參數(shù)資料
型號: UCC284SDR-5EP
廠商: TEXAS INSTRUMENTS INC
元件分類: 固定負電壓單路輸出LDO穩(wěn)壓器
英文描述: 5 V FIXED NEGATIVE LDO REGULATOR, 0.55 V DROPOUT, PDSO8
封裝: GREEN, PLASTIC, MS-012AA, SOIC-8
文件頁數(shù): 5/21頁
文件大?。?/td> 506K
代理商: UCC284SDR-5EP
VIN TO VOUT DELAY TIME
DURING POWER-UP WITH CT = 0.22
F
VIN to VOUT Delay
5
4
1
3
2
R1
R2
VOUT
VOUTS
GND
6
7
VIN
CIN
VIN
8
CT
SD/CT
COUT
VOUT
+
(+)
C1
UCC384ADJ
R3
C2
2N7000
QUICK START CURRENT
R4
0.22
F
0.1
F
18 k
12 k
1
F
4.7
F
Q1
()
www.ti.com ....................................................................................................................................... SLVS862A – NOVEMBER 2008 – REVISED NOVEMBER 2008
Figure 9.
During power-up there is a delay between VIN and VOUT. The majority of this delay time is due to the charging
time of the CT capacitor. When VIN moves more negative than the UVLO of the device with respect to GND, the
CT capacitor begins to charge. A 17-
A current sink is used only during power up to charge the CT capacitor.
When the voltage on the SD/CT pin reaches approximately –1.6 V with respect to GND, the output turns on and
regulates. The larger the value of the CT capacitor, the greater the delay time between VIN and VOUT. Figure 9
shows the VIN to VOUT start-up delay, approximately 16 ms for a circuit with CT = 0.22
F.
Shorter delay times can be achieved with a smaller CT capacitor. The problem with a smaller CT capacitor is that
with a very large load, the circuit may stay in overcurrent mode and never turn on. A circuit with a large
capacitive load needs a large CT capacitor to operate properly.
One way to shorten the delay from VIN to VOUT during powerup is with the use of the quick start-up circuit
shown in Figure 10.
Figure 10. Quick Start-Up Circuit
Copyright 2008, Texas Instruments Incorporated
13
Product Folder Link(s): UCC284-EP
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