전자부품 데이터시트 검색엔진 |
|
TC573002 데이터시트(PDF) 4 Page - Microchip Technology |
|
TC573002 데이터시트(HTML) 4 Page - Microchip Technology |
4 / 16 page TC57 DS21437B-page 4 © 2002 Microchip Technology Inc. 3.0 DETAILED DESCRIPTION The TC57 series of precision low dropout regulator controllers use an external PNP transistor to accommodate a wide range of output currents. A series resistor (RB) limits the maximum base current drawn from the PNP transistor. Limiting the base drive both determines the regulator’s output current capability, as well as limits ground current when the device is operated in dropout. The PNP transistor’s VCE(SAT) is the only factor limiting dropout voltage. FIGURE 3-1: TEST CIRCUIT 3.1 Transistor Selection The PNP pass transistor must have satisfactory power dissipation, current gain, and collector current specifi- cations to suit the application at hand. The maximum output current the circuit can deliver is influenced by hFE. The highest guaranteed output current is given by: EQUATION 3-1: The transistor’s actual power dissipation (PD) is equal to the maximum load current times the maximum input/ output voltage differential, or: EQUATION 3-2: The ideal transistor has a minimum hFE of 100, and a VCE(SAT) of less than 0.6V at full output current. For example, the Zetex FZT749 has an hFE of 170 at a collector current of 1A, and a guaranteed VCE(SAT) of 0.3V at a base current of 100mA. It is packaged in a SOT-223 and is recommended for use with the TC57. Other transistors are also suitable, depending on the required input and output voltages and output current (Table 3-1). 3.2 Base-Current Limiting Resistor Base current limiting resistor RB canbeestimated using: EQUATION 3-3: Where: hFE is the current gain of the pass transistor VIN Is the input voltage (in volts) VBE is the base-emitter voltage at the desired output current (in volts) IOUT is the output current (in Amps) For example, assume a desired continuous output current of 1.0A, an input voltage of 5V, and an FZT749 pass transistor. The FZT749 has a typical hFE of 170, and a VBE of 0.8V; both specified at a collector current of 1.0A. Substituting these values into the equation above results in an RB value of 704Ω (closest standard value = 680 Ω). 3.3 Pull-Up Resistor and Output Capacitor A pull-up resistor (RBE, installed between the base and emitter of the pass transistor) facilitates rapid turn-off of the pass transistor in the event of a sudden decrease in load (Figure 3-2). Recommended values for this resistor are between 20K Ω and 47KΩ. A Tantalum output capacitor of at least 10 µFmust beusedto guarantee stability. Higher values decrease output noise and eliminate power-on overshoot, but extend power-up times. Table 3-1 lists several capacitor choices. FIGURE 3-2: 3.3V, 1A REGULATOR USING 5V SUPPLY INPUT TC573002ECT VOUT GND SHDN VIN EXT CIN 10µF (Tantalum) FZT749 Q1 RB 680 Ω CL 10 µF (Tantalum) RL VIN RBE 33K 1 2 ON OFF 3 4 5 VOUT ILOAD(MAX) =25mA x hFE(MIN) PD ≈ ILOAD(MAX) x(VIN(MAX) –VOUT(MIN)) hFE (VIN –VBE) IOUT RB = TC57 VOUT SHDN VIN EXT CIN 10µF (Tantalum) FZT749 Q1 RB 680 Ω COUT 10 µF (Tantalum) VIN = 5V RBE 33K Ω 1 2 ON OFF 3 4 5 VOUT = 3.3V GND |
유사한 부품 번호 - TC573002 |
|
유사한 설명 - TC573002 |
|
|
링크 URL |
개인정보취급방침 |
ALLDATASHEET.CO.KR |
ALLDATASHEET 가 귀하에 도움이 되셨나요? [ DONATE ] |
Alldatasheet는? | 광고문의 | 운영자에게 연락하기 | 개인정보취급방침 | 링크교환 | 제조사별 검색 All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |