BD8305MUV Rohm, BD8305MUV Datasheet - Page 4

• Manufacturer Part Number: BD8305MUV
• Description: High-effciency Step-up/down Switching Regulators
• Manufacturer: Rohm

● Description of Blocks
○
BD8305MUV
c
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1.VREF
2.UVLO
3.SCP
4.OSC
5.ERROR AMP
6.PWM COMP
7.SOFT START
8.PRE DRIVER
9. STBY_IO
10. Pch/Nch FET SW
This block generates ERROR AMP reference voltage.The reference voltage is 0.8 V.
Circuit for preventing low voltage malfunction
Prevents malfunction of the internal circuit at activation of the power supply voltage or at low power supply voltage.
Monitors VCC pin voltage to turn off all output FET and DC/DC converter output when VCC voltage is lower than 2.2 V,
and reset the timer latch of the internal SCP circuit and soft-start circuit.
Timer latch system short-circuit protection circuit
When the INV pin is the set 0.8 V or lower voltage, the internal SCP circuit starts counting.
The internal counter is in synch with OSC, the latch circuit activates after the counter counts about 8200 oscillations to
turn off DC/DC converter output (about 8.2 msec when RT =47KΩ).
To reset the latch circuit, turn off the STB pin once. Then, turn it on again or turn on the power supply voltage again.
Oscillation circuit to change frequency by external resistance of the RT pin (20 pin).
When RT = 47 kΩ, operation frequency is set at 1 MHz.
Error amplifier for detecting output signals and output PWM control signals.
The internal reference voltage is set at 0.8 V.
Voltage-pulse width converter for controlling output voltage corresponding to input voltage.
Comparing the internal SLOPE waveform with the ERROR AMP output voltage, PWM COMP controls the pulse width
and outputs to the driver.
Max Duty and Min Duty are set at the primary side and the secondary side of the inductor respectively, which are as
follows:
Circuit for preventing in-rush current at startup by bringing the output voltage of the DC/DC converter into a soft-start
Soft-start time is in synch with the internal OSC, and the output voltage of the DC/DC converter reaches the set voltage
after about 1000 oscillations (About 1 msec when RT = 47 kΩ).
CMOS inverter circuit for driving the built-in Pch/Nch FET.Dead time is provided for preventing feedthrough during
switching.The dead time is set at about 15 nsec for each individual SWs.
Voltage applied on STB pin (19 pin) to control ON/OFF of IC.
Turned ON when a voltage of 1.5 V or higher is applied and turned OFF when the terminal is open or 0 V is applied.
Incorporates approximately 400 kΩ pull-down resistance.
Built-in SW for switching the coil current of the DC/DC converter. Pch FET is about 120mΩand Nch is 100mΩ.
Since the current rating of this FET is 2A,it should be used within 1.6A in total including the DC current and ripple current
of the coil.
Primary side (Lx1)
Secondary side (Lx2)
Max Duty : 100 %,
Min Duty :
Max Duty : 100 %,
Min Duty : About 15 %
0 %
4/15
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Technical Note
2010.05 - Rev.D