Datasheet

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LTC2846

sn2846 2846fs

APPLICATIO S

DESCRIPTIO

FEATURES

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

Complete DTE or DCE Multiprotocol Serial Interface with DB-25 Connector

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Data Networking

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CSU and DSU

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Data Routers

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Software-Selectable Transceiver Supports:

RS232, RS449, EIA530, EIA530-A, V.35, V.36, X.21

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Operates from Single 3.3V Supply

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TUV Rheinland of North America Inc. Certified NET1,

NET2 and TBR2 Compliant, Report No.:

TBR2/050101/02, TBR2/051501/02

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1.2MHz Boost Switching Regulator for 3.3V to 5V

Conversion

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On-Chip Cable Termination

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Complete DTE or DCE Port with LTC2844 or LTC2845

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Small Footprint

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Available in 36-Lead SSOP (0.209 Wide) Package

The LTC

2846 is a 3-driver/3-receiver multiprotocol trans-

ceiver with on-chip cable termination. When combined with

the LTC2844 or LTC2845, this chip set forms a complete

software-selectable DTE or DCE interface port that supports

the RS232, RS449, EIA530, EIA530-A, V.35, V.36 and X.21

protocols. All necessary cable termination is provided inside

the LTC2846. The LTC2846 has a boost regulator that takes

in a 3.3V input and switches at 1.2MHz, allowing the use of

tiny, low cost capacitors and inductors 2mm or less in height.

The 5V output drives an internal charge pump that requires

only five space-saving surface mounted capacitors. The

LTC2846 is available in a 36-lead SSOP surface mount

package.

3.3V Software-Selectable

Multiprotocol Transceiver

with Termination

D2 D1

LTC2844

RTS

DTRDSR DCDCTS

R2 R1R4

LTC2846

TXDSCTETXC

RXCRXD

21424111512179314192062322513 81018 7 16

2846 TA01

SCTE B

SCTE A (113)

TXD B

TXD A (103)

RXC A (115)

RXC B

RXD A (104)

RXD B

RTS A (105)

RTS B

DTR A (108)

DTR B

CTS A (106)

CTS B

LL A (141)

SG (102)

SHIELD (101)

DB-25 CONNECTOR

TXC A (114)

DCD A (109)

DCD B

DSR A (107)

DSR B

D2D3

R1R2R3

TXC B

TTTTT

Summary of content (24 pages)

