SCES582H July   2004  – April 2015 SN74AVCH2T45

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Pin Configurations and Functions
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics
    6. 7.6  Switching Characteristics: VCCA = 1.2 V
    7. 7.7  Switching Characteristics: VCCA = 1.5 V
    8. 7.8  Switching Characteristics: VCCA = 1.8 V
    9. 7.9  Switching Characteristics: VCCA = 2.5 V
    10. 7.10 Switching Characteristics: VCCA = 3.3 V
    11. 7.11 Operating Characteristics
    12. 7.12 Typical Characteristics
      1. 7.12.1 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 1.8 V
      2. 7.12.2 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 2.5 V
      3. 7.12.3 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 3.3 V
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 VCC Isolation
      2. 9.3.2 2-Rail Design
      3. 9.3.3 IO Ports are 4.6 V Tolerant
      4. 9.3.4 Partial Power Down Mode
      5. 9.3.5 Bus Hold on Data Inputs
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 Unidirectional Logic Level-Shifting Application
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Bidirectional Logic Level-Shifting Application
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
          1. 10.2.2.2.1 Enable Times
        3. 10.2.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)
  • DCU|8
  • YZP|8
  • DCT|8
散热焊盘机械数据 (封装 | 引脚)
订购信息

7 Specifications

7.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)
MIN MAX UNIT
VCCA
VCCB		 Supply voltage –0.5 4.6 V
VI Input voltage(2) I/O ports (A port) –0.5 4.6 V
I/O ports (B port) –0.5 4.6
Control inputs –0.5 4.6
VO Voltage range applied to any output
in the high-impedance or power-off state(2)		 A port –0.5 4.6 V
B port –0.5 4.6
VO Voltage range applied to any output in the high or low state(2)(3) A port –0.5 VCCA + 0.5 V
B port –0.5 VCCB + 0.5
IIK Input clamp current VI < 0 –50 mA
IOK Output clamp current VO < 0 –50 mA
IO Continuous output current ±50 mA
Continuous current through VCCA, VCCB, or GND ±100 mA
TJ Junction temperature –40 150 °C
Tstg Storage temperature –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) The input voltage and output negative-voltage ratings may be exceeded if the input and output current ratings are observed.
(3) The output positive-voltage rating may be exceeded up to 4.6 V maximum if the output current rating is observed.

7.2 ESD Ratings

VALUE UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±8000 V
Charged-device model (CDM), per JEDEC specification JESD22-C101(2) ±1000
Machine Model (MM), Per JEDEC specification JESD22-A115-A ±200
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

7.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)(3)(4)(5)
VCCI(1) VCCO(2) MIN NOM MAX UNIT
VCCA Supply voltage 1.2 3.6 V
VCCB Supply voltage 1.2 3.6 V
VIH High-level
input voltage		 Data inputs(4) 1.2 V to 1.95 V VCCI(1) × 0.65 V
1.95 V to 2.7 V 1.6
2.7 V to 3.6 V 2
VIL Low-level
input voltage		 Data inputs(4) 1.2 V to 1.95 V VCCI(1) × 0.35 V
1.95 V to 2.7 V 0.7
2.7 V to 3.6 V 0.8
VIH High-level
input voltage		 DIR
(referenced to VCCA)(5)		 1.2 V to 1.95 V VCCA × 0.65 V
1.95 V to 2.7 V 1.6
2.7 V to 3.6 V 2
VIL Low-level
input voltage		 DIR
(referenced to VCCA)(5)		 1.2 V to 1.95 V VCCA × 0.35 V
1.95 V to 2.7 V 0.7
2.7 V to 3.6 V 0.8
VI Input voltage 0 3.6 V
VO Output voltage Active state 0 VCCO(2) V
3-state 0 3.6
IOH High-level output current 1.2 V –3 mA
1.4 V to 1.6 V –6
1.65 V to 1.95 V –8
2.3 V to 2.7 V –9
3 V to 3.6 V –12
IOL Low-level output current 1.2 V 3 mA
1.4 V to 1.6 V 6
1.65 V to 1.95 V 8
2.3 V to 2.7 V 9
3 V to 3.6 V 12
Δt/Δv Input transition rise or fall rate 5 ns/V
TA Operating free-air temperature –40 85 °C
(1) VCCI is the voltage associated with the input port supply VCCA or VCCB.
(2) VCCO is the voltage associated with the output port supply VCCA or VCCB.
(3) All unused data inputs of the device must be held at VCCI or GND to ensure proper device operation. Refer to the TI application report, Implications of Slow or Floating CMOS Inputs, SCBA004.
(4) For VCCI values not specified in the data sheet, VIH min = VCCI × 0.7 V, VIL max = VCCI × 0.3 V.
(5) For VCCI values not specified in the data sheet, VIH min = VCCA × 0.7 V, VIL max = VCCA × 0.3 V.

