Supertex inc.
High Voltage DC/DC Converter for
Supertex Ultrasound Transmitter Demoboards
By Afshaneh Brown, Applications Engineer,
and Jimes Lei, Applications Manager
AN-H59
Application Note
The Supertex AN-H59DB1 demoboard is a high voltage
DC/DC converter. It can provide up to +90V voltage supply
for V
PP
and -90V for V
NN
. It also provides +8.0 to +10V
voltage supply for V
DD
, floating power supplies of V
NN
+8.0 to
V
NN
+10V for V
NF
and V
PP
-8.0 to V
PP
-10V for V
PF
. The input
supply voltage is 12V.
The AN-H59DB1 circuitry consists of two high voltage PWM
Current-Mode controllers, a DC/DC transformer driver, and
three low dropout regulators. The Supertex AN-H59DB1
uses a high-voltage, current mode, PWM controller boost
topology to generate +15 to +90V and a high-voltage current
mode PWM controller buck-boost topology to generate -15
to -90V power supply voltage for Supertex HV738DB1 and
HV748DB1 ultrasound transmitter demoboards.
Each of the transmitter demoboards has slightly different
operating voltages as summarized below.
Board
V
PP
V
NN
V
DD
V
PF
V
PP
-8.0V
V
PP
-9.0V
V
NF
V
NN
+8.0V
V
NN
+9.0V
Introduction
To accommodate all three demoboards, the AN-H59DB1
demoboard has adjustable V
PP
, V
NN
, V
DD
, V
PF
and V
NF
. The
purpose of the AN-H59DB1 is to aid in the evaluation of
the three transmitter demoboards. The intention of this
application note is to provide a general circuit description on
how each of the output voltages is generated.
The VSUB pin on the HV738DB1 and HV748DB1 can either
be connected to the most positive supply voltage on the
demoboard, or can be left floating.
To power up the AN-H59DB1, ensure that the 3.3V power
supply will be powered up first, and then the 12V power
supply. The sequences on the HV738DB1 and HV748DB1
took into consideration using the protection diodes on each
power line.
The circuit is shown in Figure 6, the component placement
in Figure 5, and the bill of materials is at the end of this
application note.
HV738DB1 +65V -65V +8.0V
HV748DB1 +75V -75V +9.0V
Application Circuit
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
www.supertex.com
AN-H59
V
PP
Circuit Description
The circuit in Figure 1 shows U5, the Supertex high volt-
age current mode PWM controller, being used to generate
the high voltage power supply for V
PP
. The maximum output
power for V
PP
was set for 10mA at 90V, which is 900mW.
With an input voltage of 12V, a converter frequency of 110
kHz with a 100µH inductor was chosen to provide the de-
sired output power.
The converter frequency is set by an external resistor, R20,
across OSC
IN
and OSC
OUT
pins of U5. A 154kΩ resistor will
set the frequency to about 110 kHz. R24 is the current sense
resistor. 2.2Ω was used to set the maximum peak current
limit to about 450mA. An RC filter, R23 and C15, is added
between the current sense resistor and the current sense
terminal pin 3 of U5. This reduces the leading edge spike on
R24 from entering the current sense pin.
Inductor L1 is being charged from the 12V input by M3.
When M3 turns off, the energy in L1 is discharged into C16,
which is the V
PP
output through D8. The V
PP
voltage is di-
vided down by feedback resistors R25, R26, and R27. The
wiper of R26 is connected to pin 14 of U5. The overall con-
verter will regulate the voltage on pin 14 to 4.0V. Different
V
PP
output voltages can be obtained by adjusting R26.
When the wiper for R26 is set to the top, V
PP
can be calcu-
lated as:
V = V x
R25 + R26 + R27
PP
FB
(
R26 + R27
)
where V
FB
is 4.0V
V
PP
= 4.0V x
(
232k + 100k + 14.3k
)
= 12.1V
100k + 14.3k
R27
When the wiper for R26 is set to the bottom, V
PP
can be
calculated as:
V = V x
R25 + R26 + R27
PP
FB
(
)
V
PP
= 4.0V x
100k
(
232k +14.3k + 14.3k
)
= 96.9V
By adjusting potentiometer R26, V
PP
meets the adjustable
target range of 15 to 90V.
