rt9204 ETC-unknow, rt9204 Datasheet - Page 10

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

RT9204
Input / Output Capacitor
High frequency/long life decoupling capacitors should
be placed as close to the power pins of the load as
physically possible. Be careful not to add inductance
to the PCB trace, as it could eliminate the
performance from utilizing these low inductance
components. Consult with the manufacturer of the
load on specific decoupling requirements.
The output capacitors are necessary for filtering
output and stabilizing the close loop (see the PWM
loop stability). For powering advanced, high-speed
processors,
requirement of fast load transient, high frequency
capacitors
recommended.
Another concern is high ESR induced ripple may
trigger UV or OV protections.
Linear Regulator Driver
The linear regulator of RT9204 was designed to drive
bipolar NPN or MOSFET pass transistor. For
MOSFET pass transistor, normally DRV need to
provide minimum V
keep V
MOSFET operating at 5V power supply system, the
gate-drive will be limited at 5V. In this situation shown
in Fig. 5, low VT threshold MOSFET (VT = 1V) and
Vout2 setting below 2.5V were suggested. In V
= 12V operation condition as Fig. 6, VCC is regulated
as higher to 6V providing more gate-drive for pass
MOSFET transistor, V
www.richtek-ic.com.tw
10
VCC = 5V
OUT2
with
it
as setting voltage. When driving
VCC
BOOT
is
RT9204
low
DRV
OUT2
required
OUT2
FBL
Fig. 5
ESR/ESL
+VT+gate-drive voltage to
can be set as ≤ 3.3V.
R3
R4
to
R4 < 1K
V
meet
+
capacitors
OUT2
≤ 2.5V
with
BOOT
Preliminary
are
the
PWM Loop Stability
The RT9204 is a voltage mode buck controller
designed for 5V step-down applications. The gain of
error amplifier is fixed at 35dB for simplified design.
The output amplitude of ramp oscillator is 1.6V, the
loop gain and loop pole/zero are calculated as
follows:
The RT9204 Bode plot as shown Fig.7 is stable in
most of application conditions.
40
30
20
10
V
DC loop gain G
LC filter pole P
Error Amp pole P
ESR zero Z
BOOT
V
V
V
V
C
L=2 µ H
OUT
OUT
OUT
100
OUT
OUT
= 1.5V
= 2.5V
= 3.3V
= 12V
= 3.3V
= 1500 µ F(33m Ω )
6V
O
VCC
BOOT
=
RT9204
O
DRV
A
1
2
=
1k
= 35dB ×
A
P
× π × ESR × C
FBL
O
Loop Gain
2
= 300kHz
1
= 2.9kHz
Fig. 6
× π ×
Fig. 7
R3
R4
DS9204-00 February 2002
Z
O
1
10k
= 3.2kHz
5
6 .
LC
R4 < 1K
×
V
VOUT
+
OUT2
0
8 .
≤ 3.3V
100k
1M