
1) V
NN
2) V
DD
3) V
PP
4) Inputs and Anode
1) V
DD
& V
NN
2) Inputs 3) V
PP
4) Anode
Acceptable Power Down Sequences
The HV257 can be powered down with any of the following
sequences listed below.
1) Inputs and Anode 2) V
DD
3) V
NN
4) V
PP
1) Inputs and Anode 2) V
PP
3) V
DD
4) V
NN
1) Anode 2) V
PP
3) Inputs 4) V
NN
& V
DD
Recommended Power Up/Down Timing
A
0
- A
4
EN
300V
0
1
2 31
0
0
1
2
V
PP
V
DD
V
NN
V
SIG
HV
OUT
Gnd +/- V offset X 72
0V
6.5V
0V
0V
-5.5V
0V
0V
HV
OUT
Level at Power UP
V
PP
V
DD
V
NN
Power Up Sequence
V
DD
Before V
NN
0V
V
NN
Before V
DD
V
PP
V
DD
V
NN
0V
6.5V
0V
6.5V
0V
0V
-5.5V
0V
-5.5V
HV
OUT
0V
-5.5V
HV
OUT
6.5V
0V
5
SUPERTEX [ Supertex, Inc ]
