BD8150KVT_09 Datasheet, PDF (7/19 Pages) Rohm – 4-channel System Power Supply + Gamma Buffer Amp IC

BD8150KVT
Technical Note
●Block Description
VREF
This block outputs a highly accurate reference voltage of 2.5V and has a current capacity of over 1mA. ON/OFF control is
possible using the CTL pin.
ERRAMP
This is an error amp that amplifies and outputs the NON and INV voltage differential. The output pulse duty is determined by the
output FB voltage. When FB is 1.95V or more it is switched OFF, and when 1.45V or less the output NPN Tr is switched ON.
OSC
This block determines the RT and CT switching frequency. The triangular waveform is determined by RT and CT.
Timer latch
This is a protection circuit that detects output short-circuits (when the error amp output is 1V or less). Once activated, the
timer begins charging the SCP terminal capacitance at 7μA. When the SCP voltage is 1.8V or more, the latch is applied
and shutdown begins. Recovery can be accomplished by turning on Vcc and CTL.
PWM/driver
This is a PWM comparator that determines the duty by comparing the error amp output and the oscillator triangular
waveform in order to determine the maximum duty ratio for the DTC. It is turned to OFF when the DTC voltage is 1.95V
and turned ON at 1.45V. Use the VREF resistance division to set the DTC voltage.
UVLO
This is a protective circuit that shuts down the system when the input voltage becomes 2.5V in order to prevent IC
malfunction. A 0.1V hysteresis exists and reset is implemented once the voltage is at least 2.6V.
Soft start
Soft start is activated during startup in order to prevent DC/DC converter inrush current. The delay time depends on the pin
capacitance. The circuit is set to LOW when a protective circuit is triggered. When reset, soft start will once again operate
at startup.
DET
This is a comparator that detects whether each output voltage is output as set. When output as set, High is output to pins
DET1 to DET4. When all of the DET pins are High, the ENABLE pin is set to High.
U/D selector
This selector switches between the step-up DC/DC and step-down DC/DC. Step-down operation is performed for high
input, and step-up operation is performed for low input.
VREF17
A 1.7V reference voltage is output. This is used for the DTC setting. Perform resistance division from this voltage and set
the DTC voltage.
REG
This is the regulator output for the gamma correction setting. Providing gamma correction resistance division under this
regulator makes it possible to obtain a stable gamma correction voltage.
2-bit counter
A charge pump switching frequency is generated from the DC/DC converter frequency. This becomes 1/4 of the DC/DC
converter frequency.
DRV block (DC/DC converter)
This is a driver block that outputs the pulse between Vcc and GND. This directly drives the P-channel FET or N-channel
FET. For step-up, connect the N-channel FET, for step-down, connect the P-channel FET.
DRV (charge pump)
This driver block outputs the pulse between FB and GND. Feedback control is applied to the FB voltage to stabilize the
charge pump. The FB voltage only increases to the Reg Vcc voltage, so the Reg Vcc voltage is the maximum switching
amplitude.
Buffer Amp
This IC has a built-in 10channel buffer amp for gamma correction voltage generation. Using this amp allows generation of
a gamma correction voltage that is input to the source driver.
VCOM
A 1-channel differential input operation amp is built-in for VCOM. Using an external bipolar Tr buffer makes it possible to
generate a VCOM voltage.
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2009.07 - Rev.B