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DS1482
1-Wire Level Shifter and Line Driver with Load Sensor
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FEATURES

Works with All iButtons(R) and 1-Wire(R) Devices Communicates at Regular and Overdrive 1Wire Speed (Host-Dependent) Separate Interface Power Supply to Level Shift to Non-5V Systems External Strong-Pullup Control Pin can be Used to Provide Low-On-Resistance-High Current Power Source Load Sensor to Detect when Strong-Pullup Power Delivery is no Longer Needed Power Delivery DONE Signal can be Connected to Host Interrupt Low-Cost 16-Pin SO Surface-Mount Package Operating Temperature Range: -40C to +85C
PIN ASSIGNMENT
VCCQ N.C. SPU START TXD N.C. GND N.C.
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
VCC N.C. PCTLZ DONE RXD N.C. I/O N.C.
ORDERING INFORMATION
DS1482S SO-16 DS1482S/T&R SO-16, Tape-and-Reel Contact the factory for versions with different signal polarities.
DESCRIPTION
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 (VCC) and an interface supply (VCCQ). 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 generates a control signal (PCTLZ) for an external low-impedance PMOS transistor (Figure 2) that bypasses the 1-Wire pullup resistor (RPUP) to provide power for 1-Wire devices with a high-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a high-precision comparator because it is important for the host micro to know when the high load on the 1-Wire side is no longer active.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.
iButton and 1-Wire are registered trademarks of Dallas Semiconductor.
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032103
DS1482
PIN 1 3 4 5 7 10 12 13 14 16 2, 6, 8, 9, 11, 15
NAME VCCQ SPU START TXD GND I/O RXD DONE PCTLZ VCC N.C.
FUNCTION Operating voltage for all circuitry that connects to the controlling microprocessor (TXD, RXD, START, SPU, DONE pins). This line is used to control the external strong pullup function. When SPU is low, the strong pullup (PCTLZ) is high. When SPU is high and TXD is low, PCTLZ is low. This line acts as an enable control for the DONE pin. If START is high, then DONE reflects the filtered digital output of the current-sense comparator. If START is low, then DONE is low. When TXD is low, the I/O pin is pulled resistively to VCC. When TXD is high, the 1-Wire bus is pulled to GND (for write-0, write-1, read, and reset low times). Ground Reference for VCCQ, VCC, 1-Wire 1-Wire Data This line returns the digital state of the 1-Wire bus, level-shifted to swing between VCCQ and GND. This line is high only when the buffered, filtered digital output from the current-sense comparator indicates that the downstream 1-Wire slave device is no longer sinking high current. This signal is enabled if START is high. Active-low control pin for an external low-on-resistance, high-current supply. This signal typically controls the gate of a P-channel MOSFET. This signal is low when SPU is high and TXD is low. Operating voltage for all circuitry that connects to the 1-Wire environment (I/O and PCTLZ pins). Not Connected
Figure 1. Block Diagram
LEVEL-SHIFT BOUNDARY VCCQ RPUP RXD TXD I/O VCC
GND
+
DONE START
-
Vref
PCTLZ SPU
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DS1482
Figure 2. Typical Operating Circuit
VCC = 5V RS VCCQ = 3.3V IRLMS6702 Selecting RS Assuming that the series resistance of the FET in on-condition can be neglected, the value of RS is limited as follows: RSmax = 0.0015 x VCCmin/I(standby,max) RSmin = 0.01 x VCCmax/I(active,min) Example: VCCmin = 4.5V, VCCmax = 5.5V I(standby,max) = 0.15mA I(active,min) = 12mA RSmax = 45W, RSmin = 4.58W 1-Wire NETWORK GND To maximize available power on the 1-Wire line, RS should be close to the lowest permissible value, in this example 5.1W 5%. The effect of the on-chip pullup resistor is negligible.
(21)
VCCQ
SH7622
C
(164) TxD0 (171)
VCCQ
VCC
PCTLZ
DS1482
TXD RXD SPU START DONE I/O
RxD0 (32) PTA0 (31) PTA1 (178) IRQ7
Figure 3. DS1482 Application Signals, Normal Communication
TXD
H L
I/O
H L
RXD SPU, START, DONE ALL LOW
H L
Figure 4. DS1482 Application Signals, Strong Pullup Case
TXD
H L
I/O
H L
RXD
H L
SPU
H L
PCTLZ 1 tCF DONE 4 2 3
H L
CURRENT
H L
START
H L
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DS1482
Point 1: Point 2:
Point 3: Point 4:
The 1-Wire slave device starts drawing current (internal micro or numeric processor is running). The strong pullup (SPU) must be activated before the high current phase begins. The 1-Wire slave device no longer draws current. After the deglitching time (tCF) is over, the DONE signal turns high. The START signal must be activated no later than tSD before tCF is over. Typically START is activated shortly after SPU, but not before the 1-Wire slave device has started drawing high current. As soon as the DONE signal is high, the host micro ends the strong pullup by changing SPU to low. While the DONE signal is high, the host micro changes START to low; this may occur simultaneously with the state change of SPU or later. When START changes to low, DONE becomes low.
