bd9862muv ROHM Co. Ltd., bd9862muv Datasheet - Page 7

• Manufacturer Part Number: bd9862muv
• Description: 5v Input Multi-channel System Power Supply Ic
• Manufacturer: ROHM Co. Ltd.

●System Description
●Block functional descriptions
© 2010 ROHM Co., Ltd. All rights reserved.
BD9862MUV
www.rohm.com
BD9862MUV is a 3ch system power supply optimized for TFT liquid crystal displays.
Features of each channel are explained as follows
○CH1
○CH2
○CH3
・Error amplifier block
・PWM(Pulse Width Modulation)Convertor block
・PWM/PFM Control Block
・LDO Block
・Start-up Charge Pump Block
・OSC Block
・VREF Block
・UVLO Block
・Soft Start Block
・Short-circuit protection of timer latch (SCP) block
・Thermal shutdown (TSD) block
This is a voltage mode switching regulator with a built-in high voltage-resistant output FET. Capable of high-speed operation
at the maximum switching frequency of 1.4MHz, and compatible with a high step-up ratio with Max Duty of 90%(typ.).
It’s a PWM/PFM automatic switching control with a variable-voltage adding charge pump. Due to intermittent switching at
the time of PFM mode, the switching loss is reduced, so high efficiency is realized even in light load conditions. Moreover,
it is capable of operating at the maximum switching frequency of 700KHz because of a built-in high voltage resistant,
high-speed FET driver. In addition, it is equipped with an On Duty prediction function, so the output voltage ripple is
lowered considerably even at the time of PFM operation.Due to the built-in output discharge resistor (1kΩ typ.) and FET
phase compensation circuit, it can operate with two capacitors and two resistors.
It includes a PWM/PFM automatic switching control, variable-voltage reversing charge pump controller. The control
method is the same as CH2.
Detects the output voltage with INV terminal (NON3 terminal in case of CH3), amplifies the error between it and standard
voltage, and outputs from the FB terminal. The accuracy is ±1%(1.5% in case of CH2 & CH3).
The PWM convertor inputs the error detected by the error amplifier and outputs the PWM signal by comparing with a
saw-tooth wave.
Due to the input of the PWM terminal, this block switches the CH2 & CH3 between the fixed PWM mode and the automatic
switching mode of PFM(Pulse Frequency Modulation)/PWM. At the time of PFM mode, the efficiency under a light load is
raised by controlling and making the lowest On Duty of PWM signal to be 7%(typ.) and reducing the number of switching times.
This is a power supply to operate the internal circuit. In addition, it can be used as input of VIN2B. The output voltage is
3.5V(typ.), and the maximum load is 10mA. Moreover, due to a built-in UVLO, the release voltage is 2.5V(typ) and the
protective voltage is 2.4V(typ).
If REGOUT is ≦2.5V(typ.), then the ring oscillator, which operates at 500kHz or so, is started and the double charge
pump is operated. The clock pulse is controlled in such a way that the output voltage of this charge pump becomes
4.2V(typ.). Moreover, if REGOUT becomes more than 2.5V(typ.) (i.e. REGOUT＞2.5V(typ.)), then the clock is supplied
from the main OSC that creates a saw tooth wave. If the input voltage is usually more than 4.5V, then it is possible to
bypass the start-up circuit. (refer to the application example)
It generates a saw-tooth wave and inputs it into the PWM comparator. It is possible to change the oscillating frequency by
means of the resistor RT. Due to RRT=120kΩ, the CH1 operates at 1MHz(typ.). The double charge pump, CH2 and CH3
operate at 1/2 of CH1 frequency.
Generate the constant voltage that is standard inside the IC.
Performs the under voltage lockout by detecting the VBAT voltage with the UVLOSET terminal. The UVLO voltage can be
set by an external resistor.
Due to sweep-starting of the standard voltage of the error amplifier at the time of start-up, the excess input current & output
voltage is reduced. Moreover, only at the time of soft start, the CH2 is regarded as the resistance value of 150Ωtyp
between VIN2B & C2P and the CH3 is regarded as the resistance value of 60Ωtyp between VIN3 & C3P therefore the
input current is limited.
Monitors the INV1 terminal and the error amplifier outputs of CH2 & CH3, and turns off the drivers of CH1~CH3 if a
short-circuit condition continues for more than a certain period of time. The timer latch time is counted by the CH1 internal
switching pulse. The counting is started when a short-circuit condition begins, ant the drivers are turned off when 131,072
is reached.
Example) if RRT=120kΩ, then 131072×(1/1[MHz])=131.072ms
Detects abnormal heat generation of the IC, stops the switching operation of all Ch and prevents the IC from thermal
overload. The detecting temperature is 175℃(typ), and the hysteresis is 10℃(typ).
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Technical Note
2010.03 - Rev.A