Comparator U6 will turn on LED D7 when the V
PP
output is
out of regulation due to excessive load. During initial power
up, C16 will be at 0V. D7 is therefore expected to be on until
C16 is charged to the desired regulation voltage.
Figure 1: Adjustable V
PP
Power Supply
V
IN
= 12V
R20
154k
8
C12
10µF
OSCIN
OSCOUT
7
L1
100µH
6 VDD
2 VIN
1
D8
MMBD914
V
PP
C16
2.2µF
+15V to +90V
GND
R21
383k
C13
0.1µF
U5
HV9110NG
OUT
4
R23
1.0k
C15
470pF
M3
TN2510
BIAS
SENSE
3
V
IN
D7
LED
R22
3.32k
8
10
5
9
VREF
GND
DISCH
SHUTDOWN
11
R24
2.2
R25
232k
R26
100k
R27
14.3k
1
+
3
2
C14
1.0µF
13
U6
LM2903 4
COMP
RESET
12
14
FB
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
2
Tel: 408-222-8888
www.supertex.com
AN-H59
V
NN
Circuit Description
The circuit in Figure 2 shows U7, the Supertex high voltage
current mode PWM controller, being used to generate the
high voltage power supply for V
NN
. The function of U7 is very
similar to what was described in the V
PP
circuit description
for U5. However, in this circuit a negative voltage is gener-
ated from a positive input voltage source, therefore requir-
ing a buck-boost topology. The maximum output power for
V
NN
was set for -10mA at -90V which is 900mW. With an
input voltage of 12V, a converter frequency of 110 kHz with
a 100µH inductor was chosen to provide the desired output
power.
Inductor L2 is being charged from the 12V input by the par-
allel combination of M6 and M7. When M6 and M7 turn off,
the energy in L2 is discharged into C23, which is the V
NN
output through D10. M6 and M7 are high voltage P-channel
MOSFETs. U7 is designed to drive a high voltage N-chan-
nel MOSFET. The drive output for U7 therefore needs to be
inverted. This is accomplished by M4 and M5.
The feedback voltage that U7 detects on pin 14 is +4.0V.
The V
NN
that needs to be sensed is a negative voltage. A cir-
cuit is needed to make sure the feedback voltage is positive.
This is consists of Q4, Q5, R33, R34, R35, R37, and R38.
Q4 becomes a constant current sink set by the V
NN
voltage
and R35. The same current will be flowing through R33 and
R34.
The voltage on the base of Q5 will be V
IN
minus the voltage
drop across the sum of R33 and R34. By varying R34, the
base voltage on Q5 will change. Q5 becomes a constant
current source with a value set by its base voltage and R37.
The current source of Q5 is going into R38, which creates
a positive voltage that is now proportional to the magnitude
of V
NN
.
R35
V
NN
= V
BE
- (
) x (V
BE
+ V
FB
x
R37
),
R33
+
R34
R38
where V
BE
= 0.6V, V
FB
= 4.0V.
When R34 is set to 100k, V
NN
is calculated to be:
273k
V
NN
= 0.6V - (
) x (0.6V + 4.0V x
14.7k
)
4.99k
+
100k
40.2k
= -4.0V
When R34 is set to 0k, V
NN
is calculated to be:
273k
) x (0.6V + 4.0V x
14.7k
)
V
NN
= 0.6V - (
4.99k
+
0k
40.2k
= -97.4V
By adjusting potentiometer R34, V
NN
meets the adjustable
target range of -15 to -90V.
Comparator U8 will turn on LED D9 when the V
NN
output is
out of regulation due to excessive load. During initial power
up, C23 will be at 0V. D9 is therefore expected to be on until
C23 is charged to the desired regulation voltage.