Figure 5. Timing References TXD to I/O
TXD
tTI tTI 0.9 x VCC 0.7 x VCCQ 0.2 x VCCQ
I/O
0.1 x VCC tFIO
Figure 6. Timing References I/O to RXD
I/O
tIR tIR 0.9 x VCCQ 0.7 x VCC 0.2 x VCC
RXD
0.1 x VCCQ tF tR
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DS1482
Figure 7. Timing References SPU to PCTLZ
SPU
tSP tSP 0.9 x VCC 0.7 x VCCQ 0.2 x VCCQ
PCTLZ
0.1 x VCC tF tR
Figure 8. Timing References START to DONE
START
0.2 x VCCQ tSD 0.9 x VCCQ
DONE
0.1 x VCCQ tR tF
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DS1482
ABSOLUTE MAXIMUM RATINGS*
Voltage to GND (All Pins) -0.5V, +6.0V Combined Source/Sink Current (All Pins) 20mA Operating Temperature Range -40C to +85C Junction Temperature +150C Storage Temperature Range -55C to +125C Lead Temperature (Soldering) See IPC/JEDEC 020A ESD requirements are 15kV for the I/O pin and 4kV for all other pins. * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
ELECTRICAL CHARACTERISTICS (VCC = 4.5V to 5.5V, VCCQ = 3.0V to 3.6V; TA = -40C to +85C.)
PARAMETER SYMBOL CONDITIONS MIN Supply Current ICC Supply Current ICCQ Supply Ramp-up VCC, VCCQ rising from 0 Time (System tRCC to VCCMIN and VCCQMIN, 0.1 Requirement) respectively 1-Wire Pullup RPUP 850 Resistor INPUT PINS SPU, START, TXD 0.7 x VCCQ Input High Voltage VIH Input Low Voltage VIL Measured with either 0V Input Leakage ILP or VCCQ on the pin (Note 1) No DC load on I/O; see Delay TXD to I/O tTI Figure 5 (Note 2) I/O PIN (1-WIRE) Output Low Voltage VOL 100mA load Output High Voltage VOH No DC load Pin Leakage Current ILP (Note 3) -1 0.7 x VCC Input High Voltage VIH Input Low Voltage VIL Comparator 0.99 x VCC VREF Reference Voltage Output Fall Time tFIO 0.9 x VCC to 0.1 x VCC 45 (50pF Load) TYP MAX 150 100 UNITS A A s 1650 W V V A ns V V A V V V ns
0.2 x VCCQ
3 100 0.4 VCC +1
0.995 x VCC 0.2 x VCC 0.998 x VCC
150
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DS1482
PARAMETER SYMBOL OUTPUT PIN RXD Output-Low Voltage VOL Output-High Voltage VOH Output Rise Time tR (50pF Load) Output Fall Time tF (50pF Load) Delay I/O to RXD tIR (50pF Load) OUTPUT PIN PCTLZ Output-Low Voltage VOL Output-High Voltage VOH Output Rise Time tR (50pF Load) Output Fall Time tF (50pF Load) Delay SPU to PCTLZ tSP (50pF Load) OUTPUT PIN DONE Output-Low Voltage VOL Output-High Voltage VOH Output Rise Time tR (50pF Load) Output Fall Time tF (50pF Load) Delay I/O to DONE tCF (50pF Load) Delay START to tSD DONE (50pF Load) Note 1: Note 2:
CONDITIONS 100A load -100A load 0.1 x VCCQ to 0.9 x VCCQ 0.9 x VCCQ to 0.1 x VCCQ See Figure 6 (Note 2) 100A load -100A load 0.1 x VCC to 0.9 x VCC 0.9 x VCC to 0.1 x VCC See Figure 7 (Note 4) 100A load -100A load 0.1 x VCCQ to 0.9 x VCCQ 0.9 x VCCQ to 0.1 x VCCQ START at VCCQ (Note 5) See Figure 8
MIN
VCCQ - 0.5V
TYP
MAX 0.4 50 50 100 0.4
UNITS V V ns ns ns V V ns ns ns V V ns ns s ns
VCC - 0.5V
50 50 100 0.4
VCCQ - 0.5V
50 50 128 500 100
Note 3: Note 4: Note 5:
The input pins have a weak pulldown. For OD read- or write-1 time slots, TXD should be pulsed high for 1.28s. The window for sampling RXD begins 1.8s after TXD has turned high and ends 2.05s after TXD has turned high. RXD must be sampled inside this window. Correct sampling can be achieved with the particular recommended microcontroller Hitachi SH7622 if the peripheral module operating frequency PF is higher or equal to 22MHz. Measured either with VCC on the pin and TXD low or with 0V on the pin and TXD high. This parameter is guaranteed by design, and is not production tested. The PCTLZ signal is gated by TXD. The PCTLZ output is only low if TXD is low. Characteristic of the glitch-eating filter on the output of the load-sensing comparator, i.e., an event where the downstream 1-Wire slave device is sinking high current, ceases sinking the current for less than this amount of time, and resumes sinking the current does not generate high level on DONE; DONE goes high this amount of time after the downstream 1-Wire slave device has ceased sinking high current.
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