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| DS21T16 PRODUCT PREVIEW DS21T16 SCSI Terminator FEATURES PIN ASSIGNMENT TERMPWR1 HS-GND R1 R2 R3 R4 R5 HS-GND VREF1 GND 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 PD VREF2 HS-GND NC R9 R8 R7 R6 HS-GND TERMPWR2 * Fully SCSI compliant with SCSI-1, Fast SCSI and Ultra * Pin compatible to the DS2107AE and DS21S07AE * Provides active termination for nine signal lines * Supports TERMPWR 2.7V - 5.50V * Low dropout voltage regulator * Power-down from the bus mode isolates termination resistors * SCSI bus hot-plug compatible * Fully supports actively negated SCSI signals * Onboard thermal shutdown circuitry * 20-pin plastic TSSOP (Thin Shrink Small Outline Package) (DS21T16E) DS21T16E 20-PIN TSSOP (173 MIL) DESCRIPTION Fast SCSI and Ultra SCSI require the use of active terminations at both ends of every cable segment in a SCSI system with single-ended drivers and receivers. The DS21T16 SCSI Terminator, which is fully compliant with these standards, enables the designer to gain the benefits of active termination: greater immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T16 integrates a regulator and nine precise switched 110 ohms termination resistors into a monolithic IC. The DS21T16 can be electrically isolated from the SCSI bus without physical removal from the SCSI device. level which is fed to a buffer amplifier. The buffer produces a 2.7V level and is capable of sourcing at least 24 mA into each of the termination resistors when the signal line is low (active). When the driver for a given signal line turns off, the terminator will pull the signal line to 2.7V (quiescent state). To handle actively negated SCSI signals, the buffer can sink at least 200 mA, and VREF will move less than 60 mV. When all lines settle in the quiescent state, the regulator will consume about 2.5 mA. When the DS21T16 is put into power-down mode by bringing PD low, the power-down circuitry will turn off the transistors on each signal line. This will isolate the DS21T16 from the signal lines and effectively remove it from the circuit. The power-down pin (PD) has an internal 50K pull-up resistor. To place the DS21T16 into an active state, the PD pin should be left open circuited. When installed on disk drives or RAID system components, the DS21T16 will not affect the SCSI bus during a hot plug operation. FUNCTIONAL DESCRIPTION The DS21T16 consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1). The bandgap reference circuit produces a precise 2.55V 063098 1/6 DS21T16 To ensure proper operation, both the TERMPWR1 and TERMPWR2 pins must be connected to the SCSI bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each DS21T16 requires a 4.7 F capacitor connected between the VREF pins and ground. Figure 2 details a typical SCSI bus configuration. In an 8-bit wide SCSI bus arrangement ("A" Cable), two DS21T16s would be needed at each end of the SCSI cable in order to terminate the 18 active signal lines. In a 16-bit wide SCSI bus arrangement ("P" Cable), three DS21T16s would be needed at each end of the SCSI cable in order to terminate the 27 active signal lines. DS21T16 BLOCK DIAGRAM Figure 1 PD TERMPWR1 TERMPWR2 50K POWER DOWN CIRCUITRY 110 OHMS R1 110 OHMS R2 BANDGAP REFERENCE + 110 OHMS R3 110 OHMS R4 110 OHMS R5 110 OHMS R6 GND 110 OHMS R7 110 OHMS R8 110 OHMS R9 VREF1 VREF2 - 063098 2/6 DS21T16 TYPICAL SCSI BUS CONFIGURATION Figure 2 Termination Power Line + C2 DS21T16 TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 DS21T16 TERMPWR1 TERMPWR2 VREF1 VREF2 GND R1 R2 C1 + SCSI CABLE R8 R9 C1 + R9 SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER SCSI BUS TRANSCEIVER NOTES: 1. C1 = 4.7 F tantalum C2 = 2.2 F tantalum or 4.7 F aluminum 2. If the DS21T16 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is that recommended TERMPWR be derived from the SCSI cable, not generated locally. In this configuration, if a power failure occurs in the peripheral, it will not affect the bus. 3. A high frequency bypass capacitor (0.1 F recommended) can be added in parallel to C1 for applications using fast rise/fall time drivers. 