The HIN232-HIN241 series RS-232 transmitter/receiver interface circuit meets all E1ARS-232E and V.28 specifications and is particularly suitable for applications where ±12V is not available. They need a single +5V power supply (except HIN239) and a functional on-board charge pump voltage converter that produces +10V and 5V power supply -10V power. This family of devices offers a wide variety of RS-232 transmitter/receiver combinations to suit different applications. The driver features true TTL/CMOS compatible inputs, slew rate limited output, and 300Ω off supply impedance. The receiver can handle up to ±30V and has a 3kΩ to 7kΩ input impedance. The receiver also has hysteresis, which greatly improves noise rejection.
The HIN232-HIN241 Series RS-232 Transmitter/Receiver is powered by a single +5V supply (except HIN239) with low power consumption and meets all E1ARS-232C and V.28 specifications. The circuit is divided into three parts: a charge pump, a transmitter and a receiver.
Figure 1 charge pump:
Equivalent Circuit of Charge Pump The charge pump shown in Figure 1 contains two parts: a voltage multiplier and the voltage type inverter. Each section is driven by a two-phase, internally generated clock to produce +10V and -10V. The nominal clock frequency is 16 kHz. In one of the first phase clocks, capacitor C1 is charged to VCC. In phase 2, the voltage on C1 is applied to VCC, producing a signal across C3 equal to twice VCC. In the first phase, C2 is also recorded as 2VCC, and then in the second phase, it is inverted to ground to produce a signal at both ends of C4 of -2VCC. The charge pump accepts input voltages up to 5.5V. The output multiplier portion has an output impedance (V+) of about 200 Ω, and the output impedance voltage of the inverter portion (V-) is about 450 Ω. A typical application uses a 1μF capacitor C1?C4, however, this value is not critical. Increasing the values of C1 and C2 will reduce the output impedance of the voltage multiplier and the inverter, increasing the storage capacitor, and the values of C3 and C4 reduce the ripple on the V+ and V- supplies. When the shutdown control mode (HIN236, HIN240, and HIN241) shutdown control line is set to logic "1", when the charge pump is off, V+ is pulled low to VCC type, V-type is pulled up to GND, and the supply current is reduced to Less than 10μA. The transmitter output is disabled and the receiver output is placed in a high impedance state
Figure 2 Transmitter：
The transmitter is a TTL/CMOS compatible inverter which translates the input to the RS-232 output. The input logic threshold is approximately 26% VCC or 1.3V VCC = 5V. The voltage between -5V and V- in the logic 1 input is at the output, and the result of logic 0 is between +5V and (V+-0.6V). Each emitter input has an internal 400kΩ pull-up resistor so that any unused input can be left floating and its output held in its low state. The output voltage swing meets the ±5V minimum RS-232C specification and the worst case 3kΩ minimum load for all transmitter drives: conditional impedance, VCC=4.5V, and maximum allowable operating temperature. The transmitter has an internal limiting output slew rate of less than 30V/μs. The output is a short circuit protection function that can short circuit to ground. The power-off output impedance is 300Ω minimum with ±2V applied to the output and the fifth CC=0V.
Figure 3 receiver:
Figure 4 propagation delay definition:
The receiver input accepts up to ±30V and presents the required 3kΩ to 7kΩ input impedance even when the power is off (VCC=0V). The receiver has a typical input threshold of 1.3V which is within ±3V and is referred to as the transition zone in the RS-232 connection specific cation. The receiver output is 0V to VCC. The output will be low when the input is greater than 2.4V and high as long as the input is floating or between +0.8V and -30V. The receiver features 0.5V hysteresis to improve noise rejection. The receiver enable line EN, when set to logic "1", (HIN236, HIN239, HIN240, and HIN241) disables the receiver outputs and places them in high impedance mode. When the receiver output is also placed in a high impedance state, it is in shutdown mode.