introduction
The H-bridge power transistor topology is increasingly a common method of bidirerating the motor and other loads from a single power voltage. In most occasions, and monitors current delivered to the load in real time by using the information to provide feedback to the operation of a control system having a very big advantage. In most new designs, people often use pulse width modulation (PWM) method to provide an efficient variable power delivery, but will do so at both ends of the load receiving fast voltage transients, resulting in problems of complicated instruments change. Linear Technology Corporation has introduced a new high side current sense amplifier can be simplified this problem.
Measure the load current of the H-bridge
Load monitoring conventional method is a routed in series with the load detecting a small value resistor, which is capable of generating a measurable voltage drop for a representative of the load current (see FIG. 1). Difficulty here is that: when the PWM operation, the common mode voltage on the sense resistor has an objectionable voltage transients, such a high-frequency transient voltages hash impair the performance of the sense amplifier operation. Although the disorder can be filtered signal to recover useful low frequency information, but the ability to provide fast fault protection will subsequently lost. In addition, such "bridging" detection resistor configuration also can not monitor the current through the switch, resulting in a number of important failure mode is not detected or is out of control (for example: switch function failure).
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Monitoring the power supply current fed to each half-bridge is a much stronger practical methods (Figure 2). The program provides a number of benefits to simplify and improve circuit performance. The main improvement is by detecting resistor at a relatively constant common mode voltage: achieved (i.e., supply voltage) can be maintained so that PWM current waveform fidelity. Further, by separately monitoring each half-bridge power supply side, it can be easily detected and may control operation of a power failure and the load devices is shorted to ground.
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May be generated by using - PWM logic "polar Size" control function, wherein a half-bridge pulled state at 100% (depending on the drive direction or polarity). Load current (fully on) the current through the switch is equal to 100% of the delivery, without being affected by the PWM duty cycle of the other half-bridge. This allows the use of high-pressure side of the sense amplifier suitable method to achieve a simple reconstruction of load current waveforms.
Simple Solutions
LTC®6103 and LTC6104 dual-channel sense amplifier is a high pressure side H-bridge adapted to perform the monitoring function. Both devices having two current detection input channels, and provides two-way output (the LTC6103) or a single bidirectional output (LTC6104). Since the operating current for each detection channel are unidirectional manner, and therefore only the half-bridge current is monitored from the fully-on.
Since the opposite direction of the other half-bridge current pulse, so that the amplifier channel remains in a OFF state, and does not affect the read operation. This means that the output signal reflects only the half-bridge current is completely turned on, the current is controlled with the load current is equal.
With its fast (microsecond) response time, these devices provide overload detection, it is possible to emit a signal indicative of a power circuit protection device in case of failure conditions occur. Both devices are in tiny MSOP-8 package (designed to achieve a compact circuit board layout), and capable of normal operation at supply voltages up to 60V. Because of their ability to withstand the transient voltage of 70V, and thus eliminates the need for surge suppression elements required in demanding automotive applications.
LTC6103 dual output may be used alone to provide overload detection, and / or used as a differential pair to provide a bidirectional signal (sample) the analog to digital converter (ADC). FIG 3 shows a typical H-bridge circuit is designed for general application. Power device may be a complementary MOSFET, pure N-channel MOSFET, or other switching devices. When bridge driving a load (assuming the example given is an electric motor), wherein an output of the LTC6103 will rise above ground, while the other output is pulled down to the ground state is maintained, thereby forming an accurate and a bidirectional differential output is never lowered below ground common mode voltage. Output selection resistor (4.99K this example) can be adjusted to meet any requirements of the ADC source impedance.
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As an alternative, the LTC6104 output structure provides a single bidirectional signal. Output line current may be supplied to a load resistor, a current can be absorbed from a load resistor (depending on which input channels are detected current). As long as the voltage Pin 4 (V-) is at least lower than expected minimum output level 0.5V, to the negative output swing will remain linear. If the load resistance connected to a suitable reference voltage (in the example shown in FIG. 4) in the case of ground pin 4 next time, this condition can be satisfied. If the pin 4 is connected to a suitable negative supply (for example: -3V), the output resistance may be connected directly to the back, to form a true bipolar output.
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in conclusion
If you have the right amplifier, then design a H-bridge power driver's load current monitor is not a difficult task. LTC6103 and LTC6104 just to meet this need. They have dual inputs and detects the output of two different configuration options, these features reduces the complexity and reduce the printed circuit area. Technology area
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