DS1482

The DS1482 is a simple 1-Wire line driver with load sensor and level shifter, designed to function as an interface between a 3V host system and a 1-Wire system that runs on 5V. Two supplies are provided, a 5V supply for the 1-Wire operations (V_CC) and an interface supply (V_CCQ). The DS1482 can connect  directly to a synchronous serial port if it supports the appropriate bit rates to generate 1-Wire timing.

Figure 1 shows the DS1482 block diagram. TXD is buffered and controls an N-channel transistor, which drives the 1-Wire pin I/O low, e.g., to initiate a time slot. The logic level of the I/O pin is returned through a level-shifting buffer to the RXD pin for the host processor to read. Figure 3 shows the relationship of these signals in case of a 1-Wire read time slot.

The SPU input of DS1482 generates a control signal (PCTLZ) for an external low-impedance PMOS transistor (Figure 2) that bypasses the 1-Wire pullup resistor (R_PUP) to provide power for 1-Wire devices with ahigh-load current. PCTLZ is gated by the inverted TXD signal. This prevents a high through-current in case TXD and SPU are high at the same time.

The DS1482 contains a high-precision comparator because it is important for the host micro to know when the high load on the 1-Wire side is no longer active. As shown in Figure 4, the high current load causes a small drop of the voltage on the I/O pin. The comparator detects when the high current phase ends, and enables DONE after the deglitching time tCF is over. The START signal allows the host micro to selectively enable DONE.