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參數(shù)資料
| 型號(hào)： | S-8520 |
| 廠商： | Seiko Instruments Inc. |
| 英文描述： | PWM Control Step-Down Switching Regulator-Controller(PWM 控制，步降開關(guān)穩(wěn)壓器-控制器) |
| 中文描述： | PWM控制降壓型開關(guān)穩(wěn)壓控制器（脈寬調(diào)制控制，步降開關(guān)穩(wěn)壓器-控制器） |
| 文件頁數(shù)： | 14/30頁 |
| 文件大?。?/td> | 650K |
| 代理商： | S-8520 |
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PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
Rev.6.1
S-8520/8521 Series
Seiko Instruments Inc.
13
n
Application Circuits:
1. External adjustment of output voltage
The S-8520/21 Series allows you to adjust the output voltage or to set the output voltage to a value over the preset output voltage
range (6V) of the products of this series, when external resistances RA, RB, and capacitor CC are added, as illustrated in Figure 11.
Moreover, a temperature gradient can be obtained by inserting a thermistor or other element in series with RA and RB.
S-8520/21Series
ON/OFF
CC
RA
RB
V
OUT
V
SS
-
+
V
IN
OUT
EXT
-
+
+
-
R2
R1
PWM or
PWM/PFM-
Switched Control
Circuit
Oscillation
Circuit
Reference Voltage
Source with Soft-Start
Figure 11
The S-8520 and 21 Series have an internal impedance of R1 and R2 between the V
OUT
and the V
SS
terminal, as shown in Figure 11.
Therefore, the output voltage (OUT) is determined by the output voltage value VOUT of the S-8520/21 Series, and the ratio of the
parallel resistance value of external resistance RB and internal resistances R1 + R2 of the IC, to external resistance RA. The output
voltage is expressed by the following equation:
OUT = VOUT + VOUT
′
RA
( RB // ( R1 + R2 ))
(Note: // denotes a combined resistance in parallel.)
The voltage accuracy of the output OUT set by resistances RA and RB is not only affected by the IC's output voltage accuracy
(VOUT ±2.4%), but also by the absolute precision of external resistances RA and RB in use and the absolute value deviations of
internal resistances R1 and R2 in the IC.
Let us designate the maximum deviations of the absolute value of external resistances RA and RB by Ramax and Rbmax,
respectively, the minimum deviations by Ramin and Rbmin, respectively, and the maximum and minimum deviations of the
absolute value of internal resistances R1 and R2 in the IC by (R1+R2)max and (R1+R2)min, respectively. Then, the minimum
deviation value OUTmin and the maximum deviation value OUTmax of the output voltage OUT are expressed by the following
equations:
OUTmin = VOUT
′
0.976 + VOUT
′
0.976
′
Ramin
( Rbmax // ( R1 + R2 )max )
OUTmax = VOUT
′
1.024 + VOUT
′
1.024
′
Ramax
( Rbmin // ( R1 + R2 )min )
The voltage accuracy of the output OUT cannot be made higher than the output voltage accuracy (VOUT ± 2.4%) of the IC itself,
without adjusting the external resistances RA and RB involved. The closer the voltage value of the output OUT and the output
voltage value (VOUT) of the IC are brought to one other, the more the output voltage remains immune to deviations in the absolute
accuracy of externally connected resistances RA and RB and the absolute value of internal resistances R1 and R2 in the IC.
In particular, to suppress the influence of deviations in internal resistances R1 and R2 in the IC, a major contributor to deviations in
the output OUT, the external resistances RA and RB must be limited to a much smaller value than that of internal resistances R1
and R2 in the IC.
On the other hand, a reactive current flows through external resistances RA and RB. This reactive current must be reduced to a
negligible value with respect to the load current in the actual use of the IC so that the efficiency characteristics will not be degraded.
This requires that the value of external resistance RA and RB be made sufficiently large.
However, too large a value (more than 1M
W
) for the external resistances RA and RB would make the IC vulnerable to external noise.
Check the influence of this value on actual equipment.
There is a tradeoff between the voltage accuracy of the output OUT and the reactive current. This should be taken into
consideration based on the requirements of the intended application.
Deviations in the absolute value of internal resistances R1 and R2 in the IC vary with the output voltage of the S-8520/21 Series,
and are broadly classified as follows:
Output voltage 1.5V to 2.0V
5.16M
W
to 28.9M
W
Output voltage 2.1V to 2.5V
4.44M
W
to 27.0M
W
Output voltage 2.6V to 3.3V
3.60M
W
to 23.3M
W
Output voltage 3.4V to 4.9V
2.44M
W
to 19.5M
W
Output voltage 5.0V to 6.0V
2.45M
W
to 15.6M
W
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| S-8520A20MC-AVFT2G | 功能描述:DC/DC 開關(guān)控制器 Step Down SWR PWM 180kHz 60uA Iq RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520A21MC-AVG-T2 | 功能描述:DC/DC 開關(guān)控制器 2.1V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520A21MC-AVGT2G | 功能描述:DC/DC 開關(guān)控制器 2.1V Step-Down PWM RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| S-8520A25MC-ARK-T2 | 制造商:SII 制造商全稱:Seiko Instruments Inc 功能描述:PWM CONTROL & PWM/PFM CONTROL STEP-DOWN SWITCHING REGULATOR-CONTROLLERS |
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