ZHCSEZ3C May   2016  – May 2016 TRS3122E

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Characteristics
    5. 6.5  Power and Status Electrical Characteristics
    6. 6.6  Driver Electrical Characteristics
    7. 6.7  Receiver Electrical Characteristics
    8. 6.8  Driver Switching Characteristics
    9. 6.9  Receiver Switching Characteristics
    10. 6.10 Power and Status Switching Characteristics
    11. 6.11 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Charge Pump
        1. 8.3.1.1 Doubler Mode
        2. 8.3.1.2 Tripler Mode
      2. 8.3.2 Drivers
      3. 8.3.3 Receivers
      4. 8.3.4 ESD Protection
      5. 8.3.5 Auto Powerdown Plus
        1. 8.3.5.1 Automatic Powerdown
        2. 8.3.5.2 Manual Powerdown
        3. 8.3.5.3 Forced On
    4. 8.4 Device Functional Modes
      1. 8.4.1 Each Driver
      2. 8.4.2 Each Receiver
      3. 8.4.3 INVALID Status Truth Table
      4. 8.4.4 Capacitor Selection Table
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical 1.8-V Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Data-Rate and Cable Length
        2. 9.2.2.2 Capacitor Selection
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12器件和文档支持
    1. 12.1 器件支持
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 社区资源
    3. 12.3 商标
    4. 12.4 静电放电警告
    5. 12.5 Glossary
  13. 13机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

8 Detailed Description

8.1 Overview

The TRS3122E is an upgrade to standard RS232 transceivers, offering compatibility with modern system needs like 1.8-V GPIO capability, enhanced ESD & ultra low stand-by current. The majority of RS-232 transceivers with 1.8-V GPIO compatibility require a logic supply pin for the I/O translation, in addition to a minimum 3.3 V VCC for all of the other active circuitry on the chip. Unlike these transceivers, TRS3122E can operate with both VL and VCC equal to 1.8 V. When VCC= 3.0 V to 5.5 V, the charge pump will sense VCC and switch to doubler mode. C1 & C2 are the necessary flying capacitors, C3 is not needed, and the charge pump outputs V+ & V- will regulate to ~+/-5.4 V. When VCC= 1.65 V to 2.0 V, the charge pump will sense VCC and switch to tripler mode. C1, C2 & C3 are all necessary, and the charge pump outputs V+ & V- will regulate to ~+/-2.65*VCC from VCC= 1.65 V to 2.0 V.

With many modern applications expanding into products that use RS232 as a backup communication protocol, it is important for the transceiver to have efficient standby operation. In order to accommodate this, Auto Powerdown Plus has been integrated to shut-off all active circuitry, allowing TRS3122E to achieve an Ioff of 1 uA.

In order to comply with common interface system needs and environments, the RS-232 receive and transmit I/O pins comply with IEC 61000-4-2 ratings.

8.2 Functional Block Diagram

TRS3122E detail_schemv2.gif Figure 12. Schematic

8.3 Feature Description

8.3.1 Charge Pump

The internal power supply consists of a regulated auto-sensing charge pump that provides RS-232 compatible output voltages, over the 1.65 V to 2.0 V and 3.0 V to 5.5 V VCC ranges. The charge pump operates in two modes to efficiently accommodate low voltage (1.8 V) and higher voltage (3.3 V & 5.0 V) supplies.

8.3.1.1 Doubler Mode

The charge pump requires two flying capacitors (C1, C2) and reservoir capacitors (C4, C5) to generate the V+ and V- supplies of approximately ±5.4 V when VCC is greater than 3 V. When VCC is >2.9V, TRS3122E will sense the supply voltage level and switch the charge pump to a doubler. Hence, no need for a third flying capacitor. C3+ & C3- pins can be left open for proper operation. If a capacitor is placed between C3+ & C3-, the charge pump will ignore this capacitor and still behave as a doubler.

For capacitor choice recommendations, please refer to Table 1.

8.3.1.2 Tripler Mode

The charge pump requires three flying capacitors (C1, C2 & C3) and reservoir capacitors (C4, C5) to generate the V+ and V- supplies of approximately ±2.65 * VCC when VCC is greater than 1.65 V. When VCC is <2.1 V, TRS3122E will sense the supply voltage level and switch the charge pump to a tripler.

For capacitor choice recommendations, please refer to Table 1.

8.3.2 Drivers

The drivers are inverting level transmitters that convert TTL or CMOS logic levels to RS-232 levels. For VCC=3.0 V to 5.0 V, the RS-232 output voltage swing is typically ±5.4 V fully loaded and ±5 V minimum fully loaded. For Vcc = 1.8 V, the RS-232 output voltage swing is typically ±.4.7 V fully loaded and ±4.25 V minimum fully loaded.

The driver outputs are protected against indefinite short-circuits to ground without degradation in reliability. These drivers are compatible with RS-232 logic levels and all previous RS-232 versions. Unused driver inputs should be connected to GND or VCC.

