UCA9306L-S08-R datasheet(8/9 Pages) UTC

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UCA9306

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

8 of 9

www.unisonic.com.tw

QW-R140-004.b



DETAILED DESIGN PROCEDURE

Bidirectional Voltage Translation

For the bidirectional clamping configuration (higher voltage to lower voltage or lower voltage to higher voltage), the

EN input must be connected to VREF2 and both pins pulled to high-side VDPU through a pullup resistor (typically

200kΩ). This allows VREF2 to regulate the EN input. A100-Pf filter capacitor connected to VREF2 is recommended. The

2C bus master output can be push-pull or open-drain (pull up resistors may be required) and the I2C bus device

output can be totem pole or open-drain (pull up resistors are required to pull the SCL2 and SDA2 outputs to VDPU) .

However , if either output is push-pull , data must be unidirectional or the outputs must be 3-state capable and be

controlled by some direction-control mechanism to prevent high-to-low contentions in either direction . If both outputs

are open-drain , no direction control is needed.

The reference supply voltage(VREF1) is connected to the core power-supply voltage of the processor.

Design Requirements

PARAMETER

SYMBOL

MIN

TYP

(1)

MAX

UNIT

Reference voltage

VREF2

VREF1+0.6

2.1

Enable input voltage

VREF1+0.6

2.1

Reference voltage

VREF1

1.2

1.5

4.4

Pass switch current

IPASS

Reference-transistor current

IREF

μA

Note: All typical values are at TA=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

15mA.This ensures a pass voltage of 260 mV to 350 mV. If the current through the pass transistor is higher than

15mA, the pass voltage also is higher in the on state. To set the current through each pass transistor at 15mA, the

pullup resistor value is calculated as:

DPU

V- 0.35V

0.015A

The following table summarizes resistor values, reference voltages, and currents at 15mA, 10 mA, and 3mA. The

resistor value shown in the +10%column (or a larger value) should be used to ensure that the pass voltage of the

transistor is 350mV or less. The external driver must be able to sink the total current from the resistors on both sides

of the UTC UCA9306 device at 0.175V, although the 15 mA applies only to current flowing through the UTC

UCA9306

device.

Pullup Resistor Values

PULLUP RESISTOR VALUE (Ω)

15mA

10mA

3mA

VDPU

NOMINAL

+10%

NOMINAL

+10%

NOMINAL

+10%

310

341

465

512

1550

1705

3.3V

197

217

295

325

983

1082

2.5V

143

158

215

237

717

788

1.8V

106

145

160

483

532

1.5V

115

127

383

422

1.2V

283

312

(1) Calculated for VOL=0.35V

(2) Assumes output driver VOL=0.175V at stated current

(3) +10%to compensate for VDD range and resistor tolerance

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