PAGE 1
LTC2846 3.3V Software-Selectable Multiprotocol Transceiver with Termination U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®2846 is a 3-driver/3-receiver multiprotocol transceiver with on-chip cable termination. When combined with the LTC2844 or LTC2845, this chip set forms a complete software-selectable DTE or DCE interface port that supports the RS232, RS449, EIA530, EIA530-A, V.35, V.36 and X.21 protocols. All necessary cable termination is provided inside the LTC2846.
PAGE 2
LTC2846 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VCC Voltage.............................................. – 0.3V to 6.5V VIN Voltage .............................................. – 0.3V to 6.5V Input Voltage Transmitters ........................... – 0.3V to (VCC + 0.3V) Receivers ............................................... – 18V to 18V Logic Pins .............................. – 0.3V to (VCC + 0.3V) Output Voltage Transmitters ................. (VEE – 0.
PAGE 3
LTC2846 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VIN = 3.3V, VSHDN = VIN, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS V– Negative Charge Pump Output Voltage V.28 Mode, No Load V.28 Mode, Full Load V.35 Mode RS530, RS530-A, X.21 Modes, Full Load fOSC Charge Pump Oscillator Frequency tr Charge Pump Rise Time ● ● ● MIN TYP – 7.5 – 5.5 – 4.5 – 9.6 – 8.
PAGE 4
LTC2846 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VIN = 3.3V, VSHDN = VIN, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.2 V 40 mV V.
PAGE 5
LTC2846 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VIN = 3.3V, VSHDN = VIN, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER V.
PAGE 6
LTC2846 U W TYPICAL PERFOR A CE CHARACTERISTICS V.11 Mode ICC vs Temperature V.35 Mode ICC vs Temperature V.28 Mode ICC vs Temperature 128.0 110 37.5 127.5 105 36.5 126.5 100 36.0 126.0 ICC (mA) ICC (mA) ICC (mA) 37.0 127.0 125.5 95 125.0 90 35.0 124.5 34.5 124.0 85 34.0 123.5 80 –40 –20 40 20 60 0 TEMPERATURE (°C) 80 100 123.0 –40 –20 40 20 0 60 TEMPERATURE (°C) 33.5 –40 – 20 100 40 1.4 35 1.
PAGE 7
LTC2846 U U U PI FU CTIO S NC (Pin 1): No Connect. PGND (Pin 2): Boost Switching Regulator Power Ground. Tie PGND to SGND. VIN (Pin 3): Input Supply Pin. Input supply to boost switching regulator. 3V ≤ VIN ≤ 3.6V. Bypass with a 10µF capacitor to ground. SHDN (Pin 4): Boost Switching Regulator Shutdown Pin. Tie to 2.4V or more to enable regulator. Ground to shut down. M2 (Pin 18): TTL Level Mode Select Input 2 with Pull-Up to VIN. See Table 1.
PAGE 8
LTC2846 W BLOCK DIAGRA BOOST SWITCHING REGULATOR PGND 2 GND SW 36 SW VIN 3 VIN FB 35 FB SHDN 4 SHDN GND 34 SGND CHARGE PUMP C1– 5 C1– C2+ 33 C2+ C1+ 6 C1+ C2– 32 C2– VDD 7 VDD VEE 31 VEE VCC 8 VCC GND 30 GND 29 D1A 50Ω S1 D1 9 D1 S2 125Ω 50Ω 28 D1B 27 D2A 50Ω S1 D2 10 D2 S2 125Ω 50Ω 26 D2B D3 11 D3 25 D3/R1 A 10k 20k 6k S3 DCE/DTE 19 10k 51.5Ω S2 S1 125Ω 51.5Ω 20k 24 D3/R1 B R1 12 R1 23 R2A 20k 6k 10k R2 13 51.5Ω S3 R2 S2 125Ω 10k 51.
PAGE 9
LTC2846 TEST CIRCUITS D RL B D VOD A RL B A VOC CL 100pF RL 100Ω CL 100pF 2846 F02 2846 F01 Figure 1. V.11 Driver DC Test Circuit IB Figure 2. V.11 Driver AC Test Circuit B R B IA VCM = ±7V A + – CL A 2(VB – VA) RIN = IB – IA 2846 F03 2846 F04 Figure 3. Input Impedance Test Circuit VOB 125Ω R Figure 4. V.11, V.