7.4 Thermal Information

THERMAL METRIC(1) SN74AVCH2T45 UNIT
DCT (SSOP) DCU (VSSOP) YZP (DSBGA)
8 PINS 8 PINS 8 PINS
RθJA Junction-to-ambient thermal resistance 194.4 199.3 105.8 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 124.7 76.2 1.6
RθJB Junction-to-board thermal resistance 106.8 80.6 10.8
ψJT Junction-to-top characterization parameter 49.8 7.1 3.1
ψJB Junction-to-board characterization parameter 105.8 80.1 10.8
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

7.5 Electrical Characteristics

over recommended operating free-air temperature range (unless otherwise noted)(5)(6)
PARAMETER TEST CONDITIONS VCCA VCCB TA = 25°C –40°C to 85°C UNIT
MIN TYP MAX MIN TYP MAX
VOH(7) IOH = –100 μA VI = VIH 1.2 V to 3.6 V 1.2 V to 3.6 V VCCO  – 0.2 V
IOH = –3 mA 1.2 V 1.2 V 0.95
IOH = –6 mA 1.4 V 1.4 V 1.05
IOH = –8 mA 1.65 V 1.65 V 1.2
IOH = –9 mA 2.3 V 2.3 V 1.75
IOH = –12 mA 3 V 3 V 2.3
VOL(7) IOL = 100 μA VI = VIL 1.2 V to 3.6 V 1.2 V to 3.6 V 0.2 V
IOL = 3 mA 1.2 V 1.2 V 0.15
IOL = 6 mA 1.4 V 1.4 V 0.35
IOL = 8 mA 1.65 V 1.65 V 0.45
IOL = 9 mA 2.3 V 2.3 V 0.55
IOL = 12 mA 3 V 3 V 0.7
II(7) DIR input VI = VCCA or GND 1.2 V to 3.6 V 1.2 V to 3.6 V ±0.025 ±0.25 ±1 μA
IBHL(1) VI = 0.42 V 1.2 V 1.2 V 25 μA
VI = 0.49 V 1.4 V 1.4 V 15
VI = 0.58 V 1.65 V 1.65 V 25
VI = 0.7 V 2.3 V 2.3 V 45
VI = 0.8 V 3.3 V 3.3 V 100
IBHH(2) VI = 0.78 V 1.2 V 1.2 V –25 μA
VI = 0.91 V 1.4 V 1.4 V –15
VI = 1.07 V 1.65 V 1.65 V –25
VI = 1.6 V 2.3 V 2.3 V –45
VI = 2 V 3.3 V 3.3 V –100
IBHLO(3) VI = 0 to VCC 1.2 V 1.2 V 50 μA
1.6 V 1.6 V 125
1.95 V 1.95 V 200
2.7 V 2.7 V 300
3.6 V 3.6 V 500
IBHHO(4) VI = 0 to VCC 1.2 V 1.2 V –50 μA
1.6 V 1.6 V –125
1.95 V 1.95 V –200
2.7 V 2.7 V –300
3.6 V 3.6 V –500
Ioff(8) A port VI or VO = 0 to 3.6 V 0 V 0 V to 3.6 V ±0.1 ±1 ±5 μA
B port 0 V to 3.6 V 0 V ±0.1 ±1 ±5
IOZ(8) B port VO = VCCO or GND,
VI = VCCI or GND		 0 V 3.6 V ±0.5 ±2.5 ±5
A port 3.6 V 0 V ±0.5 ±2.5 ±5 μA
ICCA(8) VI = VCCI or GND, IO = 0 1.2 V to 3.6 V 1.2 V to 3.6 V 10 μA
0 V 3.6 V –2
3.6 V 0 V 10
ICCB(8) VI = VCCI or GND, IO = 0 1.2 V to 3.6 V 1.2 V to 3.6 V 10 μA
0 V 3.6 V 10
3.6 V 0 V –2
ICCA + ICCB VI = VCCI or GND, IO = 0 1.2 V to 3.6 V 1.2 V to 3.6 V 20 μA
Ci Control
inputs		 VI = 3.3 V or GND 3.3 V 3.3 V 2.5 pF
Cio A or B port VI = 3.3 V or GND 3.3 V 3.3 V 6 pF
(1) The bus-hold circuit can sink at least the minimum low sustaining current at VIL maximum. IBHL should be measured after lowering VIN to GND and then raising it to VIL maximum.
(2) The bus-hold circuit can source at least the minimum high sustaining current at VIH mininum. IBHH should be measured after raising VIN to VCC and then lowering it to VIH minimum.
(3) An external driver must source at least IBHLO to switch this node from low to high.
(4) An external driver must sink at least IBHHO to switch this node from high to low.
(5) VCCO is the voltage associated with the output port supply VCCA or VCCB.
(6) VCCI is the voltage associated with the input port supply VCCA or VCCB.
(7) VOH: Output High Voltage; VOL: Output Low Voltage; II: Control Input Current.
(8) Ioff: Partial Power Down Output current; IOZ: Hi-Z Output Current; ICCA: Supply A Current; ICCB: Supply B Current.