8.3.3 Receivers

The receivers convert EIA/TIA-232 levels to TTL or CMOS logic output levels. Receivers have an inverting output that can be disabled by using the FORCEOFF pin. Receivers remain active when the Auto Powerdown Plus circuitry autonomously enters a low power state. See Auto Powerdown Plus for more information on the Auto Powerdown mode. If the FORCEOFF pin is manually set low, the receivers will be disabled and put into 3-state mode. In either of these powerdown modes, the device will typically consume about 0.5 uA. The truth table logic of the TRS3122E driver and receiver outputs can be found in Device Functional Modes. Since receiver input is usually from a transmission line where long cable lengths and system interference can degrade the signal, the inputs have a typical hysteresis margin of 300 mV. This ensures that the receiver is virtually immune to noisy transmission lines. Should an input be left unconnected, an internal 5kΩ pull-down resistor to ground will commit the output of the receiver to a HIGH state.

8.3.4 ESD Protection

ESD protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The bus pins (driver outputs and receiver inputs) have extra protection structures, which have been tested up to ±15 kV.

ESD protection is tested in various ways. TI uses the following standards to qualify the ESD structures designed into TRS3122E:

  • ±8 kV using IEC 61000-4-2 Contact Discharge (on RINx and DOUTx pins)
  • ±15 kV using IEC 61000-4-2 Airgap Discharge (on RINx and DOUTx pins)
  • ±15 kV using the Human Body Model (HBM) (on RINx and DOUTx pins)
  • ±2 kV using the Human Body Model (HBM) (on all pins except RINx and DOUTx pins)
  • ±0.5 kV using the Charged Device Model (CDM) (on all pins)

The IEC 61000-4-2 standard is more rigorous than HBM, resulting in lower voltage levels compared with HBM for the same level of ESD protection. Because IEC 61000-4-2 specifies a lower series resistance, the peak current is higher than HBM. The TRS3122E has passed both HBM and IEC 61000-4-2 testing.

8.3.5 Auto Powerdown Plus

Powerdown is engaged in two separate cases: automatically, when no activity has occurred for a period of time, and manually, using the FORCEOFF device pin.

8.3.5.1 Automatic Powerdown

Auto Powerdown Plus is enabled when FORCEON is set LOW and FORCEOFF is set HIGH. Using TRS3122E's integrated edge detection circuitry and timer, the device can sense when there is no activity on the driver or receiver inputs for 30 seconds. When this condition is sensed by the device, it automatically shuts the charge pump off, reducing supply current to 0.5 uA. When a valid transition is sensed on one of the driver or receiver inputs, the charge pump turns back on and TRS3122E exits powerdown. The typical time to exit powerdown is typically in 30 us, but can be as long as 150 us. As a result, the system saves power without requiring any software control. Device Functional Modes summarizes the operating modes in truth table form.

While in the low power mode with Automatic Powerdown enabled (FORCEOFF = HIGH and FORCEON = LOW), the receiver inputs are still enabled.

8.3.5.2 Manual Powerdown

The device can be manually powered down by externally setting FORCEOFF pin to low logic level. Both the drivers and receivers will be powered off. Device Functional Modes summarizes the operating modes in truth table form.

8.3.5.3 Forced On

If the FORCEOFF and FORCEON pins are both set HIGH, the device will power on with Auto Powerdown Plus disabled. Both the drivers and receiver will be active regardless of inactivity. Because powerdown is autonomous, FORCEON can be used ensure drivers are ready for new data transmission if the time since last transmission (or receive data) was more than 15 seconds. Device Functional Modes summarizes the operating modes in truth table form.

8.4 Device Functional Modes

8.4.1 Each Driver(1)

INPUTS OUTPUT DRIVER STATUS
DIN FORCEON FORCEOFF TIME ELAPSED SINCE LAST
RIN OR DIN TRANSITION		 DOUT
X X L X Z Powered off
L H H X H Normal operation with
auto-powerdown plus disabled
H H H X L
L L H <30 s H Normal operation with
auto-powerdown plus enabled
H L H <30 s L
L L H >30 s Z Powered off by
auto-powerdown plus feature
H L H >30 s Z
(1) H = high level, L = low level, X = irrelevant, Z = high impedance (off), 30s is typical inactivity time

8.4.2 Each Receiver(1)

INPUTS OUTPUTS RECEIVER STATUS
RIN FORCEOFF TIME ELAPSED SINCE LAST
RIN OR DIN TRANSITION		 ROUT
X L X Z Powered off
L H X H Normal operation with
auto-powerdown plus
disabled/enabled
H H X L
Open H X H
(1) H = high level, L = low level, X = irrelevant, Z = high impedance (off), Open = input disconnected or connected driver off

8.4.3 INVALID Status Truth Table(1)

INPUTS OUTPUT
RIN1, RIN2 FORCEON FORCEOFF TIME ELAPSED SINCE LAST
RIN OR DIN TRANSITION		 INVALID
Any L or H X X X H
All Open X X X L
(1) H = high level, L = low level, X = irrelevant, Z = high impedance (off), Open = input disconnected or connected driver off

8.4.4 Capacitor Selection Table

Table 1. Capacitor Selection

VCC = VL C1 Capacitor Value C2 Capacitor Value C3 Capacitor Value C4 Capacitor Value C5 Capacitor Value
1.65 V to 2 V(1) 100 nF
3.0 V to 3.6 V(1) 100 nF 100 nF or open 100 nF
4.5 V to 5.5 V(1) 47 nF 330 nF 100 nF or open 330 nF
3 V to 5.5 V(2) 47 nF 470 nF 100 nF or open 470 nF
(1) For optimized performance, we recommend using these configurations.
(2) For applications where the Vcc variation is larger, this configuration is acceptable.
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