PAGE 10
LTC2846 U W ODE SELECTIO Table 1 M2 M1 M0 DCE/ D1,2 D3 DTE (Note 1) (Note 1) Mode Name D1 A D2 B A D3 B A B R1 R2 R3 R1 R2,R3 (Note 2) (Note 2) (Note 2) (Note 3) (Note 3) A B A B A VDD (Note 4) VEE (Note 5) B Not Used (Default V.11) 0 0 0 0 TTL X V.11 V.11 V.11 V.11 Z Z V.11 V.11 V.11 V.11 V.11 V.11 CMOS CMOS 9.3V –6V RS530A 0 0 1 0 TTL X V.11 V.11 V.11 V.11 Z Z V.11 V.11 V.11 V.11 V.11 V.11 CMOS CMOS 9.3V –6V RS530 0 1 0 0 TTL X V.11 V.11 V.11 V.
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LTC2846 U W W SWITCHI G TI E WAVEFOR S 3V 1.5V 1.5V D 0V t PHL VO t PLH 3V 0V A –VO SR = 6V tf –3V 3V SR = 6V tr 0V –3V tf 2846 F15 tr Figure 15. V.28 Driver Propagation Delays VIH 1.5V 1.5V A VIL t PHL VOH R VOL t PLH 1.65V 1.65V 2846 F16 Figure 16. V.28 Receiver Propagation Delays U W U U APPLICATIO S I FOR ATIO Overview Mode Selection The LTC2846 consists of a boost switching regulator, a charge pump and a 3-driver/3-receiver transceiver.
PAGE 12
LTC2846 U W U U APPLICATIO S I FOR ATIO SERIAL CONTROLLER DTE DCE LTC2846 LTC2846 SERIAL CONTROLLER TXD D1 TXD 103Ω R3 TXD SCTE D2 SCTE 103Ω R2 SCTE R1 D3 TXC R1 103Ω TXC D3 TXC RXC R2 103Ω RXC D2 RXC RXD R3 103Ω RXD D1 RXD LTC2844 LTC2844 RTS D1 RTS R3 RTS DTR D2 DTR R2 DTR D3 R1 DCD R1 DCD D3 DCD DSR R2 DSR D2 DSR CTS R3 CTS D1 CTS LL LL D4 R4 R4 LL D4 2846 F17 Figure 17.
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LTC2846 U W U U APPLICATIO S I FOR ATIO (DATA) M0 LTC2846 M1 M2 DCE/DTE CONNECTOR 15 16 18 NC 19 NC CABLE DCE/DTE M2 LTC2844 M1 M0 14 13 12 11 (DATA) 2846 F18 Figure 18. Single Port DCE V.35 Mode Selection in the Cable selected. Switching the terminations with FETs is difficult because the FETs must remain off when the signal voltage is beyond the supply voltage. Alternatively, custom cables may contain termination in the cable head or route signals to various terminations on the board.
PAGE 14
LTC2846 U W U U APPLICATIO S I FOR ATIO A' A A' LTC2844 R8 6k R5 20k R1 51.5Ω R6 10k S3 LTC2846 R8 6k R6 10k RECEIVER S1 R3 124Ω S2 R4 20k B B' C' R7 10k B' GND Figure 21. V.10 Receiver Configuration GENERATOR A RECEIVER A' B B' C C' R7 10k R4 20k GND 2846 F23 Figure 23. V.11 Receiver Configuration LOAD CABLE TERMINATION RECEIVER S3 R2 51.5Ω C' 2846 F21 BALANCED INTERCONNECTING CABLE R5 20k termination impedance to the cable as shown in Figure 231.
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LTC2846 U W U U APPLICATIO S I FOR ATIO In V.28 mode, S3 is closed inside the LTC2846/LTC2844 which connects a 6k (R8) impedance to ground in parallel with 20k (R5) plus 10k (R6) for a combined impedance of 5k as shown in Figure 25. Proper termination is only provided when the B input of the receivers is floating, since S1 of the LTC2846’s R2 and R3 receivers remains on in V.28 mode1.
PAGE 16
LTC2846 U W U U APPLICATIO S I FOR ATIO Switching Regulator The circuit as shown in Figure 29 can provide up to 480mA at 5V to drive the LTC2846’s transceiver as well as its companion chip in the DTE-DCE interface. In its shut down mode with the SHDN pin at 0V, the boost switching regulator draws less than 10µA. The switching regulator has a switch current limit of 1A. This current limit protects the switch as well as the external components connected to the switching regulator.
