6
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 VPP and VDD, where the anode of the
diode is connected to VDD and the cathode of the diode
is connected to VPP. Any low current, high voltage diode,
such as a 1N4004, will be adequate. The second diode is a
Schottky diode across VNN and DGND, where the anode of
the Schottky diode is connected to VNN, and the cathode is
connected to DGND. Any low current Schottky diode such
as a 1N5817 will be adequate.
Acceptable Power Up Sequences
The HV257 can be powered up with any of the following
sequences listed below.
1) VPP 2) VNN 3) VDD 4) Inputs and Anode
1) VNN 2) VDD 3) VPP 4) Inputs and Anode
1) VDD & VNN 2) Inputs 3) VPP 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) VDD 3) VNN 4) VPP
1) Inputs and Anode 2) VPP 3) VDD 4) VNN
1) Anode 2) VPP 3) Inputs 4) VNN & VDD
External Diode Protection Connection
Suggested Power Up/Down Sequence
The HV257 needs all power supplies to be fully up and all
channels refreshed with VSIG = 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 VDD and VNN power supplies should be applied at
the same time (or within a few nanoseconds).
2. All channels should be continuously refreshed with
VSIG = 0V, just before, and while the VPP is ramping up.
Suggested VPP ramp up speed should be 10msec or longer
and ramp down to be 1msec or longer.
VDD VPP
1N4004 or similar
VNN DGND
1N5817 or similar
Recommended Power Up/Down Timing
0V
VNN
6.5V
-5.5V
0V
300V
0V
HVOUT
0V
VSIG
0 1 2 31 0 0 1 2
Gnd +/- V offset X 72
0V
EN
0V
6.5V
-5.5V
0V
VDD
VPP
300V
0V
0V
A0 - A4
Gnd +/- V offset X 72
0V
HVOUT Level at Power Up
Power Up Sequence
VNN Before VDD
0V
VNN
6.5V
-5.5V
-5.5V
0V
VDD
VPP0V
HVOUT 0V
0V
VNN
6.5V
6.5V
-5.5V
0V
VDD
VPP0V
HVOUT
0V
VDD Before VNN