ISL71841SEHLSLASHPROTO datasheet(24/30 Pages) RENESAS

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ISL71841SEH

FN8735 Rev. 7.00

Page 24 of 30

Feb 23, 2018

Applications Information

Power-Up Considerations

The circuit is designed to be insensitive to any given power-up

sequence between V+, V-, and VREF; however, it is recommended

that all supplies power up relatively close to each other.

Overvoltage Protection

The ISL71841SEH has overvoltage protection on both the input

and the output. On the output, the voltage is limited to a diode

past the rails. Each of the inputs has independent overvoltage

protection that works regardless of the switch being selected. If a

switch experiences an overvoltage condition (3V to 4V past the

rail), the switch is turned off. As soon as the voltage returns

within the rails, the switch returns to normal operation.

VREF and Logic Functionality

The VREF pin sets the logic threshold for the ISL71841SEH. The

range for VREF is between 4.5V and 5.5V with a nominal voltage

of 5V. The address pins and enable are compared against

roughly 30% of VREF voltage (refer to Figure 80). With 5.0V on

VREF, the switching point is set to around 1.4V. This switching

point allows for both 5V and 3.3V logic control.

Considerations for Redundant Applications

When using the ISL71841SEH in a cold sparing application, it is

recommended to keep the ground pin connected to system

ground at all times. All supply pins (V+, V-, and VREF) should

either be grounded or floating together.

If the supply pins are floating, it is recommended to place a high

value bleed resistor (~1MΩ) in parallel with the decoupling

capacitors on each supply pin to ensure that the supply voltage is

discharged in a predictable manner. Figures 81 and 82 illustrate

the recommended cold sparing setup for both shorted or floating

supplies.

ISL71841SEH vs ISL71840SEH

The ISL71840SEH, a 16-channel version of the ISL71841SEH, is

available in a 28 Ld CDFP. The parts’ performance specifications

are very similar. Apart from the apparent increase in channel

density, the ISL71841SEH has slightly higher output leakage

compared to the ISL71840SEH because it has more channels

connected to the output. The supply current for the ISL71841SEH

is also slightly higher compared to the ISL71840SEH. Refer to

Table 1 on page 3 for a comparison of the two devices.

400kΩ

200kΩ

ISL71841SEH

A/EN

VREF

TO DECODER

FIGURE 80. SIMPLIFIED VREF CIRCUITRY

FIGURE 81. COLD SPARING SETUP WITH SUPPLIES SHORTED

FIGURE 82. COLD SPARING SETUP WITH SUPPLIES FLOATING

SUPPLY PIN

SYSTEM VOLTAGE

SUPPLY PIN

SYSTEM VOLTAGE

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