lm96530sqx National Semiconductor Corporation, lm96530sqx Datasheet - Page 6

• Manufacturer Part Number: lm96530sqx
• Description: Lm96530 Ultrasound Transmit/receive Switch
• Manufacturer: National Semiconductor Corporation

www.national.com
Functional Description
The LM96530 RX switch provides an 8-channel receive side
interface solution for medical ultrasound applications suitable
for integration into multi-channel (128 / 256 channel) systems.
A functional block diagram of the IC is shown in . Each RX
switch channel on the IC has a high-voltage input that can be
directly connected to a transducer driven by a high-voltage
pulser, such as the LM96550. The input feeds into a diode
bridge with its output being diode-clamped to ± 0.7V. The
diode bridge bias current is set to 1 mA with Rref = 50KΩ.
Therefore, the output can be directly connected to a low noise
amplifier (LNA) stage which must be protected from the high-
voltage signals on the transducer.
The bias current of the bridge is determined by two equally-
sized current sources with their current value ranging be-
tween 0 and 8mA depending on the external resistor Rref at
the input of the bandgap reference block. While the bias cur-
rent is the same value for all channels on the IC, each channel
can be switched on and off individually with an 8–bit shift reg-
ister that is programmed via a SPI™ compatible bus.
The on-chip analog circuitry requires dual 5V supplies VDD
and VSS, a single logic supply VLL, and a high voltage neg-
ative bias, VSUB.
FIGURE 2. Block Diagram of T/R Channel
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Its diode-bridge-based architecture allows high-speed low-
distortion channel designs targeting low-power, portable sys-
tems. A complete system can be designed using National’s
companion LM965XX chipset.
SERIAL INTERFACE OPERATION
The digital interface is comprised of an 8-bit shift register and
a latch. Each bit controls one T/R switch channel, where the
MSB bit, i.e., the first bit written (D7) controls channel 7, and
the LSB bit (D0) controls channel 0. The three input pins, SDI,
SCSI and SCKl, are all Schmitt Trigger inputs with 0.5V typical
hysteresis. The output pins SDO, SCSO, and SCLKO are
SPI™ compatible. The serial data input SDI is synchronously
read into the shift register on the rising edge of the clock SCKI.
When SCSI changes from low to high, the data in the shift
register is transferred to the latch circuit, and output on the
parallel data signals P0 through P7 which drive the switched
bias current sources for channels n=0,…, 7, respectively.
When SCSI changes from high to low, the latch output Pn,
and thus the biasing condition, does not change.
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