BD9001F Просмотр технического описания (PDF) - ROHM Semiconductor

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BD9001F

Flexible Step-down Switching Regulators with Built-in Power MOSFET

ROHM Semiconductor 

BD9778F, BD9778HFP, BD9001F, BD9781HFP

Technical Note

<Reference> Measurement of open loop of DC/DC converter

To measure the open loop of DC/DC converter, use the gain phase analyzer or FRA to measure the frequency

characteristics.

DC/DC converter

controller

VO

+

Vm

~

RL

<Procedure>

1. Check to ensure output causes no oscillation at the maximum

load in closed loop.

2. Isolate (1) and (2) and insert Vm (with amplitude of

approximately 100 mVpp).

3. Measure (probe) the oscillation of (1) to that of (2).

Load

0

Output voltage

Maximum load

Inadequate phase margin

Adequate phase margin

Furthermore, the phase margin can also be measured with the

load responsiveness.

Measure variations in the output voltage when instantaneously

changing the load from no load to the maximum load.

Even though ringing phenomenon is caused, due to low phase margin,

no ringing takes place. Phase margin is provided. However,

t no specific phase margin can be probed.

Heat loss

ºC

ºC

The heat loss W of the IC can be obtained by the formula shown below:

W=Ron X Io2 X

Vo

VIN

+ VIN X ICC + Tr X VIN X Io X f

Ron: ON resistance of IC (refer to pages 4 and 5.) Io: Load current Vo: Output voltage

VIN: Input voltage Icc: Circuit current (Refer to pages 2 and 3)

Tr: Switching rise/fall time (Approximately 40 nsec)

f : Oscillation frequency

Tr

VIN

SW

waveform

GND

1

2

T=

1

f

1 Ron X Io2

2

2

X

1

2

X Tr

X

1

T

X VIN X Io

=Tr X VIN X Io X f

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13/16

2010.02 - Rev. B

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