參數(shù)資料
型號(hào)： RT8004
廠商： Richtek Technology Corporation
英文描述： 3A, 4MHz, Synchronous Step-Down Regulator
中文描述： 第3A，4MHz，同步降壓型穩(wěn)壓器
文件頁(yè)數(shù)： 11/16頁(yè)
文件大小： 257K
代理商： RT8004
RT8004
11
DS8004-03 September 2007
www.richtek.com
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation :
The resistive divider allows the V
FB
pin to sense a fraction
of the output voltage as shown in Figure 1.
This formula has a maximum at V
IN
= 2V
OUT
, where
IRMS = I
OUT
/2. This simple worst-case condition is
commonly used for design because even significant
deviations do not offer much relief. Note that ripple current
ratings from capacitor manufacturers are often based on
only 2000 hours of life which makes it advisable to further
derate the capacitor, or choose a capacitor rated at a higher
temperature than required. Several capacitors may also
be paralleled to meet size or height requirements in the
design.
The selection of C
OUT
is determined by the effective series
resistance (ESR) that is required to minimize voltage ripple
and load step transients, as well as the amount of bulk
capacitance that is necessary to ensure that the control
loop is stable. Loop stability can be checked by viewing
the load transient response as described in a later section.
The output ripple,
Δ
V
OUT
, is determined by :
The output ripple is highest at maximum input voltage
since
Δ
I
L
inc
reases with input voltage. Multiple capacitors
placed in parallel may be needed to meet the ESR and
RMS current handling requirements. Dry tantalum, special
polymer, aluminum electrolytic and ceramic capacitors are
all available in surface mount packages. Special polymer
capacitors offer very low ESR but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density but it is important to only
use types that have been surge tested for use in switching
power supplies. Aluminum electrolytic capacitors have
significantly higher ESR but can be used in cost-sensitive
applications provided that consideration is given to ripple
current ratings and long term reliability. Ceramic capacitors
have excellent low ESR characteristics but can have a
high voltage coefficient and audible piezoelectric effects.
The high Q of ceramic capacitors with trace inductance
can also lead to significant ringing.
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, V
IN
. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at V
IN
large enough to damage the
part.
Frequency Synchronization
The RT8004
’
s internal oscillator can be synchronized to
an external clock signal. During synchronization, the top
MOSFET turn-on is locked to the falling edge of the
external frequency source. The synchronization frequency
range is 300kHz to 4MHz. Synchronization only occurs if
the external frequency is greater than the frequency set
by the external resistor. Because slope compensation is
generated by the oscillator
’
s RC circuit, the external
frequency should be set 25% higher than the frequency
set by the external resistor to ensure that adequate slope
compensation is present.
Soft-Start
The EN/SS pin provides a means to shut down the RT8004
as well as a timer for soft-start. Pulling the EN/SS pin
below 0.5V places the RT8004 in a low quiescent current
shutdown state (IQ < 1
μ
A).
+
≤
OUT
L
OUT
8fC
1
ESR
Δ
I
Δ
V
)
R1
R2
0.8V(1
V
OUT
+
=
Figure 1. Setting the Output Voltage
RT8004
GND
VFB
R2
R1
V
OUT
相關(guān)PDF資料
PDF描述
RT8004PCP 3A, 4MHz, Synchronous Step-Down Regulator
RT8004PQV 3A, 4MHz, Synchronous Step-Down Regulator
RT8004PS 3A, 4MHz, Synchronous Step-Down Regulator
RT8004QCP 3A, 4MHz, Synchronous Step-Down Regulator
RT8004QQV 3A, 4MHz, Synchronous Step-Down Regulator
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
RT8004GCP 功能描述:IC REG BUCK SYNC ADJ 3A 16TSSOP RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:50 系列:- 類(lèi)型:升壓（升壓） 輸出類(lèi)型:可調(diào)式 輸出數(shù):1 輸出電壓:5 V ~ 25 V 輸入電壓:2.3 V ~ 5.5 V PWM 型:電流模式 頻率 - 開(kāi)關(guān):600kHz，1.2MHz 電流 - 輸出:1A 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 包裝:管件 供應(yīng)商設(shè)備封裝:8-MSOP
RT8004GQV 功能描述:IC REG BUCK SYNC ADJ 3A 16VQFN RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開(kāi)關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:50 系列:- 類(lèi)型:升壓（升壓） 輸出類(lèi)型:可調(diào)式 輸出數(shù):1 輸出電壓:5 V ~ 25 V 輸入電壓:2.3 V ~ 5.5 V PWM 型:電流模式 頻率 - 開(kāi)關(guān):600kHz，1.2MHz 電流 - 輸出:1A 同步整流器:無(wú) 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 包裝:管件 供應(yīng)商設(shè)備封裝:8-MSOP
RT8004PCP 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:3A, 4MHz, Synchronous Step-Down Regulator
RT8004PQV 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:3A, 4MHz, Synchronous Step-Down Regulator
RT8004PS 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:3A, 4MHz, Synchronous Step-Down Regulator
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