SG1844Y

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Power management integrated circuits (PMIC) are a type of high-performance integrated circuits (IC) used to measure or control the power supply provided to various electronic systems. System power management includes generation, regulation, and storage of electrical energy. PMICs are typically used to modify, regulate, or monitor the electronic power consumption of a system. A common application of PMICs is to convert AC power to DC power and regulate it. SG1844Y by Semtech is one such PMIC and performs the task of an AC/DC offline switcher.

SG1844Y is a current-mode, PWM-controlled AC/DC switcher with auto-restart. It is an auto-restart current-mode, 9.4 kHz constant-frequency, voltage-mode PWM IC for off-line applications. The IC offers under-voltage lockout protection, adjustable maximum peak current, and adjustability from 1.5 W to 8 W. It boasts a wide range of Voltage options from 3.3V to 36V and output power from 1.5W to 8W. The Ultralow dropout Voltage pin along with LED current sensivity pin provide budget oriented options. It also offers several control inputs such as Soft Start, Enable and PWM input for some exclusive functions as follows.

Soft Start: This applies a controlled voltage to the input of the switcher to smoothly bring up the voltage. Since the voltage is increased relatively slowly, the in-rush current experienced by the bypassed capacitor is minimized. This helps prevent possible component damage due to high in-rush currents.

Enable: This is a logic input that acts to control whether the switcher is enabled or disabled. A logic low enables the switcher, while a logic high disables it. This is useful if the system needs to be shut down, as it eliminates the need to cut the power to the switcher.

PWM Input: This is a digital input that allows external control of the switching frequency. It can be used to reduce the switching losses and EMI of the system by using a lower frequency. This is very useful for applications where the process requires frequent changes in the switching frequency.

The main working principle of SG1844Y is based on a trans-conductance amplifier (OCL) plus some additional circuitry to develop a control velocity of PWM signal, as shown in Figure 1. SG1844Y uses an OCL to provide the necessary control of output current, resulting in stable constant frequency at the output. This OCL is connected to a voltage sense amplifier, which senses the output voltage level. An error amplifier compares the voltage sense signal with a reference voltage to generate a signal, which is proportional to the error between the two signals. This error signal is used as the input to an oscillator, whose output is used as the PWM control signal. This PWM signal is then used to drive the power switch.

Figure 1 – SG1844Y Schematic

The IC has a positive symmetrical temperature coefficient and it sets the switching triggers at the appropriate levels. Because of the symmetrical design, the IC will always maintain a certain output voltage regardless of the ambient temperature. This feature helps ensure that the circuit does not become unstable due to temperature variations. The PWM control signal is also affected by the temperature, which ensures that the output remains regulated even as the temperature increases.

SG1844Y can be used in a variety of applications, including AC/DC adapters, LED lighting systems, battery charger systems, DC motors, and industrial power conversion systems. In addition, it is also suitable for applications requiring high current demands and low cost. SG1844Y is capable of delivering up to 10 A of output current while maintaining a high level of efficiency.

In conclusion, the SG1844Y is an ideal solution for a wide range of AC/DC offline switcher applications. It offers a wide input voltage range and multiple control inputs for a variety of functions. The built-in symmetrical temperature coefficient helps ensure the output remains stable even under highly varying temperatures. With its high output current capability and its low cost, the SG1844Y is the ideal choice for any application requiring AC/DC conversion.

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