BD9778F-E2 Rohm Semiconductor, BD9778F-E2 Datasheet - Page 9

• 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

2. Selection of coil (L)
3. Selection of output capacitor (Co)
1. Setting or output voltage
Description of external components
If this coil is not set to the optimum value, normal (continuous)
oscillation may not be achieved. Furthermore, set the value of
the coil with an adequate margin so that the peak current passing
through the coil will not exceed the rated current of the coil.
Set the rating of the capacitor with an adequate margin to the
output voltage. Also, set the maximum allowable ripple current
with an adequate margin to ∆IL. Furthermore, the output rise
time should be shorter than the soft start time. Select the output
capacitor having a value smaller than that obtained by the
formula shown below.
I
If this capacitance is not optimum, faulty startup may result.
( 3.5m is soft start time(min.))
Vo = Output voltage, Vin (Max.) = Maximum input voltage
Io (Max.) = Maximum load current, f = Oscillation frequency
The value of the coil can be obtained by the formula shown
below:
The output capacitor can be determined according to the
output ripple voltage ∆Vo (p-p) required.
Obtain the required ESR value by the formula shown below
and then select the capacitance.
Output voltage can be obtained by the formula shown below.
Use the formula to select the R1 and R2.
Furthermore, set the R2 to 30 kΩ or less.
Select the current passing through the R1 and R2 to be small
enough for the output current.
L
imit:2A(BD9778F/HFP,BD9001F), 4A(BD9781HFP)
L=(V
∆I
f = Operating frequency
∆Io should typically be approximately 20 to 30% of Io.
V
C
∆IL=(V
∆Vpp=∆IL x ESR+(∆IL x Vo)/(2 x Co x f x V
O
O:
Max
=1 x (1+R1/R2)
Output ripple current
IN
=
-V
IN
3.5m x (I
O
-V
) x V
O
) x V
Design procedure
O
/ (V
O
Limit
/(L x f x V
Vo
V
IN
-Io(Max))
IN
x f x ∆I
C
R
IN
T
O
)
)
C
C
in
T
C
SS
V
RT
SS
IN
IN
)
GND
Fig.30
INV
SW
FB
9/16
When Vo = 5 V and R2 = 10 kΩ ,
When I
C
When V
L=(13.2-5) x 5/13.2 x 1/100k x 1/(2 x 0.3)
=51.8μH
V
∆IL=(13.2-5) x 5/(100 x 10
IN
Max
=13.2V, Vo=5V, L=100μH, f=100kHz
C
=3.5m x (2-1)/5
=700μ
5=1 x (1+R1/10kΩ)
0.31
C
Limit
IN
Di
: 2 A, Io (Max) = 1 A, and Vo = 5V,
= 13.2 V, Vo = 5 V, Io = 2 A, and f = 100 kHz,
47μ
R
L
C
C
+
O
Calculation example
V
-6
O
R1
R2
x 100 x 10
3
x 13.2)
C
∆IL=0.31A
Max=
R1=40kΩ
L=47
700μF
μ
H