HV57009
Typical Current Programing Circuits
VDD
VDD
0.1µF
0.1µF
HV57009
HV57009
VBP
VBP
To other
outputs
To other
outputs
Logic
Logic
IOUT
-
+
IOUT
-
+
HVOUT
HVOUT
+IN
-IN
+IN
-IN
VSS
VSS
RD*10KΩ
CD*390pF
REXT
IREF
RD*10KΩ
C *
REXT
IREF
VREF
390pF
D
VREF
Figure 1b: Positive Control
*Required if REXT > 10KΩ or REXT is replaced by a constant current source.
Figure 1a: Negative Control
VREF
REXT
Since IOUT = IREF
Therefore:
=
Given IOUT and VREF, the REXT can be calculated by using:
VREF
IREF
VREF
IOUT
If IOUT = 2.0mA and VREF = -5.0V → REXT = 2.5KΩ.
If IOUT = 1.0mA and REXT = 1.0KΩ → VREF = -1.0V.
REXT
=
=
If REXT >10KΩ, add series network RD and CD to ground for
stability as shown.
The intersection of a set of I
and VREF values can be lo-
cated in the graph shown beOloUTw. The value picked for REXT
must always be in the shaded area for linear operation. This
This control method behaves linearly as long as the opera- control method has the advantage that V is positive, and
tional amplifier is not saturated. However, it requires a nega- draws only leakage current. If REXT > 10KRΩEF, add series net-
tive power source and needs to provide a current IREF = IOUT work RD and CD to ground for stability as shown.
for each HV570 chip being controlled.
Note:
If HVOUT ≥ +1.0V, the HVOUT 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.
Lower reference current IREF, results in higher distortion,
∆ICS, on the output.
HV570 IOUT vs. VREF
4
3
2
1
0
0.1K
0.2K
0.5K
1K
2K
3K
5K
0
1
2
3
4
5
VREF (Volts)
6
SUPERTEX [ Supertex, Inc ]
