參數(shù)資料
型號: S-817B30AMC-CWT-T2
廠商: Seiko Instruments Inc.
英文描述: SUPER-SMALL PACKAGE CMOS VOLTAGE REGULATOR
中文描述: 超小型封裝CMOS電壓穩(wěn)壓器
文件頁數(shù): 9/28頁
文件大?。?/td> 412K
代理商: S-817B30AMC-CWT-T2
Rev.2.3
S-817 Series
ULTRA COMPACT CMOS VOLTAGE REGULATOR
Seiko Instruments Inc.
9
Operation
1. Basic Operation
Figure 9 shows the block diagram of the S-817
series.
The error amplifier compares a reference voltage
V
ref
with a part of the output voltage divided by the
feedback resistors Rs and Rf, and supplies the gate
voltage to the output transistor, necessary to ensure
certain output voltage independent from change of
input voltage and temperature.
2. Output Transistor
The S-817 series uses a Pch MOS transistor as the output transistor.
The voltage at VOUT must not exceed VIN+0.3V. When the VOUT voltage becomes higher than that of VIN,
reverse current flows and may break the regulator since a parasitic diode between VOUT and VIN exists
inevitably.
3. Short Circuit Protection
The S-817A series incorporates a short circuit protection to protect the output transistor against short circuit
between VOUT pin and VSS pin. Installation of the short-circuit protection which protects the output transistor
against short-circuit between VOUT and VSS can be selected in the S-812C series. The short-circuit
protection controls output current as shown in the typical characteristics, (1) OUTPUT VOLTAGE versus
OUTPUT CURRENT, and suppresses output current at about 40 mA even if VOUT and VSS pins are short-
circuited.
The short-circuit protection can not at the same time be a thermal protection. Attention should be paid to the
Input voltage and the load current under the actual condition so as not to exceed the power dissipation of the
package including the case for short-circuit.
When the output current is large and the difference between input and output voltage is large even if not
shorted, the short-circuit protection may work and the output current is suppressed to the specified value.
Products without short-circuit protection can provide comparatively large current by removing a short-circuit
protection.
For details, refer to (3) MAXIMUM OUTPUT CURRENT versus INPUT VOLTAGE curve.
The S-817B series can provide comparatively large current by removing a short circuit protection.
Selection of Output Capacitor (CL)
To stabilize operation against variation in output load, a capacitor (CL) must be mounted between VOUT and
VSS in the S-817 series because the phase is compensated with the help of the internal phase compensation
circuit and the ESR of the output capacitor.
When selecting a ceramic or an OS capacitor, capacitance should be 0.1
μ
F or more, and
when selecting a tantalum or an aluminum electrolytic capacitor, capacitance should be 0.1
μ
F or more and
ESR 30
or less.
When an aluminum electrolytic capacitor is used attention should be especially paid to since the ESR of the
aluminum electrolytic capacitor increases at low temperature and possibility of oscillation becomes large.
Sufficient evaluation including temperature characteristics is indispensable.
Overshoot and undershoot characteristics differ depending upon the type of the output capacitor.
Refer to CL dependencies in “TRANSIENT RESPONSE CHARACTERISTICS”.
Reference
voltage
circuit
VOUT
*1
*1 Parasitic diode
VSS
VIN
Rs
Rf
Error amplifier
Current
source
Vref
Figure 9 Block Diagram
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