BD95500MUV Datasheet, PDF (13/21 Pages) Rohm – Switching Regulator with MOSFET for DDR-SDRAM Cores

BD95500MUV
Technical Note
4. Setting Detection Resistance
VIN
HG
SW
L
R
IL
LG
PGND
Is+
Is-
Current limit
VOUT
Co
The over current protection function detects the output ripple current peak
value. This parameter (setting value) is determined as in formula (10)
below.
ILMIT= ^VILIM×0.1 [A]・・・(10)
R
(VILIM: ILIM voltage, R: Detection resistance)
VIN
HG
SW
IL
L RL
LG
PGND
r
C
Is+
Is-
Current limit
VOUT
Co
When the over current protection is detected by DCR of coil L, this
parameter (setting value) is determined as in formula (11) below.
ILMIT=VILIM×0.1×
r×C
L
[A]・・・(11)
L
(RL= _r×C )
(VILIM:ILIM voltage, RL: the DCR value of coil)
IL
ILIMIT
detect point
0
t
As soon as the voltage drop between Is+ and Is- generated by the inductor
current becomes specific threshold, the gate voltage of the high side
MOSFET becomes low.
Since the peak voltage of the inductor ripple current is detected, this
operation can sense high current ripple operation caused by inductance
saturated rated current and lead to high reliable systems.
VIN
HG
SW
L
R
LG
PGND
IL
R1 R1
Is+
Is-
VOUT ^{Current limit}
R2 R2
VOUT
When the output voltage is 2.7V or more, use the resistance for setting
output voltage like left figure, for Is+ and Is-.
According to the setting value above, ILIMIT setting current is in proportion
to the divided ratio.
Co
ILMIT=
R1+R2
R1
×
VLIMIT×0.1
R
[A]・・・(12)
(VILIM: ILIM voltage R: Detection resistance)
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13/20
2010.05 - Rev.C