PCA9306

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© NXP B.V. 2010. All rights reserved.

Product data sheet

Rev. 6 — 25 November 2010

11 of 26

NXP Semiconductors

PCA9306

[1]

11.2.1 Maximum frequency calculation

The maximum frequency is totally dependent upon the specifics of the application and the

device can operate > 33 MHz. Basically, the PCA9306 behaves like a wire with the

additional characteristics of transistor device physics and should be capable of performing

at higher frequencies if used correctly.

Here are some guidelines to follow that will help maximize the performance of the device:

reflections.

use.

In a 3.3 V to 1.8 V direction level shift, if the 3.3 V side is being driven by a totem pole type

driver no pull-up resistor is needed on the 3.3 V side. The capacitance and line length of

concern is on the 1.8 V side since it is driven through the ON resistance of the PCA9306.

If the line length on the 1.8 V side is long enough there can be a reflection at the

chip/terminating end of the wire when the transition time is shorter than the time of flight of

the wire because the PCA9306 looks like a high-impedance compared to the wire. If the

wire is not too long and the lumped capacitance is not excessive the signal will only be

slightly degraded by the series resistance added by passing through the PCA9306. If the

lumped capacitance is large the rise time will deteriorate, the fall time is much less

affected and if the rise time is slowed down too much the duty cycle of the clock will be

degraded and at some point the clock will no longer be useful. So the principle design

consideration is to minimize the wire length and the capacitance on the 1.8 V side for the

clock path. A pull-up resistor on the 1.8 V side can also be used to trade a slower fall time

for a faster rise time and can also reduce the overshoot in some cases.

Table 10.

Pull-up resistor values

Pull-up resistor value (

Ω)

15 mA

10 mA

3mA

Nominal

+10 %[1]

Nominal

+10 %[1]

Nominal

+10 %[1]

5 V

310

341

465

512

1550

1705

3.3 V

197

217

295

325

983

1082

2.5 V

143

158

215

237

717

788

1.8 V

97

106

145

160

483

532

1.5 V

77

85

115

127

383

422

1.2 V

57

63

85

94

283

312