9.2.2.2 Detailed Design Procedure

9.2.2.2.1 Sizing Pullup Resistors

The pullup resistor value should 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 pullup resistor value is calculated as:

( )

( )

Pullup voltage V

0.35 V

Resistor value

0.015 A

-

W =

(2)

Table 9-2 provides resistor values for various reference voltages and currents at 15 mA, 10 mA, and 3 mA. The

resistor value 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 of the GTL device at 0.175 V, although the 15 mA only applies to current flowing through

the SN74GTL2003.

Table 9-2. Pullup Resistor Values(1) (2) (3) (4)

PULLUP RESISTOR VALUE (Ω)

VOLTAGE

15 mA

10 mA

3 mA

NOMINAL

+10%

NOMINAL

+10%

NOMINAL

+10%

5.0 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

(1)

H = HIGH voltage level, L = LOW voltage level, X = do not care.

(2)

Calculated for VOL = 0.35 V

(3)

Assumes output driver VOL = 0.175 V at stated current

(4)

+10% to compensate for VDD range and resistor tolerance

9.2.3 Unidirectional Up Translation

For unidirectional up translation (lower voltage to higher voltage), the reference transistor is connected the same

as for a down translation. A pullup resistor is required on the higher voltage side (Dn or Sn) to get the full HIGH

level, because the GTL device only passes the reference source (SREF) voltage as a HIGH when doing an up

translation. The driver on the lower voltage side only needs pullup resistors if it is open drain.

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SN74GTL2003

SCDS305D – FEBRUARY 2011 – REVISED SEPTEMBER 2022

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