参数资料
型号: IR3081AMPBF
厂商: International Rectifier
文件页数: 27/39页
文件大小: 0K
描述: IC CTRLR XPHASE VR10.0 28MLPQ
标准包装: 100
系列: XPhase™
应用: 处理器
电流 - 电源: 11mA
电源电压: 9.5 V ~ 14 V
工作温度: 0°C ~ 100°C
安装类型: 表面贴装
封装/外壳: 28-MLPQ
供应商设备封装: 28-MLPQ(5x5)
包装: 剪切带 (CT)
IR3081A
VDAC Slew Rate Programming Capacitor C VDAC and Resistor R VDAC
From Figure 15, the sink current of VDAC pin corresponding to 400kHz (R OSC =30.1k ? ) is 76uA. Calculate the
VDAC down-slope slew-rate programming capacitor from the required down-slope slew rate.
C VDAC =
I SINK
SR DOWN
=
76 * 10 ? 6
2 . 5 * 10 ? 3 / 10 ? 6
= 30 . 4 nF , Choose C VDAC =33nF
Calculate the programming resistor.
R VDAC = 0 . 5 +
3 . 2 * 10 ? 15
C VDAC 2
= 0 . 5 +
3 . 2 * 10 ? 15
( 33 * 10 ? 9 ) 2
= 3 . 5 ?
From Figure 15, the source current of VDAC pin is 110uA. The VDAC up-slope slew rate is
SR UP =
I SOURCE
C VDAC
=
110 * 10 ? 6
33 * 10 ? 9
= 3 . 3 mV / uS
Over Current Setting Resistor R OCSET
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,
R L _ MAX = R L _ ROOM ? [ 1 + 3850 * 10 ? 6 ? ( T L _ MAX ? T ROOM )] = 0 . 47 * 10 ? 3 ? [ 1 + 3850 * 10 ? 6 ? ( 100 ? 25 )] = 0 . 61 m ?
The current sense amplifier gain is 34 at 25oC, and its gain at 101oC is calculated as,
G CS _ MIN = G CS _ ROOM ? [ 1 ? 1470 * 10 ? 6 ? ( T IC _ MAX ? T ROOM )] = 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 (I OCSET ) is 41uA with
R OSC =30.1k ? . 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 K P, the ratio of inductor peak current over average current in each phase,
K P =
( V I ? V O ) ? V O /( L ? V I ? f SW ? 2 )
I LIMIT / n
=
( 12 ? 1 . 33 ) ? 1 . 33 /( 220 * 10 ? 9 ? 12 ? 400 * 10 3 ? 2 )
135 / 6
= 0 . 3
R OCSET = [
I LIMIT
n
? R L _ MAX ? ( 1 + K P ) + V CS _ TOFST ] ? G CS _ MIN / I OCSET
= (
135
6
? 0 . 61 * 10 ? 3 ? 1 . 3 + 0 . 55 * 10 ? 3 ) ? 30 . 2 /( 41 * 10 ? 6 ) = 13 . 3 k ?
No Load Output Voltage Setting Resistor R FB and Adaptive Voltage Positioning Resistor R DRP
From Figure 14, the bias current of FB pin is 41uA with R OSC =30.1k ? .
R FB =
R L _ MAX ? V O _ NLOFST ? V CS _ TOFST ? n ? R O
I FB ? R L _ MAX
=
0 . 61 * 10 ? 3 ? 20 * 10 ? 3 ? 0 . 55 * 10 ? 3 ? 6 ? 0 . 91 * 10 ? 3
41 * 10 ? 6 ? 0 . 61 * 10 ? 3
= 365 ?
R DRP =
R FB ? R L _ MAX ? G CS _ MIN
n ? R O
=
365 ? 0 . 61 * 10 ? 3 ? 30 . 2
6 ? 0 . 91 * 10 ? 3
= 1 . 21 k ?
Page 27 of 39
1/31 /05
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