HV2802 datasheet(14/26 Pages) MICROCHIP

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HV2802/HV2902

DS20005449A-page 14

 2015 Microchip Technology Inc.

4.0

DETAILED DESCRIPTION AND

APPLICATION INFORMATION

The high-voltage analog switches are used for

multiplexing a piezoelectric transducer array in a probe

to multiple channel transmitters (Tx) arrays in a medical

ultrasound system.

Figure 4-1 shows a typical medical ultrasound image

system comprising 64-channels of transmit pulsers,

64-channels of receivers (LNA and ADC) and

64-channels of T/R switches connecting to 192

elements of an ultrasound transducer probe via a

high-voltage analog switch array.

FIGURE 4-1:

Typical Medical Ultrasound Imaging System.

The HV2802/HV2902 devices are comprised of two

main circuitries:

• A low-power CMOS digital serial interface

analog switches

• High-voltage bilateral analog switch.

High-voltage supplies VPP and VNN are needed by the

high-voltage level translation circuitry to control the

states of the output high-voltage analog switches. In

addition, each high-voltage analog switch can be

independently controlled because each switch is

controlled via a corresponding latch. A 32-bit shift

data into the registers, and after completion, to load the

data onto the latches that control the states of the

high-voltage analog switches.

The HV2802/HV2902 have a digital serial interface

consisting of logic signals, Data In (DIN), Clock (CLK),

Data Out (DOUT), Latch Enable (LE) and Clear (CLR).

The digital circuits are supplied by VDD and either a

3.3V or a 5V logic can be used. With a VDD = 5V supply,

the serial clock frequency can operate up to 20 MHz.

The data is shifted into the shift registers on the rising

edge (low-to-high transition) of the clock. The switch

configuration bit of SW31 is shifted in first and the

switch configuration bit of SW0 is shifted in last. To

avoid clock feedthrough, the latch enable input (LE)

should remain high while the 32-bit data-in signal is

shifted into the 32-bit register. After the valid 32-bit data

complete shifting into the shift registers, the high-to-low

transition of the LE signal transfers the contents of the

shift register into the latches. Finally, setting the LE high

again allows all the latches to keep the current state,

while new data can now be shifted into the shift

registers without upsetting the latches.

It is recommended to change all the latch states at the

same time through this method to avoid possible clock

feedthrough noise. See Figure 4-2 for details.

ADC

FPGA Ctrl Logic

VIDEO

CPU

MEMORY

T/R

Switch

T/R

Switch

T/R

Switch

CH64

CH2

CH1

PZT Array

HV 2XXX SW Array

Tx / Rx Array

E65

E192

E128

E129

E66

E130

E64

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