BD9745EKN Datasheet, PDF (14/22 Pages) Rohm – Silicon Monolithic Integrated Circuit

○ BLOCK DESCRIPTION
1. REGA
This is an internal regulator that generates a 2.5V regulated output voltage.
REGA supplies power for all the remaining circuit blocks.
The output voltage can be supplied to external devices from VREGA (30pin).
To prevent any oscillations at the output, a 1μF external capacitor is recommended.
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2． Short Circuit Protect, Timer Latch
When Error Amp’s output of CH1,5～7 voltages rise beyond 2.2 V, or INV pin voltage of CH2,3,4 fall under
80% of reference, the timer circuit is activated. This will charge up the capacitor connected to SCP (32pin) by
approximately 4μA current.
When the voltage reaches 1.0 V, the latch circuit is activated. While this protection circuit is activated, the entire
channel’s output is turned OFF.
In order to reset the latch circuit, two methods can be used: 1) disable the STB pin before enabling it.
2) Removing or refreshing the power supply voltage.
3． U.V.L.O
This circuit protects the IC from a transient surge at power-on or a momentary drop of the power supply
voltage. Under voltage lockout is activated when the VCC pin voltage falls below 2.4V.
During activation, the output drive pins for all Channels is turned OFF.
4． VOLTAGE REFERENCE (VREF)
The reference voltage circuit for CH5 generates a 1.0V output voltage. The reference voltage can be supplied
from VREF (34pin).
This reference voltage is used to set the output voltage of CH5. When STB5 is enable, the reference is ramping
to 1V. Inverting voltage of CH5 is following this reference.
To prevent any oscillations at the output, a 1μF external capacitor is recommended.
5．OSC
The BD9745EKN include a triangular waveform oscillator for voltage-mode PWM controllers, and slope
oscillator for current-mode PWM controllers.
To set the oscillator frequency, connect a timing resistor to the RT (29 pin).
When the resistor is 62kΩ, it is set 1.2MHz(CH1～4), 600kHz(CH5～7).
REV. D