7.6 Switching Characteristics: VCCA = 1.2 V

over recommended operating free-air temperature range, VCCA = 1.2 V (see Figure 7)
PARAMETER FROM
(INPUT)		 TO
(OUTPUT)		 VCCB = 1.2 V VCCB = 1.5 V VCCB = 1.8 V VCCB = 2.5 V VCCB = 3.3 V UNIT
TYP TYP TYP TYP TYP
tPLH(2) A B 3.1 2.6 2.4 2.2 2.2 ns
tPHL(2) 3.1 2.6 2.4 2.2 2.2
tPLH(2) B A 3.4 3.1 3 2.9 2.9 ns
tPHL(2) 3.4 3.1 3 2.9 2.9
tPHZ(2) DIR A 5.2 5.2 5.1 5 4.8 ns
tPLZ(2) 5.2 5.2 5.1 5 4.8
tPHZ(2) DIR B 5 4 3.8 2.8 3.2 ns
tPLZ(2) 5 4 3.8 2.8 3.2
tPZH(2)(1) DIR A 8.4 7.1 6.8 5.7 6.1 ns
tPZL(2)(1) 8.4 7.1 6.8 5.7 6.1
tPZH(2)(1) DIR B 8.3 7.8 7.5 7.2 7 ns
tPZL(2)(1) 8.3 7.8 7.5 7.2 7
(1) The enable time is a calculated value derived using the formula shown in the Enable Times section.
(2) tPLH: Low-to-high Propagation Delay; tPHL: High-to-Low Propagation Delay; tPHZ: High-to-Hi-Z Propagation Delay; tPLZ: Low-to-Hi-Z Propagation Delay; tPZH: Hi-Z-to-High Propagation Delay; tPZL: Hi-Z-to-Low Propagation Delay

7.7 Switching Characteristics: VCCA = 1.5 V

over recommended operating free-air temperature range, VCCA = 1.5 V ± 0.1 V (see Figure 7)
PARAMETER FROM
(INPUT)		 TO
(OUTPUT)		 VCCB = 1.2 V VCCB = 1.5 V
± 0.1 V		 VCCB = 1.8 V
± 0.15 V		 VCCB = 2.5 V
± 0.2 V		 VCCB = 3.3 V
± 0.3 V		 UNIT
TYP MIN MAX MIN MAX MIN MAX MIN MAX
tPLH(2) A B 2.8 0.7 5.4 0.5 4.6 0.4 3.7 0.3 3.5 ns
tPHL(2) 2.8 0.7 5.4 0.5 4.6 0.4 3.7 0.3 3.5
tPLH(2) B A 2.7 0.8 5.4 0.7 5.2 0.6 4.9 0.5 4.7 ns
tPHL(2) 2.7 0.8 5.4 0.7 5.2 0.6 4.9 0.5 4.7
tPHZ(2) DIR A 3.9 1.3 8.5 1.3 7.8 1.1 7.7 1.4 7.6 ns
tPLZ(2) 3.9 1.3 8.5 1.3 7.8 1.1 7.7 1.4 7.6
tPHZ(2) DIR B 4.7 1.1 7 1.4 6.9 1.2 6.9 1.7 7.1 ns
tPLZ(2) 4.7 1.1 7 1.4 6.9 1.2 6.9 1.7 7.1
tPZH(2)(1) DIR A 7.4 12.4 12.1 11.8 11.8 ns
tPZL(2)(1) 7.4 12.4 12.1 11.8 11.8
tPZH(2)(1) DIR B 6.7 13.9 12.4 11.4 11.1 ns
tPZL(2)(1) 6.7 13.9 12.4 11.4 11.1
(1) The enable time is a calculated value derived using the formula shown in the Enable Times section.
(2) tPLH: Low-to-high Propagation Delay; tPHL: High-to-Low Propagation Delay; tPHZ: High-to-Hi-Z Propagation Delay; tPLZ: Low-to-Hi-Z Propagation Delay; tPZH: Hi-Z-to-High Propagation Delay; tPZL: Hi-Z-to-Low Propagation Delay