Figure 2: Adjustable V
NN
Power Supply
V
IN
= 12V
R28
154k
8
6
OSC
IN
VDD
OSC
OUT
7
C20
10µF
C21
10µF
R34
100k
M6, M7
TP2510N8
X2
D10
MMBD914
R33
4.99k
R37
14.7k
Q5
FMMT551
C17
10µF
M4
TP2104K1
R29
383k
C18
0.1µF
2 VIN
1
U7
HV9110NG
OUT 4
BIAS
M5
TN2106K1
Q4
FMMT494
R38
40.2k
R35
237k
VNN
C23
2.2µF
V
IN
= 12V
D9
LED
R30
3.32k
1
8
+
3
2
10
5
9
VREF
GND
DISCH
SENSE 3
R31
1.0k
C22
470pF
L2
100µH
-15V to -90V
GND
U8
4
LM2903
13
C19
1.0µF
COMP
FB
SHUTDOWN
11
R32
2.2
14
RESET 12
R36
10k
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
3
Tel: 408-222-8888
www.supertex.com
AN-H59
VPF and VNF Circuit Description
The three transmitter demoboards require two floating low
voltage supplies, V
PF
and V
NF
. The floating supplies need to
be adjustable to accommodate the different operating re-
quirements for the three different boards. The V
PF
is 8.0 to
10V below the high voltage V
PP
positive supply. The V
NF
is
8.0 to 10V above the high voltage V
NN
negative supply. The
two floating supplies are generated by using two isolated
transformers, T1 and T2, and an isolated transformer driver,
U1, as shown in Figure 4. Both outputs utilize adjustable low
dropout linear regulators, U2 and U3, as shown in Figure 3.
U2 and U3 are both Linear Technology LT1521, which has a
reference voltage of 3.75V on the ADJ pin. For V
PF
, resistors
R6, R7, and R8 set the output V
PF
voltage. R7 is a potentiom-
eter for adjusting V
PF
. V
PF
can be calculated with the following
equation:
V = V x
R6 + R7 + R8
PF
ADJ
Please note that the OUT pin on U2 is referenced to V
PP
,
thereby setting V
PF
to be 8.0 to 10V below V
PP
. V
NF
can also
be calculated in a similar manner using resistors R12, R13,
and R14. Please note that the GND pin on U3 is referenced
to V
NN
thereby setting V
NF
to be 8.0 to 10V above V
NN
.
LED indicators, D5 and D11, start to turn on when the input
current to U2 and U3 reaches an arbitrary value of 40mA.
This is set by Q1 and R3 for V
PF
and Q2 and R9 for V
NF
. The
input current can be calculated with the following equation:
Input current = V
EB
= 0.5V = 41.3mA
R 12.1Ω
50mA current limits are added to protect against output
shorts. The current limiter is consists of a depletion-mode
MOSFET and a series source resistor. The resistor sets the
current limit and can be estimated with the following equa-
tion:
R
SERIES
=
V
TH
x ( √I / I - 1) where,
LIM
DSS
I
LIM
(
R7 + R8
)
When R7 is set to 20kΩ, V
PF
becomes:
V
PF
= 3.75V x
+ 20k + 24.9k
(
45.3k20k + 24.9k
)
= 7.53V
When R7 is set to 0Ω, V
PF
becomes:
V
PF
= 3.75V x
(
45.3k + 0k + 24.9k
0 +24.9k
)
= 10.6V
V
TH
= pinch-off voltage for M1 and M2: -2.5V
I
LIM
= desired current limit: 50mA
I
DSS
= saturation current for M1 and M2: 1.1A
R
SERIES
= 39.3Ω. A 40.2Ω resistor was used.