PAGE 17
LTC2846 U TYPICAL APPLICATIO S A port with one DB-25 connector, that can be configured for either DTE or DCE operation is shown in Figure 33. The configuration requires separate cables for proper signal routing in DTE or DCE operation. For example, in DTE mode, the TXD signal is routed to Pins 2 and 14 via the LTC2846’s Driver 1. In DCE mode, Driver 1 now routes the RXD signal to Pins 2 and 14.
PAGE 18
LTC2846 U TYPICAL APPLICATIO S + (VEE • IEE) – ND • PRT (3) Since power is drawn from the supplies of the LTC2846 (VCC, VDD and VEE) at less than 100% efficiency, the LTC2846 dissipates extra power to source PDISS(2845) and PRT : PDISS1(2846) = 125% • (VCC • ICC) + 125% • 125% • (VDD • IDD) + 125% • 143% • (VEE • IEE) – PDISS(2845) – ND • PRT = 25% • (VCC • ICC) + 56% • (VDD • IDD) + 79% • (VEE • IEE) (4) From the LTC2845 Electrical Characteristics Table, for VCC = 5V, VDD = 8V and VEE = – 5.
PAGE 19
LTC2846 U TYPICAL APPLICATIO S D1 MBR0520 L1 5.6µH 3 C6 10µF SHDN 4 7 C3 1µF 36 BOOST SWITCHING REGULATOR 5 C1 1µF VCC 5V 33 30 LTC2846 9 D1 10 SCTE R2 4.3k T D2 C5 10µF C2 1µF 31 CHARGE PUMP 8 TXD 35 32 6 VCC 5V R1 13k T + VIN 3.3V C4 3.3µF 29 2 28 14 27 24 26 11 25 15 24 12 23 17 22 9 21 3 20 16 TXD A (103) TXD B SCTE A (113) SCTE B 11 D3 12 TXC 15 16 18 19 C8 1µF RTS DTR R2 14 RXD C7 1µF R1 13 RXC T R3 T T M0 7 M1 M2 17 VIN 3.
PAGE 20
LTC2846 U TYPICAL APPLICATIO S D1 MBR0520 L1 5.6µH 3 C6 10µF SHDN 4 7 C3 1µF 36 BOOST SWITCHING REGULATOR 5 C1 1µF VCC 5V 8 LTC2846 D1 10 RXC T D2 R2 4.3k 33 30 9 RXD 35 T C5 10µF C2 1µF 32 31 CHARGE PUMP 6 VCC 5V R1 13k + VIN 3.3V C4 3.3µF 29 3 28 16 27 17 26 9 25 15 24 12 23 24 22 11 21 2 20 14 RXD A (104) RXD B RXC A (115) RXC B 11 D3 12 TXC R2 14 TXD 15 16 18 NC C7 1µF R1 13 SCTE C8 1µF 19 R3 T 7 M1 M2 17 VIN 3.
PAGE 21
LTC2846 U TYPICAL APPLICATIO S D1 MBR0520 L1 5.6µH 3 C6 10µF SHDN 4 7 C3 1µF 36 BOOST SWITCHING REGULATOR 5 C1 1µF VCC 5V 8 LTC2846 D1 10 DTE_SCTE/DCE_RXC T D2 R2 4.3k 33 30 9 DTE_TXD/DCE_RXD 35 T C5 10µF C2 1µF 32 31 CHARGE PUMP 6 VCC 5V R1 13k + VIN 3.3V C4 3.
PAGE 22
LTC2846 U TYPICAL APPLICATIO S D1 MBR0520 L1 5.6µH 36 3 C6 10µF SHDN 4 7 C3 1µF BOOST SWITCHING REGULATOR 5 C1 1µF VCC 5V 8 LTC2846 D1 10 DTE_SCTE/DCE_RXC T D2 R2 4.3k 33 30 9 DTE_TXD/DCE_RXD 35 T C5 10µF C2 1µF 32 31 CHARGE PUMP 6 VCC 5V R1 13k + VIN 3.3V C4 3.
PAGE 23
LTC2846 U TYPICAL APPLICATIO S D1 MBR0520 L1 5.6µH 3 C6 10µF SHDN 4 7 C3 1µF 36 BOOST SWITCHING REGULATOR 5 C1 1µF 8 LTC2846 D1 10 DTE_SCTE/DCE_RXC T D2 R2 4.3k 33 30 9 DTE_TXD/DCE_RXD 35 T C5 10µF C2 1µF 32 31 CHARGE PUMP 6 VCC 5V VCC 5V R1 13k + VIN 3.3V C4 3.
PAGE 24
LTC2846 U PACKAGE DESCRIPTIO G Package 36-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 12.50 – 13.10* (.492 – .516) 1.25 ±0.12 7.8 – 8.2 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 5.3 – 5.7 7.40 – 8.20 (.291 – .323) 0.42 ±0.03 0.65 BSC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 RECOMMENDED SOLDER PAD LAYOUT 5.00 – 5.60** (.197 – .221) 2.0 (.079) 0° – 8° 0.09 – 0.25 (.0035 – .010) 0.65 (.0256) BSC 0.55 – 0.95 (.022 – .037) NOTE: 1.