Architecture of Analog or Mixed-Mode Power IC
Integrated circuits for automotive power applications follow simple, well-known architecture solutions, which subscribe to the main application topics:
- • Non-isolated power supplies or dc/dc converters
- • Isolated power supplies
- • Motor drives
High-voltage gate drivers for High-voltage propulsion drives.
Example of Disruptive Innovation—PWM Control Chip
The PWM control integrated circuit was invented by Bob Mammano in 1975, and introduced to the market in 1976 by the Silicon General Company as SG1524. In the 1970s, PWM Control IC was developed by multiple corporations, with products like the Motorola MC3420. Texas Instruments TL454, Signetics NE5560, and Ferranti ZN1066. The solution uses a mixed-mode integrated-circuit technology with a simple (well-known today) structure. Its invention coincided with the advent of switching power supplies in the late 1970s, and satisfied a clear market need, able to add value to the customers.
The PWM IC allowed for the creation of a new market with a paradigm (vendors competing customers), the addition of a new set of customers, enabling new power supply technologies and more incremental development like current-mode ICs, cycle-by-cycle current-limiting protection, single-ended, push-pull supplies, LDOs, hot-swap, soft-switching, and so on.
Figure 13.2 provides the description of a current-controlled buck converter. An architecture for the appropriate controller is shown in Figure 13.3.
A band gap reference inside the integrated circuit provides a fixed 1.2 V reference. The reference voltage is compared with the feedback information, either current from a current sensor or voltage from a resistive divider. The resulting error
FIGURE 13.2 Current-controlled buck converter.
FIGURE 13.3 Principle schematic for the control integrated circuit.
is processed through an error amplifier, which is an operational amplifier with a passive network on the feedback path, able to correct (compensate) the dynamic response of the overall system. This passive network classifies the controller as Type I, Type II, or Type III (for details, see Chapter 9).
The output of the error amplifier represents the reference for the PWM generator. The PWM is generated with a comparison between a triangular carrier signal of high frequency (kHz) and the output of the error amplifier. The triangular signal is generated outside the integrated circuit witli a resistive-capacitive network, aiming at charging the capacitor with a delay. The linearly increasing voltage is reset when the rising slope reaches a predefined threshold. The capacitor is suddenly discharged and the linear charging starts over. This forms a triangular waveform, called a carrier, produced at a high frequency, in the range of kHz.
When the output of the error amplifier is larger than the triangular carrier, the switch is controlled in an “on” state, but otherwise stays “off’.
An auxiliary protection circuit monitors various parameters (current, voltage, temperature); if they go beyond limits of good operation, a shutdown signal is generated to block the further generation of control [PWM] pulses. The protection circuit can either wait for operator reset or work pulse-by-pulse and automatically reset at the end of each PWM sequence.
