Technical parameters of secondary side controller chip NCP4326

NCP4326 handles secondary side control, improves overall power efficiency and cross regulation of each output valve, and is suitable for a quasi-resonant flyback converter. Compared with traditional methods, NCP4326 provides good cross regulation characteristics for each independent output. Powered from the main output, this device controls two independent regulation switches and accurately adjusts the output voltage we choose. The controller also integrates a precision reference voltage and a dedicated amplifier to minimize the number of components in the feedback loop. Control is performed by one device at the end of three independent output voltages.

When the power supply is in standby mode, it also has a cross-cycle working characteristic. Finally, a dedicated shutdown terminal provides a low standby power consumption characteristic that prohibits the secondary side output, which is also a key feature of NCP4326.

1. Main Features

(1) 0% to 100% duty cycle control range.

(2) Integrated shunt regulator controls the optocoupler.

(3) Internal voltage reference 1.25V.

(4) Two independent J MOSFET drive outputs.

(5) Enable/disable control of each drive.

(g) Independent soft start.

(7) Independent cross-cycle work.

(8) Standby control terminal.

(9) Driving capability of 580/650 mA source and sink current.

(10) External synchronization terminal.

(1 1) Vcc, 5V undervoltage lock terminal.

(12) Lead-free packaging.

Mainly used for DVD, set-top box, CDR, game console and other power supplies with multiple output voltages.

The typical application circuit of NCP4326 is shown in Figure 1, and the application circuit of NCP4326 and NCP1207 combined is shown in Figure 2.

Figure 1 Typical application circuit of NCP4326

Figure 2 Application circuit of NCP4326 and NCP1207 combined

2. Pin functions of NCP4326

(1) PIN CPI: Error amplifier output 1. This terminal is the output terminal of error amplifier 1 and is used for external loop compensation.

(2) PIN FBI: Voltage feedback terminal 1. This terminal is the inverting input terminal of error amplifier 1, which is connected to the first group of auxiliary outputs through a bridge voltage divider.

(3) PIN EN2: Soft start and enable terminal or disable terminal of driver 2. This terminal enables or disables driver 2. An internal current source is charged through an external capacitor to generate a peak current for soft start limit startup. Leaving this terminal open can disable the output of driver 2, but the soft start feature is lost.

(4) PIN CP2, error amplifier output 2. This terminal is the output of error amplifier 2 and is used for external loop compensation.

(5) FB2: Voltage feedback terminal 2. This terminal is the inverting input terminal of error amplifier 2, which is connected to the second set of auxiliary outputs through a bridge voltage divider.

(6) PIN Ct; Ct terminal. Connect the timing capacitor to GND.

(7) PIN SYNC: External synchronization terminal. This terminal monitors the secondary side main winding, detects the start and end of the toff phase, and enables the other two secondary side outputs to achieve good regulation rates.

(8) PIN CPm: Shunt regulator output. This terminal is the output of the shunt regulator and is an open collector.

(9) PIN FBm: Main output voltage feedback terminal. This is the inverting input terminal of the internal error amplifier and is connected to the main output through a voltage divider.

(10) PIN STBY: Standby terminal. When this terminal is pulled up internally, it is in standby mode. When this terminal is open, the standby mode is not executed. When this terminal is pulled down, the standby mode is activated, the static current is reduced to a minimum, and the output drive is disabled.

(11) PIN DRV2: Output driver 2. This terminal is the driver terminal of power MOSFET2.

(12) PlNY Vcc terminal. This terminal is connected to the secondary side main output terminal and is powered by it.

(13) PIN DRV1: Output drive 1. This terminal is the driving terminal of power MOSFET1.

(14) PIN FLUX: Voltage mirror of magnetic flux. An RC network is connected between the positive winding and this terminal, or it can be connected to the negative output winding to generate a transformer magnetic flux mirror voltage. This magnetic flux mirror is compared with the ramp wave at the ENx terminal and is used to control the soft start duty cycle.

(15) PIN GND: IC common terminal.

(16) PIN EN1: Soft start enable terminal and disable terminal of driver 1. This terminal enables or disables driver 1. An internal power supply is charged through an external capacitor to generate a peak current that limits the start-up. Leaving this terminal open can disable the output of driver 1, but the soft start feature is lost.

The internal block circuit of NCP4326 is shown in Figure 3.

Figure 3 Internal block circuit of NCP4326