PCA9306
http://onsemi.com
8
Table 8. APPLICATION OPERATING CONDITIONS Refer to Figure 6.
Symbol Parameter Conditions Min Typ(1) Max Unit
Vbias(ref)(2) Reference Bias Voltage (2) Vref(1) + 0.6 2.1 5 V
VI(EN) EN Pin Input Voltage Vref(1) + 0.6 2.1 5 V
Vref(1) Reference Voltage (1) 0 1.5 4.4 V
Isw(pass) Pass Switch Current 14 mA
Iref Reference Current Transistor 5 mA
Tamb Ambient Temperature Operating in free−air −55 +125 °C
11.All typical values are at Tamb = 25 °C.
Sizing Pull−up Resistor
The pull−up resistor value needs to limit the current
through the pass transistor when it is in the ON state to about
15 mA. This ensures a pass voltage of 260 mV to 350 mV.
If the current through the pass transistor is higher than
15 mA, the pass voltage also is higher in the ON state. To set
the current through each pass transistor at 15 mA, the
pull−up resistor value is calculated as:
RPU +
VPU(D) *0.35 V
0.015 A (eq. 1)
The following table summarizes resistor reference
voltages and currents at 15 mA, 10 mA, and 3 mA. The
resistor values shown in the +10% column or a larger value
should be used to ensure that the pass voltage of the
transistor would be 350 mV or less. The external driver must
be able to sink the total current from the resistors on both
sides o f the PCA9306 device at 0.175 V, although the 15 mA
only applies to current flowing through the PCA9306
device.
Table 9. PULLUP RESISTOR VALUES Calculated for VOL = 0.35 V; assumes output driver VOL = 0.175 V at stated current.
Vpu(D)
Pullup Resistor Value (W)
15 mA 10 mA 3 mA
Nominal +10% (Note 12) Nominal +10%(1) Nominal +10% (Note 12)
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
12.+10% to compensate for VCC range and resistor tolerance.
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:
•Keep trace length to a minimum by placing the
PCA9306 close to the processor.
•The trace length should be less than half the time of
flight to reduce ringing and reflections.
•The faster the edge of the signal, the higher the chance
for ringing.
•The higher the drive strength (up to 15 mA), the higher
the frequency the device can 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 i s 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.