7.8 Switching Characteristics: VCCA = 1.8 V

over recommended operating free-air temperature range, VCCA = 1.8 V ± 0.15 V (see Figure 7)
PARAMETER FROM
(INPUT)		 TO
(OUTPUT)		 VCCB = 1.2 V VCCB = 1.5 V
± 0.1 V		 VCCB = 1.8 V
± 0.15 V		 VCCB = 2.5 V
± 0.2 V		 VCCB = 3.3 V
± 0.3 V		 UNIT
TYP MIN MAX MIN MAX MIN MAX MIN MAX
tPLH(2) A B 2.7 0.5 5.2 0.4 4.3 0.2 3.4 0.2 3.1 ns
tPHL(2) 2.7 0.5 5.2 0.4 4.3 0.2 3.4 0.2 3.1
tPLH(2) B A 2.4 0.7 4.7 0.5 4.4 0.5 4 0.4 3.8 ns
tPHL(2) 2.4 0.7 4.7 0.5 4.4 0.5 4 0.4 3.8
tPHZ(2) DIR A 3.7 1.3 8.1 0.7 6.9 1.4 5.3 1.1 5.2 ns
tPLZ(2) 3.7 1.3 8.1 0.7 6.9 1.4 5.3 1.1 5.2
tPHZ(2) DIR B 4.4 1.3 5.8 1.3 5.9 0.8 5.7 1.5 5.9 ns
tPLZ(2) 4.4 1.3 5.8 1.3 5.9 0.8 5.7 1.5 5.9
tPZH(2)(1) DIR A 6.8 10.5 10.3 9.7 9.7 ns
tPZL(2)(1) 6.8 10.5 10.3 9.7 9.7
tPZH(2)(1) DIR B 6.4 13.3 11.2 8.7 8.3 ns
tPZL(2)(1) 6.4 13.3 11.2 8.7 8.3
(1) The enable time is a calculated value derived using the formula shown in the Enable Times section.
(2) tPLH: Low-to-high Propagation Delay; tPHL: High-to-Low Propagation Delay; tPHZ: High-to-Hi-Z Propagation Delay; tPLZ: Low-to-Hi-Z Propagation Delay; tPZH: Hi-Z-to-High Propagation Delay; tPZL: Hi-Z-to-Low Propagation Delay

7.9 Switching Characteristics: VCCA = 2.5 V

over recommended operating free-air temperature range, VCCA = 2.5 V ± 0.2 V (see Figure 7)
PARAMETER FROM
(INPUT)		 TO
(OUTPUT)		 VCCB = 1.2 V VCCB = 1.5 V
± 0.1 V		 VCCB = 1.8 V
± 0.15 V		 VCCB = 2.5 V
± 0.2 V		 VCCB = 3.3 V
± 0.3 V		 UNIT
TYP MIN MAX MIN MAX MIN MAX MIN MAX
tPLH(2) A B 2.6 0.4 4.9 0.2 4 0.2 3 0.2 2.6 ns
tPHL(2) 2.6 0.4 4.9 0.2 4 0.2 3 0.2 2.6
tPLH(2) B A 2.1 0.6 3.8 0.5 3.4 0.4 3 0.3 2.8 ns
tPHL(2) 2.1 0.6 3.8 0.5 3.4 0.4 3 0.3 2.8
tPHZ(2) DIR A 2.4 0.7 7.9 0.8 6.4 0.8 5 0.5 4.3 ns
tPLZ(2) 2.4 0.7 7.9 0.8 6.4 0.8 5 0.5 4.3
tPHZ(2) DIR B 3.8 1 4.3 0.6 4.3 0.5 4.2 1.1 4.1 ns
tPLZ(2) 3.8 1 4.3 0.6 4.3 0.5 4.2 1.1 4.1
tPZH(2)(1) DIR A 5.9 8.5 7.7 7.2 6.9 ns
tPZL(2)(1) 5.9 8.5 7.7 7.2 6.9
tPZH(2)(1) DIR B 5 12.8 10.4 8 6.9 ns
tPZL(2)(1) 5 12.8 10.4 8 6.9
(1) The enable time is a calculated value derived using the formula shown in the Enable Times section.
(2) tPLH: Low-to-high Propagation Delay; tPHL: High-to-Low Propagation Delay; tPHZ: High-to-Hi-Z Propagation Delay; tPLZ: Low-to-Hi-Z Propagation Delay; tPZH: Hi-Z-to-High Propagation Delay; tPZL: Hi-Z-to-Low Propagation Delay

