BD9778F-E2 Rohm Semiconductor, BD9778F-E2 Datasheet - Page 7

• Manufacturer Part Number: BD9778F-E2
• Description: IC REG SW 2A P-CH MOSF STDN SOP8
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9778F-E2

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1 ~ 35 V
• Current - Output: 2A
• Frequency - Switching: 50kHz ~ 500kHz
• Voltage - Input: 7 ~ 35 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOP
• Power - Output: 690mW
• No. Of Outputs: 1
• Output Voltage: 35V
• Output Current: 2A
• Voltage Regulator Case Style: SOP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC (18-Jun-2010)
• Base Number: 9778
• Input Voltage: 35 V
• Switching Frequency: 102 KHz
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: BD9778F-E2TR

SOFT START
OSC(Oscillator)
TSD(Thermal Shut Down)
CURRENT LIMIT
ON/OFF(BD9778F/HFP,BD9781HFP)
PWM COMPARATOR
ERROR AMP
The ERROR AMP block is an error amplifier used to input the reference voltage (1 V typ.) and the INV pin voltage. The output
FB pin controls the switching duty and output voltage Vo. These INV and FB pins are externally mounted to facilitate phase
compensation. Inserting a capacitor and resistor between these pins enables adjustment of phase margin. (Refer to
recommended examples on page 11.)
The SOFT START block provides a function to prevent the overshoot of the output voltage Vo through gradually increasing
the normal rotation input of the error amplifier when power supply turns ON to gradually increase the switching Duty. The soft
start time is set to 5 msec (Typ.).
Setting the EN pin to 0.8 V or less makes it possible to shut down the circuit. Standby current is set to 0 μA (Typ.).
Furthermore, on the BD9781HFP, applying a pulse having a frequency higher than set oscillation frequency to the EN/SYNC
pin allows for external synchronization (up to +50% of the set frequency).
The PWM COMPARATOR block is a comparator to make comparison between the FB pin and internal triangular wave and
output a switching pulse.
The switching pulse duty varies with the FB value and can be set in the range of 0 to 100%.
The OSC block is a circuit to generate a triangular wave that is to be input in the PWM comparator. Connecting a resistor to
the RT pin enables setting of oscillation frequency.
In order to prevent thermal destruction/thermal runaway of this IC, the TSD block will turn OFF the output when the chip
temperature reaches approximately 150˚C or more. When the chip temperature falls to a specified level, the output will be
reset. However, since the TSD is designed to protect the IC, the chip junction temperature should be provided with the thermal
shutdown detection temperature of less than approximately 150˚C.
While the output POWER P-ch MOS FET is ON, if the voltage between drain and source (ON resistance ¥ load current)
exceeds the reference voltage internally set with the IC, this block will turn OFF the output to latch. The overcurrent protection
detection values have been set as shown below:
Furthermore, since this overcurrent protection is an automatically reset, after the output is turned OFF and latched, the latch will
be reset with the RESET signal output by each oscillation frequency.
However, this protection circuit is only effective in preventing destruction from sudden accident. It does not support for the
continuous operation of the protection circuit (e.g. if a load, which significantly exceeds the output current capacitance, is
normally connected). Furthermore, since the overcurrent protection detection value has negative temperature characteristics,
consider thermal design.
Description of operations
BD9781HFP . . . 8A(Typ.)
BD9001F,BD9778F/HFP . . . 4A(Typ.)
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