rt9204 ETC-unknow, rt9204 Datasheet - Page 11

• Manufacturer Part Number: rt9204
• Description: Dual Regulator - Standard Buck Pwm Dc-dc And Linear Power Controller
• Manufacturer: ETC-unknow

Reference Voltage
Because RT9204 use a low 35dB gain error amplifier,
shown in Fig. 8. The voltage regulation is dependent
on V
0.8V were trimmed at V
condition. In a fixed V
reference voltage vs. V
as Fig. 9.
Feedback Divider
The reference of RT9204 is 0.8V. Both the PWm and
LDO output voltages can be set using a resistor
based divider as shown in Fig.9. Put the R1&R2 and
R3&R4 as close as possible to FB pin and R2&R4
should be less than 1 kΩ to avoid noise coupling. The
C1 capacitor is a speed-up capacitor for reducing
output ripple to meet with the requirement of fast
transient load. Typically a 1nF ~ 0.1µF is enough for
C1.
DS9204-00 February 2002
0.82
0.81
0.8
0.79
0.88
IN
0.5
FB
& V
_
OUT
1
setting. The FB reference voltage of
1.5
1K
REP
0.8V
I2
2
OUT
Fig. 8
Fig. 9
IN
V
= 5V application, the FB
1.75V
OUT
IN
_
voltage can be calculated
2.5
EA
56K
= 5V & V
I3
(V)
RAMP
3
3.5
_
PWM
OUT
VIN = 5V
4
= 2.5V
4.5
Preliminary
V
V
OUT
OUT
PWM Layout Considerations
MOSFETs switch very fast and efficiently. The speed
with which the current transitions from one device to
another
interconnecting impedances and parasitic circuit
elements. The voltage spikes can degrade efficiency
and radiate noise, that results in ocer-voltage stress
on devices. Careful component placement layout 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 low side
MOSFET or Schottky diode. Any inductance in the
switched current path generates a large voltage spike
during the switching interval. Careful component
selections, layout of the critical components, and use
shorter and wider PCB traces help in minimizing the
magnitude of voltage spikes.
There are two sets of critical components in a DC-DC
converter using the RT9204. 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.
1
2
=
=
0
0
8 .
8 .
V
V
L
VIN
×
×
causes
1 (
1 (
+
+
R
R
R
R
+
2
1
3
4
C
)
)
OUT
voltage
R1
R2
R2 < 1K
Fig. 10
V
OUT1
C1
spikes
FB
RT9204
www.richtek-ic.com.tw
FBL
DRV
RT9204
across
R3
R4
R4 < 1K
+
the
11
V
OUT2