7.10 Switching Characteristics: VCCA = 3.3 V

over recommended operating free-air temperature range, VCCA = 3.3 V ± 0.3 V (see Figure 7)
PARAMETER FROM
(INPUT)		 TO
(OUTPUT)		 VCCB = 1.2 V VCCB = 1.5 V
± 0.1 V		 VCCB = 1.8 V
± 0.15 V		 VCCB = 2.5 V
± 0.2 V		 VCCB = 3.3 V
± 0.3 V		 UNIT
TYP MIN MAX MIN MAX MIN MAX MIN MAX
tPLH(2) A B 2.5 0.3 4.7 0.2 3.8 0.2 2.8 0.2 2.4 ns
tPHL(2) 2.5 0.3 4.7 0.2 3.8 0.2 2.8 0.2 2.4
tPLH(2) B A 2.1 0.6 3.6 0.4 3.1 0.3 2.6 0.3 2.4 ns
tPHL(2) 2.1 0.6 3.6 0.4 3.1 0.3 2.6 0.3 2.4
tPHZ(2) DIR A 2.9 1.1 8 1 6.5 1.3 4.7 1.2 4 ns
tPLZ(2) 2.9 1.1 8 1 6.5 1.3 4.7 1.2 4
tPHZ(2) DIR B 3.4 0.5 6.6 0.3 5.6 0.3 4.6 1.1 4.2 ns
tPLZ(2) 3.4 0.5 6.6 0.3 5.6 0.3 4.6 1.1 4.2
tPZH(2)(1) DIR A 5.5 10.2 8.7 7.2 6.6 ns
tPZL(2)(1) 5.5 10.2 8.7 7.2 6.6
tPZH(2)(1) DIR B 5.4 12.7 10.3 7.5 6.4 ns
tPZL(2)(1) 5.4 12.7 10.3 7.5 6.4
(1) The enable time is a calculated value derived using the formula shown in the Enable Times section.
(2) tPLH: Low-to-high Propagation Delay; tPHL: High-to-Low Propagation Delay; tPHZ: High-to-Hi-Z Propagation Delay; tPLZ: Low-to-Hi-Z Propagation Delay; tPZH: Hi-Z-to-High Propagation Delay; tPZL: Hi-Z-to-Low Propagation Delay

7.11 Operating Characteristics

TA = 25°C
PARAMETER TEST
CONDITIONS		 VCCA =
VCCB = 1.2 V		 VCCA =
VCCB = 1.5 V		 VCCA =
VCCB = 1.8 V		 VCCA =
VCCB = 2.5 V		 VCCA =
VCCB = 3.3 V		 UNIT
TYP TYP TYP TYP TYP
CpdA(1) A-port input,
B-port output		 CL = 0,
f = 10 MHz,
tr(2) = tf(2) = 1 ns		 3 3 3 3 4 pF
B-port input,
A-port output		 13 13 14 15 15
CpdB(1) A-port input,
B-port output		 CL = 0,
f = 10 MHz,
tr(2) = tf(2) = 1 ns		 13 13 14 15 15 pF
B-port input,
A-port output		 3 3 3 3 4
(1) Power dissipation capacitance per transceiver
(2) tr: Rise time; tf: Fall time

7.12 Typical Characteristics

7.12.1 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 1.8 V

SN74AVCH2T45 typ5_ces582.gif
Figure 1. Typical A-to-B Propagation Delay, Low to High
SN74AVCH2T45 typ6_ces582.gif
Figure 2. Typical A-to-B Propagation Delay, High to Low

7.12.2 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 2.5 V

SN74AVCH2T45 typ7_ces582.gif
Figure 3. Typical A-to-B Propagation Delay, Low to High
SN74AVCH2T45 typ8_ces582.gif
Figure 4. Typical A-to-B Propagation Delay, High to Low

7.12.3 Typical Propagation Delay (A to B) vs Load Capacitance, TA = 25°C, VCCA = 3.3 V

SN74AVCH2T45 typ9_ces582.gif
Figure 5. Typical A-to-B Propagation Delay, Low to High
SN74AVCH2T45 typ10_ces582.gif
Figure 6. Typical A-to-B Propagation Delay, High to Low