As per shown in the below schematic, I have two ADG714(datasheet) octal SPST analog switches connected in the daisy chain configuration.

SchematicIC7 is connected to the STM32F303 controller. connenction of IC7 and the controller as follow:



Enable/CS - Synch

IC8's SCKL, Synch pins are tied with controller and IC7's SCLK and Synch pin respectively. Dout of IC7's is connected to Din of IC8 through 4.7k ohms pull-up resistor because Dout is open drain. SLCK is of 18Mhz. Supply voltage:

Vss : -2.5V

Vdd: 3.3V

as per datasheet, abosolute operating condition Vdd to Vss is 7V

Configuration of the controller's SPI as follow: Half duplex transmitter, 16bits data frame, CPOL = 0, clock phase is negative edge, MSB first and Enable or CS or Synch is controlled through GPIO pin.

I am not getting correct Dout output which should be 8 bits delayed as per the datasheet. Below image is of Logic Analyser.

Channel0 is SCKL

Channel1: MOSI

Channel2: Synch/Enable/CS

channel3: Dout of IC7


Could you please tell me where I have made mistakes?

EDIT: is it also possible that Pull up resistor's value is high and because of parasitic capacitance, time constant is high and switch can not 'drive' the output correctly? as per the datasheet, sclk raise time to Dout valid output max time is 20ns ..


  • \$\begingroup\$ Maximum is not the same as recommended. Be aware you are pushing device limits. \$\endgroup\$
    – DKNguyen
    Dec 14, 2020 at 14:50
  • \$\begingroup\$ I have changed pull up resistor from 4.7K to 470 ohms and it worked. I am afraid that current is withing its limit. How should I check in datasheet? datasheet says, LOGIC OUTPUT, (SDA) Output Voltage Low, VOL = 0.6v Max with test condition Isink = 6mA does it mean that minimum Pull up value id 0.6/6mA = 100 ohms? so 470 ohms can be used as pull up? \$\endgroup\$ Dec 14, 2020 at 15:41


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