BD9778F-E2 Rohm Semiconductor, BD9778F-E2 Datasheet - Page 11

• 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

1.
※ As shown above, design the GND pattern as large area as possible
※ Gray zones indicate GND.
within inner layer.
Phase compensation setting procedure
The following section describes the stability conditions of the negative feedback system.
Since the DC/DC converter application is sampled according to the switching frequency, GBW (frequency at 0-dB gain)
of the overall system should be set to 1/10 or less of the switching frequency. The following section summarizes the targeted
characteristics of this application.
・ At a 1 (0-dB) gain, the phase delay is 150˚ or less (i.e., the phase margin is 30˚ or more).
・ The GBW for this occasion is 1/10 or less of the switching frequency.
Responsiveness is determined with restrictions on the GBW. To improve responsiveness, higher switching frequency
should be provided.
Replace a secondary phase delay (-180˚) with a secondary phase lead by inserting two phase leads, to ensure the stability
through the phase compensation. Furthermore, the GBW (i.e., frequency at 0-dB gain) is determined according to phase
compensation capacitance provided for the error amplifier. Consequently, in order to reduce the GBW,
increase the capacitance value.
Application stability conditions
※Oscillation frequency s graph value is Typical value,
Fig.32 BD9001F reference layout pattern
oscillation frequency is necessary to consider
Fig.34 R
(1) Typical integrator (Low pass filter)
Since the error amplifier is provided with (1) or (2) phase compensation, the low pass filter is applied. In the case of
the DC/DC converter application, the R becomes a parallel resistance of the feedback resistance.
OSCILATING FREQUENCY SETTING RESISTANCE : R
Co
500
450
400
350
300
250
200
150
100
50
T
0
vs f
Feedback
L
100
OSC
200
Cx2
C3
R2
(BD9781HFP/BD9778F/HFP)
300
Di
R1
R
400
500
600
-
A
700
C
C
±
20% as dispersion.
800
T
[kΩ]
FB
11/16
Fig.33 BD9781HFP reference layout pattern
(2) Open loop characteristics of integrator
Phase
Gain
[dB]
[˚]
OSCILATING FREQUENCY SETTING RESISTANCE : RT [kΩ]
-180
0
-90
A
0
C
300
250
200
150
100
50
Di
Fig.35 R
Point (a) fa =
Point (b) fa = GBW =
50
100
L
200
(a)
T
300
R
C
Co
vs f
T
T
-90˚
400
Cx1
OSC
2 RCA
-20dB/decade
500
1
Phase
margin
(BD9001F)
600
[Hz]
2 RC
700
1
GBW(b)
800
[Hz]
-180˚
f
f