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IR3080PBF Datasheet, PDF (28/41 Pages) International Rectifier – XPHASETM VRD10 CONTROL IC WITH VCCVID & OVERTEMP DETECT
◁
IR3080PbF
The power good delay time is
tVccPG
=
CSS / DEL
* (3.91−VO
ICHG
− 1.3)
=
0.1*10−6 * (3.91−1.33 −1.3)
70 *10−6
= 1.8ms
VDAC Slew Rate Programming Capacitor CVDAC and Resistor RVDAC
From Figure 15, the sink current of VDAC pin corresponding to 400kHz (ROSC=30.1kΩ) is 76uA. Calculate the
VDAC down-slope slew-rate programming capacitor from the required down-slope slew rate.
CVDAC
=
I SINK
SRDOWN
=
76 *10−6
2.5 *10−3 /10−6
= 30.4nF , Choose CVDAC=33nF
Calculate the programming resistor.
RVDAC
= 0.5 + 3.2 *10−15
CVDAC 2
= 0.5 +
3.2 *10−15
(33 *10−9 )2
= 3.5Ω
From Figure 15, the source current of VDAC pin is 110uA. The VDAC up-slope slew rate is
SRUP
=
I SOURCE
CVDAC
=
110 *10−6
33 *10−9
= 3.3mV / 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)] = 0.47*10−3 ∗[1+ 3850*10−6 ∗(100− 25)] = 0.61mΩ
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, the bias current of OCSET pin (IOCSET) is 41uA with
ROSC=30.1kΩ. 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
I LIMIT / n
∗
f SW
∗ 2)
=
(12 −1.33) ∗1.33 /(220 *10−9
135 / 6
∗12 ∗ 400 *103
∗ 2)
=
0.3
ROCSET
= [ ILIMIT
n
∗ RL _ MAX
∗ (1 + KP ) + VCS _ TOFST ] ∗ GCS _ MIN
/ IOCSET
= (135 ∗ 0.61*10 −3 ∗1.3 + 0.55 *10 −3 ) ∗ 30.2 /(41*10 −6 ) = 13.3kΩ
6
No Load Output Voltage Setting Resistor RFB and Adaptive Voltage Positioning Resistor RDRP
From Figure 14, the bias current of FB pin is 41uA with ROSC=30.1kΩ.
R FB
=
RL _ MAX
∗ VO _ NLOFST − VCS _ TOFST
I FB ∗ RL _ MAX
∗ n ∗ RO
=
0.61 *10 −3 ∗ 20 *10−3 − 0.55 *10−3 ∗ 6 ∗ 0.91 *10−3
41 *10 −6 ∗ 0.61 *10−3
= 365Ω
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