SI8711CD-B-IM datasheet(15/36 Pages) SILABS

15 / 36 page

Si87xx

Preliminary Rev. 0.5

New designs should consider the input circuit configurations of Figure 9, which are more efficient than those of

Figures 7 and 8. As shown, S1 and S2 represent any suitable switch, such as a BJT or MOSFET, analog

transmission gate, processor I/O, etc. Also, note that the Si87xx input can be driven from the I/O port of any MCU

or FPGA capable of sourcing a minimum of 6 mA (see Figure 9B). Additionally, note that the Si87xx propagation

delay and output drive do not significantly change for values of IF between IF(MIN) and IF(MAX).

Figure 9. Si87xx Other Input Circuit Configurations

4.2. Output Circuit Design and Power Supply Connections

The speed of the open collector circuit is dependent upon the supply, VCC, the pullup resistor, RL, and the load

modeled by CL. Figure 10 illustrates three common circuit output configurations. For VDD = 5 V operation,

RL>350 is recommended to ensure proper VOL levels. For VDD = 30 V operation, RL > 2.1 kis recommended

to ensure proper VOL levels. If the enable pin is used (see Figure 10B) and two separate supplies power VDD and

the VO pullup resistor, the enable pin should be referenced to the VDD pin because VO cannot exceed VDD by more

than 0.5 V. Figure 10C illustrates a circuit using the internal 20 k

 resistor.

Note that GND can be biased at, above, or below ground as long as the voltage on VDD with respect to GND is a

maximum of 30 V. VDD decoupling capacitors should be placed as close to the package pins as possible. The

optimum values for these capacitors depend on load current and the distance between the chip and its power

source. It is recommended that 0.1 and 1 µF bypass capacitors be used to reduce high-frequency noise and

maximize performance. Opto replacement applications should limit their supply voltages to 30 V or less.

Figure 10. Si87xx Output Circuit Configurations

Si87xx

+5V

Control

Input

N/C

ANODE

CATHODE

N/C

Si87xx

N/C

CATHODE

MCU I/O

Port pin

ANODE

N/C

Si87xx

GND

VDD

0.1, 1 µF

VCC1 3-30 V

VCC2 3-30 V

GND

0.1, 1 µF

VCC 3-30 V

VDD

Si87xx

GND

VDD

0.1, 1 µF

VCC 3-30 V

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