(Limits are 100% production tested at TA = +25°C and/or TA = +85°C. Limits over the operating temperature range and relevant supply

voltage range are guaranteed by design and characterization. Typical values at +25°C.)

Note 3: Capacitance on the IO pin could be 800pF when power is first applied. If a 5kΩ resistor is used to pull up the IO line to

VPUP 5µs after power has been applied, the parasite capacitance will not affect normal communications.

Note 4: Guaranteed by design, simulation only. Not production tested.

Note 5: Maximum value represents the internal parasite capacitance when VPUP is first applied. Once the parasite capacitance is

charged, it does not affect normal communication.

Note 6: Input load is to ground.

Note 7: The voltage on IO must be less than or equal to VILMAX whenever the master drives the line low.

Note 8: VIH is a function of the internal supply voltage.

Note 9: The reset low time (tRSTL) should be restricted to a maximum of 960µs to allow interrupt signaling. A longer duration could

mask or conceal interrupt pulses if this device is used in parallel with a DS1994.

Note 10: An additional reset or communication sequence cannot begin until the reset high time has expired.

Note 11: Presence pulse is guaranteed only after a preceding reset pulse (tRSTL).

Note 12: ε in Figure 7 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VIH. The actual

maximum duration for the master to pull the line low is tW1LMAX + tF - ε and tW0LMAX + tF - ε, respectively.

Note 13: δ in Figure 7 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input-high

threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF.

Detailed Description

The block diagram in Figure 1 shows the major function

blocks of the device. The DS1990A takes the energy it

needs to operate from the IO line, as indicated by the

parasite power block. The ROM function control unit

includes the 1-Wire interface and the logic to implement

the ROM function commands, which access 64 bits of

unique ROM.

Figure 1. Block Diagram

SIZE

See the Package Information section.

WEIGHT (DS1990A)

Ca. 2.5 grams

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Analog Devices │ 3

DS1990A

Serial Number iButton

Electrical Characteristics (continued)

iButton CAN PHYSICAL SPECIFICATION

DS1990A

PARASITE POWER

ROM

FUNCTION CONTROL

IO

64-BIT

UNIQUE ROM