IR3086AMPBF 데이터 시트보기 (PDF) - International Rectifier
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IR3086AMPBF Datasheet PDF : 33 Pages
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IR3086APbF
CVDAC
=
I SINK
SRDOWN
=
170 *10−6
2.5 *10−3 /10−6
= 68nF
Calculate the programming resistor.
RVDAC
= 0.5 + 3.2 *10−15
CVDAC 2
=
0.5
+
3.2 *10−15
(68 *10−9 )2
= 1.2Ω
From Figure 15 of IR3081A Data Sheet, the source current of VDAC pin is 250uA. The VDAC up-slope slew rate is
SRUP
=
I SOURCE
CVDAC
=
250 *10−6
68*10 −9
= 3.7mV
/ uS
Over Current Setting Resistor ROCSET
The room temperature is 25ºC and the target PCB temperature is 100 ºC. The phase IC die temperature is about 1
ºC higher than that of phase IC, and the inductor temperature is close to PCB temperature.
Calculate Inductor DC resistance at 100 ºC,
RL _ MAX = RL _ ROOM ∗[1+ 3850*10−6 ∗ (TL _ MAX − TROOM)] = 0.5*10−3 ∗[1+ 3850*10−6 ∗ (100− 25)] = 0.64mΩ
The current sense amplifier gain is 34 at 25ºC, and its gain at 101ºC is calculated as,
GCS _ MIN = GCS _ ROOM ∗[1 −1470 *10 −6 ∗ (TIC _ MAX − TROOM )] = 34 ∗[1 −1470 *10 −6 ∗ (101 − 25)] = 30.2
Set the over current limit at 135A. From Figure 14 of IR3081A Data Sheet, the bias current of OCSET pin (IOCSET)
is 90uA with ROSC=13.3kΩ. The total current sense amplifier input offset voltage is 0.55mV, which includes the
offset created by the current sense amplifier input resistor mismatch.
Calculate constant KP, the ratio of inductor peak current over average current in each phase,
KP
=
(VI
− VO ) ∗VO /(L ∗VI
ILIMIT / n
∗
f SW
∗ 2)
=
(12 −1.28) ∗1.28 /(100 *10−9
135 / 6
∗12 ∗800 *103
∗ 2)
=
0.32
ROCSET
= [ RLIMIT
n
∗ RL _ MAX
∗ (1 + KP ) + VCS _ TOFST ] ∗ GCS _ MIN
/ IOCSET
= (135 ∗ 0.64 *10 −3 ∗1.32 + 0.55 *10 −3 ) * 30.2 /(90 *10 −6 ) = 6.34kΩ
6
No Load Output Voltage Setting Resistor RFB and Adaptive Voltage Positioning Resistor RDRP
From Figure 14 of IR3081A Data Sheet, the bias current of FB pin is 90uA with ROSC=13.3kΩ.
RFB
=
RL _ MAX
∗VO _ NLOFST − VCS _ TOFST
I FB ∗ RL _ MAX
∗ n ∗ RO
=
0.64 *10−3 ∗ 20 *10−3 − 0.55*10−3 ∗ 6 ∗ 0.91*10−3
90 *10−6 * 0.64 *10−3
= 162Ω
RDRP
=
RFB ∗ RL _ MAX ∗ GCS _ MIN
n ∗ RO
=
162
∗ 0.64 *10−3 *30.2
6 ∗ 0.91*10−3
= 576Ω
Body BrakingTM Related Resistors RBBFB and RBBDRP
N/A. The body braking during Dynamic VID is disabled.
Page 26 of 33
9/30/04
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