Datasheet

DS1990A
Serial Number i
Button
_______________________________________________________________________________________ 3
Note 8: The voltage on IO must be less than or equal to V
ILMAX
whenever the master drives the line low.
Note 9: V
IH
is a function of the internal supply voltage.
Note 10: 30nC per 72 time slots at 5.0V pullup voltage with a 5kΩ pullup resistor and t
SLOT
≤ 120µs.
Note 11: The reset low time (t
RSTL
) 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 12: An additional reset or communication sequence cannot begin until the reset high time has expired.
Note 13: Presence pulse is guaranteed only after a preceding reset pulse (t
RSTL
).
Note 14: ε in Figure 7 represents the time required for the pullup circuitry to pull the voltage on IO up from V
IL
to V
IH
. The actual
maximum duration for the master to pull the line low is t
W1LMAX
+ t
F
- ε and t
W0LMAX
+ t
F
- ε, respectively.
Note 15: δ in Figure 7 represents the time required for the pullup circuitry to pull the voltage on IO up from V
IL
to the input-high
threshold of the bus master. The actual maximum duration for the master to pull the line low is t
RLMAX
+ t
F
.
iButton CAN PHYSICAL SPECIFICATION
SIZE See the Package Information section.
WEIGHT (DS1990A) Ca. 2.5 grams
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
lasered ROM.
DS1990A
PARASITE POWER
ROM
FUNCTION CONTROL
IO
64-BIT
LASERED ROM
Figure 1. Block Diagram