bd9575fv-e2 ROHM Co. Ltd., bd9575fv-e2 Datasheet - Page 13

• Manufacturer Part Number: bd9575fv-e2
• Description: Switching Regulators Ddr-sdram Cores
• Manufacturer: ROHM Co. Ltd.

© 2009 ROHM Co., Ltd. All rights reserved.
BD9575FV
www.rohm.com
6.Setting frequency
7. Setting standard voltage (REF)
R1
R2
V
Outside
voltage
OUT
VREG
3000
2500
2000
1500
1000
500
REF
V
1200
1000
800
600
400
200
0
OUT
REF
0
0
0
VIN=5V
50
50
12V
16V
19V
7V
Resistance [kΩ]
RFS [kΩ]
100
CONTROLLA
100
CONTROLLA
H
3
H
Calculated frequency
Reg
V
3
VIN=5V
IN
using TON above
Reg
REF=1.8V
150
V
150
TM
IN
12V
16V
19V
7V
TM
200
200
R
S
R
S
Q
13/20
Q
On Time (TON) at steady state is determined by
resistance value connected to FS pin as shown in the
figure. The frequency can be calculated with TON,
input voltage VIN, the reference voltage REF as
follows.
However, the actual frequency becomes lower than
the formula due to expanded TON time caused by the
rise/fall time of the MOSFET (This rise/fall time is
affected by the switching speed). TON is also
influenced by Dead Time under light load in
continuous mode. In this case the frequency
becomes lower than setting frequency.
The setting frequency noted above is under heavy
load (when the inductor current does not go back to
VIN through the body diodes of the external
MOSFET’s).
It is available to synchronize setting the reference
voltage (REF) with outside supply voltage [V] by using
outside power supply voltage.
It is available to set the reference voltage (REF) by the
resistance division value from VREG in case it is not
set REF from an external power supply.
REF=
F=
V
IN
R1+R2
×T
REF
R2
ON
×VREG [V]・・・(16)
・・・(15)
Technical Note
2009.04 - Rev.B