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參數(shù)資料
| 型號： | RT9203 |
| 英文描述： | Step-down DC/DC Converter |
| 中文描述： | 降壓直流/直流轉(zhuǎn)換器 |
| 文件頁數(shù)： | 13/16頁 |
| 文件大小： | 315K |
| 代理商： | RT9203 |
Preliminary
RT9203/A
DS9203/A-04 May 2003
www.richtek.com
13
Reference Voltage
Because RT9203/A uses a low 35dB gain error
amplifier, as shown in Fig.10. The voltage regulation is
dependent on V
IN
and V
OUT
settings. The FB reference
voltage of 0.8V were trimmed at V
IN
= 5V and V
OUT
=
2.5V. In a fixed V
IN
= 5V application, the FB reference
voltage vs. V
OUT
voltage can be calculated as Fig.11.
Fig. 10
Fig. 11
Feedback Divider
The reference of RT9203/A is 0.8V. The output voltage
can be set using a resistor-divider as shown in Fig.12.
Put the R1 and R2 as close as possible to FB pin. R2
value should be less than 1 k
to avoid noise coupling
issue. The C1 capacitor is a speed-up capacitor for
reducing output ripple to meet with the requirement of
fast transient load. Typically a 1nF ~ 0.1
μ
F is enough
for C1.
Fig. 12
PWM Layout Considerations
MOSFETs switch very fast in efficiency. The speed
with which the current transitions from one device to
another
causes
voltage
interconnecting impedances and parasitic circuit
elements. The voltage spikes can degrade efficiency
and radiate noise, that results in over-voltage stress
on devices. Careful the layout for component
placement and printed circuit design can minimize the
voltage spikes induced in the converter. Consider, as
an example, the turn-off transition of the upper
MOSFET prior to turn-off, the upper MOSFET was
carrying the full load current. During turn-off, current
stops flowing in the upper MOSFET and is picked up
by the lower MOSFET or Schottky diode. Any
inductance in the switched current path generates a
large voltage spike during the switching interval. Care
with component selections, layout of the critical
components, and use shorter and wider PCB traces
that help in minimizing the magnitude of voltage
spikes.
spikes
across
the
There are two sets of critical components in a DC-DC
converter using the RT9203/A. The switching power
components are most critical because they switch
large amounts of energy, and as such, they tend to
generate equally large amounts of noise. The critical
small signal components are those connected to
sensitive nodes or those supplying critical bypass
current.
The power components and the PWM controller
should be placed firstly. Place the input capacitors,
especially the high-frequency ceramic decoupling
capacitors, close to the power switches. Place the
+
_
+
_
EA
+
PWM
_
REP
0.8V
I3
56K
I2
1K
FB
RAMP
1.75V
VOUT = VFB
×
(1+
2
1
R
R
)
F
Duty
(%)
VIN = 5V
80
70
60
20
30
40
50
0.82
0.78
0.80
0.81
0.79
10
90
V
FB
= 0.8
100
50
Duty
×
6.25mV
VIN
C
OUT
+
V
OUT
RT9203/A
FB
L
R1
<
1K
C1
R2
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| RT9203AGS | 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:Dual Regulators - Synchronous Buck PWM DC-DC and Linear Controller |
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| RT9203GS | 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:Dual Regulators - Synchronous Buck PWM DC-DC and Linear Controller |
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| RT9204 | 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:Dual Regulators - Standard Buck PWM DC-DC and Linear Controller |
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