063098 3/6 DS21T16 PIN DESCRIPTION Table 1 DS21T16E PIN 1 DS21T16S PIN 1 SYMBOL TERMPWR1 DESCRIPTION Termination Power 1. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2 F or 4.7 F. See Figure 2. Signal Termination 1. 110 ohms termination. Signal Termination 2. 110 ohms termination. Signal Termination 3. 110 ohms termination. Signal Termination 4. 110 ohms termination. Signal Termination 5. 110 ohms termination. Reference Voltage 1. Must be externally connected directly to the VREF2 pin. Must be decoupled with a 4.7 F capacitor as shown in Figure 2. Ground. Signal ground; 0.0V. Termination Power 2. Should be connected to the SCSI TERMPWR line. Must be decoupled with either a 2.2 F or 4.7 F. See Figure 2. Signal Termination 6. 110 ohms termination. Signal Termination 7. 110 ohms termination. Signal Termination 8. 110 ohms termination. Signal Termination 9. 110 ohms termination. No Connect. Do not connect any signal to this pin. Reference Voltage 2. Must be externally connected directly to the VREF1 pin. Must be decoupled with a 4.7 F capacitor as shown in Figure 2. Power Down. When tied low, the DS21T16 enters a power-down mode. Contains an internal 50K pull-up. Strap low to deactivate the DS21T16, leave open circuited to activate the DS21T16. Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electrically isolated from other circuitry. 3 4 5 6 7 9 2 3 4 5 6 7 R1 R2 R3 R4 R5 VREF1 10 11 8 9 GND TERMPWR2 13 14 15 16 17 19 10 11 12 13 14 15 R6 R7 R8 R9 NC VREF2 20 16 PD 2, 8, 12, 18 N/A HS-GND 063098 4/6 DS21T16 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -1.0V to +6.0V 0C to 70C -55C to +125C 260C for 10 seconds * 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. The Dallas Semiconductor DS21T16 is built to the highest quality standards and manufactured for long term reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing methods. However, the DS21T16 is not exposed to environmental stresses, such as burn-in, that some industrial applications require. For specific reliability information on this product, please contact the factory in Dallas at (972) 371-4448. RECOMMENDED OPERATING CONDITIONS PARAMETER TERMPWR Voltage PD Active PD Inactive SYMBOL VTP VPDA VPDI MIN 2.7 -0.3 2.0 TYP 3.3 MAX 5.50 +0.8 VTP +0.3 UNITS V V V (0C to 70C) NOTES DC CHARACTERISTICS PARAMETER TERMPWR Current Power Down Current Termination Resistance Die Thermal Shutdown Power Down Termination Capacitance Input Leakage High Input Leakage Low SYMBOL ITP ITP IPD RTERM TSD CPD IIH IIL -1.0 1.0 107.5 150 3.0 5.0 MIN TYP 2.5 100 110 MAX 250 5 150 119.5 UNITS mA mA A ohms C pF A A (0C to 70C) NOTES 1, 3 1, 4 1, 2, 5 1, 2 1, 6 1, 2, 5, 6 1, 8 1, 7 REGULATOR CHARACTERISTICS PARAMETER Output Voltage Drop Out Voltage Line Regulation Load Regulation Current Limit Sink Current SYMBOL VREF VDROP LIREG LOREG ILIM ISINK 200 MIN 2.5 TYP 2.7 0.1 1.0 1.3 950 MAX 3.0 0.2 2.0 3.0 UNITS V V % % mA mA (0C to 70C) NOTES 1, 2 3, 6 1, 4 1, 3 1 1 063098 5/6 DS21T16 NOTES: 1. 2.7V < TERMPWR < 3.3V. 2. 0.0V signal lines TERMPWR. 3. All signal lines = 0.0V. 4. All signal lines open. 5. PD = 0.0V. 6. Guaranteed by design; not production tested. 7. R1 through R9 only. 8. R1 through R9 and PD. DS21T16E SCSI TERMINATOR 20-PIN TSSOP D n c SEE DETAIL A E H A2 A A1 L B DETAIL A e1 phi G DIM A MM A1 MM A2 MM C MM L MM e1 MM B MM D MM E MM G MM H MM phi MIN - 0.05 0.75 0.09 0.50 MAX 1.10 - 1.05 0.18 0.70 0.65 BSC 0.18 6.40 0.30 6.90 4.40 NOM 0.25 REF 6.25 0 6.55 8 063098 6/6 |
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