6

FN8239.1

January 21, 2005

ISL88694 Operation

To improve the operation of the SMBus where larger bus

capacitance exists, the ISL88694 provides active pull-up

using switched current sources. When the bus is idle and

both lines are HIGH, a standby pull-up current of 100µA is

used to maintain the signal level while minimizing power

consumption. When either of the two signals is pulled LOW,

noise margin.

When the bus line is released, it is pulled high by the

ISL88694 active current until the voltage exceeds the

combination filters out noise on the signal line. Once the

ISL88694 detects a valid rising edge, a 2.2mA boost current

pulls the bus line high very quickly (see Figure 8). This boost

threshold and the pull-up current returns to the active level. If

both inputs are HIGH, the pull-up current drops to the

standby level of 100µA.

FIGURE 8. ISL88694 SMBus SYSTEM BOOST PULL-UP

5.5V).

FIGURE 9. ISL88694 SMBus SYSTEM BOOST PULL-UP

2.7V).

FIGURE 10. NOISE SUPPRESSION. BOOST CURRENT

APPLIED WHEN INPUT SIGNAL EXCEEDS 20Vns

(TYPICAL).

With RC

Pullup

With ISL88694 SMA

R=15.8K

C= 200pF

With RC

Pullup

With ISL88694 SMA

R=15.8K

C= 200pF

Gnd

t

SMBus1

>20Vns

SMBus2

With SMA

Without SMA

(Typical)

ISL88694