Figure 3: Adjustable V
PF
and V
NF
Power Supply
R3
12.1
D1
MMBD914
M1
DN3525
R4
40.2
R39
100k
R15
4.99k
D5
LED
C3
10µF
8
OUT 1
IN
R6
45.3k
R7
20k
R8
24.9k
+8.0 to +10V
C4
10µF
U2
LT1521
ADJ 2
5
SHUTDOWN
3,6,7
GND
VPP
V
IN
= 12V
C1
10µF
R1
16.9k
R2
16.9k
13
11
VIN
COLA
3
2
3
9
8
7
Q1
FMMT551
C2
10µF
SHUTDOWN
COLB
14
4
4
R42
1.5k
RSL
7
U1
LT3439
D2
D1
CTX02-16076 MMBD914
VFP
VNF
+8.0 to +10V
C7
10µF
R9
12.1
RT
D3
MMBD914
Q2
FMMT551
C5
10µF
R43
1.5k
M2
DN3525
R11
40.2
R40
100k
8
5
3,6,7
C6
10µF
OUT 1
IN
ADJ 2
SHUTDOWN
GND
U3
LT1521
R12
45.3k
R13
20k
R14
24.9k
6
CT
C11
470µF
5
SYNC
10
GND
1,16
PGND
2
3
4
9
8
7
R10
4.99k
D11
LED
D4
D1
CTX02-16076 MMBD914
VNN
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
4
Tel: 408-222-8888
www.supertex.com
AN-H59
V
DD
Circuit Description
The V
DD
output voltage utilizes an adjustable low dropout lin-
ear regulator, U4 LT1521, as shown in Figure 4. The desired
adjustable output voltage range is 8.0 to 10V to accommo-
date the different operating V
DD
voltages for the three differ-
ent transmitter demoboards.
The LT1521 has a reference voltage of 3.75V on the adj pin.
Resistors R17, R18, and R19 set the output V
DD
voltage.
R18 is a potentiometer for adjusting V
DD
. V
DD
can be calcu-
lated with the following equation:
V
DD
= V
ADJ
x
+ R18 + R19
(
R17R18 + R19
)
When R18 is set to 0Ω, V
DD
becomes:
V
DD
= 3.75V x
(
45.3k + 0k + 24.9k
0 + 24.9k
)
= 10.6V
An LED indicator, D6, is included in case of excessive input,
I
IN
, current. D6 is starts to turn on when the input current
reaches an arbitrary value of 20mA. This is set by Q3 and
R15. When the emitter-base junction of Q3 is forward biased
(0.5V), Q3 will start to turn on, thereby forward biasing D6.
The I
IN
value to turn D6 on can be calculated with the follow-
ing equation:
I
IN
=
V
EB
0.5V
=
= 20.6mA
R15 24.3Ω
When R18 is set to 20kΩ, V
DD
becomes:
V
DD
= 3.75V x
(
45.3k + 20k + 24.9k
20k + 24.9k
)
= 7.53V
Figure 4: Adjustable V
DD
Power Supply
V
IN
= 12V
R15
24.3k
R41
100k
R16
3.32k
D6
LED
C9
10µF
8
OUT
IN
U4
LT1521
ADJ
SHUTDOWN
GND
1
R17
45.3k
R18
20k
R19
24.9k
VDD
Q3
FMMT551
C8
10µF
2
5
3, 6, 7
C10
10µF
+8.0 to 10V
GND
3.3V Input Terminal
The AN-H59DB1 has a 3.3V input terminal that is directly
connected to the output terminal, V
CC
. There is no circuitry
on this board that uses the 3.3V supply. It is only there as a
convenient connection to the 8-pin header. V
CC
is the logic
supply voltage for HV738DB1 and HV748DB1 and can oper-
ate from 1.2 to 5V. However, most users will operate V
CC
at
either 3.0 or 3.3V.
Input and Output Power
The output voltages from the AH-H59DB1 are all generated
from the 12V input line. With no load on the outputs, the
measured input current was about 70mA. This input current
can vary from board to board due to variations in the isolated
transformer.
The maximum output power is:
P
OUT(MAX)
= P
VPP(MAX)
+ P
VNN(MAX)
+ P
VPF(MAX)
+ P
VNF(MAX)
+ P
VDD(MAX)
P
OUT(MAX)
= 0.9W + 0.9W + 0.4W + 0.4W + 0.2W
P
OUT(MAX)
= 2.8W
Under this condition, the 12V input current was measured
to be 340mA. Input power is therefore 4.08W. This gives an
approximate overall efficiency of 69% at full load.
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
5
Tel: 408-222-8888
www.supertex.com
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