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| 型號： | S-8520C25MC-BRK-T2 |
| 英文描述： | Analog IC |
| 中文描述： | 模擬IC |
| 文件頁數(shù)： | 16/37頁 |
| 文件大?。?/td> | 599K |
| 代理商： | S-8520C25MC-BRK-T2 |
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PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
S-8520/8521 Series
Rev.7.2
Seiko Instruments Inc.
16
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 ))
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.
(Note: // denotes a combined resistance in parallel.)
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
) 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 1.5 V to 2.0 V
→
5.16 M
to 28.9 M
Output voltage 2.1 V to 2.5 V
→
4.44 M
to 27.0 M
Output voltage 2.6 V to 3.3 V
→
3.60 M
to 23.3 M
Output voltage 3.4 V to 4.9 V
→
2.44 M
to 19.5 M
Output voltage 5.0 V to 6.0V
→
2.45 M
to 15.6 M
When a value of R1+R2 given by the equation indicated below is taken in calculating the voltage value
of the output OUT, a median voltage deviation will be obtained for the output OUT.
R1 + R2 = 2 ÷ (1 ÷ maximum deviation in absolute value of internal resistances R1 and R2 in IC + 1 ÷
minimum deviation in absolute value of internal resistances R1 and R2 of IC)
Moreover, add a capacitor CC in parallel to the external resistance RA in order to avoid output
oscillations and other types of instability (See Figure 11).
Make sure that CC is larger than the value given by the following equation:
CC (F)
≥
1
÷
(2 x
π
x RA (
) x 7.5 kHz)
If a large CC-value is selected, a longer soft-start time than the one set up in the IC will be set.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| S-8520C25MC-BRKT2G | 功能描述:DC/DC 開關(guān)控制器 2.5V 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-8520C25MC-BVK-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 |
| S-8520C27MC-BRM-T2 | 功能描述:DC/DC 開關(guān)控制器 2.7V 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-8520C27MC-BRMT2G | 功能描述:DC/DC 開關(guān)控制器 2.7V 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-8520C27MC-BVM-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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