HV57009
Typical Current Programing Circuits
0.1µF
VDD
0.1µF
VDD
HV57009
VBP
VBP
To other
outputs
Logic
- +
IOUT
HVOUT
+IN
-IN
VSS
REXT
IREF
VREF
R
D
*10KΩ
C
D
*390pF
HV57009
To other
outputs
Logic
- +
IOUT
HVOUT
+IN
-IN
VSS
VREF
REXT
IREF
R
D
*10KΩ
C
D
* 390pF
Figure 1a: Negative Control
Figure 1b: Positive Control
*Required if R
EXT
> 10KΩ or R
EXT
is replaced by a constant current source.
Since I
OUT
= I
REF
=
V
REF
R
EXT
Given I
OUT
and V
REF
, the R
EXT
can be calculated by using:
R
EXT
=
V
V
REF
=
REF
I
OUT
I
REF
Therefore:
If I
OUT
= 2.0mA and V
REF
= -5.0V → R
EXT
= 2.5KΩ.
If I
OUT
= 1.0mA and R
EXT
= 1.0KΩ → V
REF
= -1.0V.
If R
EXT
>10KΩ, add series network R
D
and C
D
to ground for
stability as shown.
This control method behaves linearly as long as the opera-
tional amplifier is not saturated. However, it requires a nega-
tive power source and needs to provide a current I
REF
= I
OUT
for each HV570 chip being controlled.
If HV
OUT
≥ +1.0V, the HV
OUT
cascode may no longer oper-
ate as a perfect current source, and the output current will
diminish. This effect depends on the magnitude of the output
current.
4
The intersection of a set of I
OUT
and V
REF
values can be lo-
cated in the graph shown below. The value picked for R
EXT
must always be in the shaded area for linear operation. This
control method has the advantage that V
REF
is positive, and
draws only leakage current. If R
EXT
> 10KΩ, add series net-
work R
D
and C
D
to ground for stability as shown.
Note:
Lower reference current I
REF
, results in higher distortion,
∆I
CS
, on the output.
HV570 I
OUT
vs. V
REF
0.1K
0.2K
0.5K
1K
2K
3K
3
I
O U T
(mA)
2
5K
1
0
0
1
2
V
REF
(Volts)
3
4
5
6
SUPERTEX [ Supertex, Inc ]
