Description

The SG1845N is an IC chip belonging to the SG1844/45 family of control ICs. It is designed to implement off-line fixed frequency, current-mode switching power supplies with a minimum number of external components. The current-mode architecture of this chip provides improved line regulation, improved load regulation, pulse-by-pulse current limiting, and inherent protection of the power supply output switch. It also features a bandgap reference that is trimmed to ±1% over temperature, oscillator discharge current trimmed to less than ±10%, undervoltage lockout, current-limiting circuitry, and start-up current of less than 1mA. The output of the SG1845N is optimized to drive the gate of a power MOSFET.

Specifications and features

• Optimized for off-line control
• Low start-up current (<1mA)
• Automatic feed-forward compensation
• Trimmed oscillator discharge current
• Pulse-by-pulse current limiting
• Enhanced load response characteristics
• Undervoltage lockout with 6V hysteresis (SG1844 only)
• Double pulse suppression
• High-current totem-pole output
• Internally trimmed bandgap reference
• 500kHz operation
• Undervoltage lockout SG1844 - 16 volts SG1845 - 8.4 volts
• Low shoot-through current <75mA over temperature

Application Scenarios

The SG1845N is primarily used in off-line fixed frequency, current-mode switching power supplies with a minimum number of external components. This chip is commonly found in applications requiring high-current totem-pole output, enhanced load response characteristics, and pulse-by-pulse current limiting.

Comparison

• Improved line regulation
• Improved load regulation
• Pulse-by-pulse current limiting
• Inherent protection of the power supply output switch
• Optimized to drive the gate of a power MOSFET
• Low start-up current (<1mA)
• Automatic feed-forward compensation
• Trimmed oscillator discharge current
• Enhanced load response characteristics
• Undervoltage lockout with 6V hysteresis (SG1844 only)
• Double pulse suppression
• High-current totem-pole output
• Internally trimmed bandgap reference
• 500kHz operation

• Undervoltage lockout threshold is 16 volts for SG1844 and 8.4 volts for SG1845
• Shoot-through current is low (<75mA) over temperature