Microchip HV7355DB1 Manual
Microchip
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HV7355DB1
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Supertex inc.
Supertex inc.
www.supertex.com
HV7355DB1
Doc.# DSDB-HV7355DB1
B070314
General Description
The HV7355 is a monolithic eight-channel, high-speed,
high voltage, unipolar ultrasound transmitter pulser.
This integrated, high performance circuit is in a single,
8x8x0.9mm, 56-lead QFN package.
The HV7355 can deliver guaranteed ±1.5A source and sink
current to a capacitive transducer with 0 to +150V peak
voltage. It is designed for medical ultrasound imaging and
ultrasound material NDT applications. It can also be used
as a high voltage driver for other piezoelectric or capacitive
MEMS transducers, or for ATE systems and pulse signal
generators as a signal source.
The HV7355’s circuitry consists of controller logic circuits,
level translators, gate driving buffers and a high current and
high voltage MOSFET output stage. The output stages of
each channel are designed to provide peak output currents
typically over ±1.5A for pulsing, with up to 150V swings. The
upper limit frequency of the pulser waveform is dependent
upon the load capacitance. With different capacitance load
conditions the maximum output frequency is about 20MHz.
This demoboard datasheet describes how to use the
HV7355DB1 to generate the basic high voltage pulse
waveform as an ultrasound transmitting pulser.
The HV7355 circuit uses DC-coupling from a 3.3V logic input
to output TX0~7 internally, therefore the chip needs three
sets of voltage supply rails: VLL (+3.3V), VDD/VSS (+/-5.0V)
and VPP (up to +150V). The VPP high voltage supply can be
changed rather quickly, compared to the capacitor gate-
coupled driving pulsers. This direct coupling topology of the
gate drivers not only saves two high voltage capacitors per
channel, but also makes the PCB layout easier.
The control signal logic-high voltage should be the same
as the VLL voltage of the IC, and the logic-low should be
referenced to GND.
The HV7355DB1 output waveforms can be displayed using
an oscilloscope by connecting the scope probe to the test
points TX0~7 and GND. The soldering jumper can select
whether or not to connect the on-board dummy load, a
330pF capacitor paralleling with a 2.5kΩ resistor. The test
points can be used to connect the user’s transducer to easily
evaluate the pulser.
Block Diagram
150V, 1.5A, Unipolar
Ultrasound Pulser Demoboard
LT
IN0
IN7
VLL
GND
MC
VSS
VSS
+5.0 to 150V+3.3V
CPF VPPVDD
VPF
CWD
Q[7:0]
LT
LT
LT
-5.0V
D0
SDI
Q7
SDO
SCK
SET
LE
CS
EN PWR
RGND
RGND
RGND
SUB
Q7
Q0
AVDD
VSUB
TX0
R3
2.5k
C4
330pF
GND
Dummy
Load
R2
Waveform
Generator
CPLD
+3.3V
OSC
JTAG
EXCLK
EN
CLKIN
WAVE
FREQ
SEL
EN
CW/RTZ
CW
LR
RTZ
PWR
EN
40MHz
6
TX7
LR
VDD
VDD VPP
VDD
VDD
VDD
VDD
VPF
VPF
VPP
TX7
VPP
+5.0V
2
HV7355DB1
Supertex inc.
www.supertex.com
Doc.# DSDB-HV7355DB1
B070314
The PCB Layout Techniques
The large thermal pad at the bottom of the HV7355 package
is internally connected to the IC’s substrate (VSUB). This
thermal pad should be connected to 0V or GND externally
on the PCB. The designer needs to pay attention to the con-
necting traces on the outputs TX0~7, as the high-voltage
and high-speed traces. In particular, controlled-impedance
to the ground plane and more trace spacing needs to be ap-
plied in this situation.
High-speed PCB trace design practices that are compatible
with about 50 to 100MHz operating speeds are used for the
demo board PCB layout. The internal circuitry of the HV7355
can operate at quite a high frequency, with the primary speed
limitation being load capacitance. Because of this high
speed and the high transient currents that result when driv-
ing capacitive loads, the supply voltage bypass capacitors
and the driver to the FET’s gate-coupling capacitors should
be as close to the pins as possible. The GND pin should
have low inductance feed-through via connections that are
connected directly to a solid ground plane. The VDD, VSS,
VPP and CPP voltage-supply and/or bypass capacitor pins
can draw fast transient currents of up to 2.0A, so they should
be provided with a low-impedance bypass capacitor at the
chip's pins. A ceramic capacitor of 1.0 to 2.0µF may be used.
Only VPP to GND capacitors need be high voltage. CPF to
VPP capacitors only need be low voltage. Minimize the trace
length to the ground plane, and insert a ferrite bead in the
power supply lead to the capacitor to prevent resonance in
the power supply lines. For applications that are sensitive
to jitter and noise when using multiple HV7355 ICs, insert
another ferrite bead between each chips supply line.
Pay particular attention to minimizing trace lengths and
using sufcient trace width to reduce inductance. Surface
mount components are highly recommended. Since the out-
put impedance of the HV7355’s high voltage power stages
is very low, to obtain better waveform integrity at the load
terminals after long cables, in some cases it may be desir-
able to add a small value resistor in series with the outputs
TX0~7. This will, of course, reduce the output voltage slew
rate at the terminals of a capacitive load. Be aware of the
parasitic coupling from the outputs to the input signal termi-
nals of the HV7355.
This feedback may cause oscillations or spurious waveform
shapes on the edges of signal transitions. Since the input
operates with signals down to 3.3V, even small coupling
voltages may cause problems. Use of a solid ground plane
and good power and signal layout practices will prevent this
problem. Also ensure that the circulating ground return cur-
rent from a capacitive load cannot react with common induc-
tance to create noise voltages in the input logic circuitry.
Testing the Integrated Pulser
The HV7355 pulser demoboard should be powered up with
a DC power supplie that has current limiting functions.
To meet the typical loading conditions, the on-board dummy
load 330pF//2.5kΩ should be connected to the high voltage
pulser output through the solder jumper when using an oscil-
loscope’s high impedance probe. To evaluate different load-
ing conditions, the values of the RC within the current and
power limit of the device may be changed.
In order to drive the user’s piezo transducers with a cable,
one should match the output load impendence properly to
avoid cable and transducer reections. A 70 to 75Ω coaxial
cable is recommended. The coaxial cable end should be sol-
dered to TX0~7 and GND directly with very short leads. If a
user’s load is being used, the on-board dummy load should
be disconnected by cutting the small shorting copper trace in
between the zeroΩ resistor’s (R2, R12 etc.) pads. They are
shorted by factory default.
All of the on-board test points are designed to work with the
high impedance probe of the oscilloscope. Some probes
may have limited input voltage. When using the probe on
these high voltage test-points, make sure that VPP voltages
do not exceed the probe limit. Using the high impendence
oscilloscope probe for the on-board test points, it is impor-
tant to have short ground leads to the circuit board ground
plane.
Produkt Specifikationer
| Mærke: | Microchip |
| Kategori: | Ikke kategoriseret |
| Model: | HV7355DB1 |
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