BD9775FV-E2 Rohm Semiconductor, BD9775FV-E2 Datasheet - Page 9

• Manufacturer Part Number: BD9775FV-E2
• Description: IC REG SW STEP DOWN HE 28-SSOP
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9775FV-E2

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Current - Output: 400mA
• Frequency - Switching: 100kHz
• Voltage - Input: 6 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Power - Output: 640mW
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: BD9775FV-E2TR

(4) Feedback resistor design
(6) Setting the soft start delay
(5) Setting switching frequency
Please refer to the following equation in determining the proper feedback resistance. The recommended setting is in a range
between 10kΩ and 330kΩ. Resistance less than 10kΩ risks decreased power efficiency, while setting the resistance value
higher than 330kΩ will result in an internal error amp input bias current of 0.2uA increasing the offset voltage.
The triangular wave switching frequency can be set by connecting a resistor to the RT 15(33) pin. The RT sets the frequency
by adjusting the charge/discharge current in relation to the internal capacitor. Refer to the figure below in determining proper
RT resistance, noting that the recommended resistance setting is between 50kΩ and 130kΩ. Settings outside this range
may render the switching function inoperable, and proper operation of the controller overall cannot be guaranteed when
unsupported resistance values are used.
The soft start function is necessary to prevent an inrush of coil current and output voltage overshoot at startup. The figure
below shows the relation between soft start delay time and capacitance, which can be calculated using equation (12) at right.
overshoots. Please use high accuracy components (such as X5R) when implementing sequential startups involving other
power sources. Be sure to test the actual devices and applications to be used, since the soft start time varies, depending on
input voltage, output voltage and capacitance, coils and other characteristics.
Recommended capacitance values are between 0.01uF and 0.1uF. Capacitance lower than 0.01uF may generate output
Fig-22 SS capacitance vs. delay time
550
500
450
400
350
300
250
0.01
Vo
0.1
R8
R9
10
1
0.001
50
SS CAPACITANCE[uF]
60
Fig-20
FB
0.01
Internal ref. 0.8V
70
Fig-21 RT vs. switching frequency
0.1
80
RT [ kΩ]
9/29
90
TSS =
Vo =
100
0.8V(typ.)×CSS
ISS(10μA Typ.)
R8 +R9
R9
110
× 0.8 [V] ・・・ （11）
[sec]・・・(12)
120
130