The drive chip sm7055-12 is a power switch chip with current mode PWM control mode and integrated high voltage starting circuit
And high-voltage power tube, which can realize the solution of low-cost and cost-effective switching power supply system.
The chip is applied to buck and buck-boost system schemes, supports 12V output voltage, and is conveniently applied to small household appliances
Product area. It also provides perfect protection functions such as over temperature, over-current, over-voltage and under voltage to ensure the reliability of the system.
The current ID through the high voltage MOS is divided into two parts, one of which is the chip sampling current
ã Is proportional to ID:
ID Â = GID ? IS
From the above figure: (i s I FB)? R2 ? 0.23V
Main characteristics of drive power management chip sm7055-12:
Topology support: low cost buck, buck-boost and other schemes
730v single chip integration process is adopted
85vac 265vac wide voltage input
Standby power consumption is less than 120mW@220Vac
Integrated high voltage starting circuit
Integrated high voltage power switch
60KHZ fixed switching frequency
Built in frequency buffeting technology to improve EMC performance
Current mode PWM control mode
Built in over-temperature, over-current, over-voltage, under voltage and other protection functions
Built in soft start
Built in intelligent soft drive technology (improved)
Package form: to252-2, DIP8
Application fields of sm7055 driver power management chip:
Power supply for small household appliances such as rice cookers and electric pressure cookers
Drain source breakdown voltage
Drain end off state leakage current
Source drain on resistance
Hvdd on voltage
Hvdd off voltage
Hvdd hysteresis threshold voltage
Hvdd operating current
Chip charging current
It can be seen from the above formula that if the IFB current is large, the ID current is small; If the IFB current is small, the ID current is large. When IFB
Current greater than (0.23V / r2)
When, the chip will turn off PWM, and the chip will automatically enter burst mode.
Note (1): the chip shall be welded to the PCB board with 200mm2 copper foil for heat dissipation. The thickness of the copper foil is 35um, and the copper foil is connected to the PCB board
Some GND feet.
The figure above shows a typical sm7055-12 drive power management icbuck-boost circuit, in which C1, C2 and L1 form Ï filter, which is beneficial to improve EMI characteristics
Sex; R1 resistor is surge suppression element; D1 is a rectifier diode, forming a half wave rectifier circuit.
When the switching power supply is started, the voltage on the C2 capacitor will be powered to the chip hvdd through the high voltage start MOS tube inside the chip
Capacity C3 charging, when
When the C3 capacitor voltage reaches 11.5V, the internal high voltage starts, the MOS tube is closed, and the PWM is turned on, and the system starts to work.
When the C3 capacitor voltage drops below 9V, turn off the PWM signal, and the chip will generate a reset signal to make the system
Restart, this is undervoltage protection.
Slots shall be cut between the drain pin of IC and GND and hvdd to meet the requirements of safety regulations.
The routing distance between the primary loop and the test loop shall be as thick and short as possible, so that it is easier to pass the EMC test.