Preliminary
RT9204
Dual Regulator - Standard Buck PWM DC-DC and Linear
Power Controller
General Description
The RT9204 is a dual power controllers designed for
high performance graphics cards and computer
applications. The IC integrates a standard buck
controller, a linear regulator driver and protection
functions into a small 8-pin package.
The RT9204 uses a internal compensated voltage
mode PWM control for simple application design. An
internal 0.8V reference allows the output voltage to
be precisely regulated to low voltage requirement. A
fixed 600kHz oscillator reduce the component size for
saving board area.
The RT9204 protects the converter and regulator by
monitoring the output under voltage.
Applications
Motherboard Power Regulation for Computers
z
Subsystems Power Supplies
z
Cable Modems, Set Top Box, and DSL Modems
z
DSP and Core Communications processor
z
Supplies
Memory Power Supplies
z
Personal Computer Peripherals
z
Industrial Power Supplies
z
5V-Input DC-DC Regulators
z
Low Voltage Distributed Power Supplies
z
Features
z
Operate from 5V
z
0.8V Internal Reference
z
Voltage Mode PWM Control
z
Fast Transient Response
z
Fixed 600kHz Oscillator Frequency
z
Full 0~100% Duty Cycle
z
Internal Soft Start
z
Internal PWM Loop Compensation
Pin Configurations
Part Number Pin Configurations
GND
VCC
DRV
FBL
TOP VIEW
1
2
3
4
RT9204CS
(Plastic SOP-8)
Ordering Information
RT9204
Package type
S : SOP-8
Operating temperature range
C : Commercial standard
8
7
6
5
UGATE
BOO T
SD
FB
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1
RT9204
Typical Application Circuit
Preliminary
V
V
OU T2
1. 6V
220µF
AU X
3. 3V
C6
Q1
2D1802
+
R4
100
R5
100
R1
10
C5
1µF
1
GND
2
VCC
3
DRV
4
FBL
UGATE
RT9204
BOOT
SD
FB
R2
120
8
7
V
OU T1
2. 5V
6
5
R3
250
C7
10nF
Fig.1 RT9204 powered from 5V only
C3
0. 1µF
+
L1
5µH
C4
1000µF
MU
D1
C2
1µF
5V
+
C1
470µF
V
OU T2
1. 6V
220µF
V
3. 3V
AU X
C6
R1
10
C5
1µF
1
GND
2
VCC
Q1
R4
100
+
R5
100
3
4
C7
1µF
DRV
FBL
UGATE
RT9204
BOOT
SD
FB
R2
120
8
7
V
OU T1
2. 5V
6
5
R3
250
C3
10nF
5µH
+
C4
1000µF
L1
12V
MU
D1
C2
1µF
5V
+
C1
470µF
Fig.2 RT9204 powered from 12V
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2
C
VCC
1µF
GND
VCC
Layout Notes
1. Put C
& C2 to be near the MU drain and ML source nodes.
1
2. Put RT9204 to be near the C
3. Put C
4. Put C
BOOT
VCC
Function Block Diagram
Preliminary
+
C
OUT
1000µF
C
BOOT
BOOT
RT9204
Layout Placement
as close as to BOOT pin
as close as to VCC pin
0.1µF
OUT
L
GS
5µH
Diod e
MU
D
C1
1µF
GND Re tur n
+
RT9204
C2
470µF
VCC
DRV
FBL
FB
GND
LDO
0.8V
Reference
0.8V
Error Amp
++
_
0.5V
+
35dB
Power
on Reset
6.0V
Regulator
BOOT
Soft Start
_
UVP
+
1V
_
OVP
+
_
UVP
+
+
_
SS
+
PWM
_
Control
Logic
UGATE
600kH z
Oscillator
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RT9204
Preliminary
Absolute Maximum Ratings
z
Supply Voltage VCC 7V
z
BOOT & UGATE to GND 15V
z
Input, Output or I/O Voltage GND−0.3V ~ 7V
z
Power Dissipation, PD @ TA = 25°C
SOP-8 0.625W
z
Package Thermal Resistance
SOP-8, θ
z
Ambient Temperature Range 0°C ~ +70°C
z
Junction Temperature Range -40°C ~ +125°C
z
Storage Temperature Range -65°C ~ +150°C
z
Lead Temperature (Soldering, 10 sec.) 260°C
JA
160°C/W
CAUTION:
Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the
device. This is a stress only rating and operation of the device at these or any other conditions above those
indicated in the operational sections of this specification is not implied.
Electrical Characteristics
(V
= 5V, TA = 25°C, Unless otherwise specified.)
CC
Parameter Symbol Test Conditions Min Typ Max Units
VCC Supply Current
Nominal Supply Current
VCC Regulated Voltage
I
V
CC
CC
UGATE, LGATE open -- 3 -- mA
BOOT=
V
12V -- 6 -- V
Power-On Reset
Rising VCC Threshold 3.75 4.1 4.35 V
VCC Threshold Hysteresis -- 0.5 -- V
Reference
Reference Voltage Both FB & FBL 0.784 0.8 0.816 V
Oscillator
Free Running Frequency 550 600 650 KHz
Ramp Amplitude
∆ V
OSC
-- 1.75 --
V
PWM Error Amplifier
DC Gain -- 35 -- dB
PWM Controller Gate Driver
Upper Drive Source
Upper Drive Sink
R
UGATEVBOOT
R
UGATEVUGATE
= 12V; V
= 1V
BOOT
- V
UGATE
= 1V
-- 7 --
-- 5 --
Linear Regulator
DRV Driver Source
V
DRV
= 2V
100 -- -- mA
Protection
FB Over-Voltage Trip FB Rising -- 1 -- V
FB & FBL Under-Voltage Trip FB & FBL Falling -- 0.5 -- V
Soft-Start Interval -- 1 -- mS
SD Pin Threshold VCC = 5V -- 1.5 -- V
SD pin Sink Current VCC = 5V -- 40 --
P-P
Ω
Ω
µA
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Typical Operating Charateristics
Preliminary
RT9204
VCC = 5V
V
= 2.2V
OUT
Power On
Time
Load Transient
UGATE
V
V
V
CC
OUT1
OUT2
V
V
V
CC
OUT1
OUT2
Power Off
Time
Load Transient
UGATE
VCC = 5V
V
OUT
= 2.2V
V
V
OUT
OUT
Time
Short Hiccup
V
= 5V
CC
V
OUT
C
OUT
VCC = 5V
V
OUT
= 2.2V
= 3000µF
= 2.2V
UGATE
Reference (V)
0.803
0.802
0.801
0.800
0.799
0.798
0.797
V
OUT
= 5V
V
CC
V
OUT
C
OUT
Time
Reference vs. Temperature
= 2.2V
= 3000µF
0.796
Time
-50 0 50 100 150
Temperature ( C)
°
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RT9204
Preliminary
POR (Rising/Falling) vs. Temperature
4.3
4.2
4.1
4.0
3.9
POR (V)
3.8
Rising
Falling
3.7
3.6
-50 0 50 100 150
Temperature ( C)
°
Oscillator Frequency vs. Temperature
315
630
310
620
305
610
300
600
295
590
290
580
285
570
Frequency (kHz)
280
560
275
550
540
270
-50 0 50 100 150
Temperature ( C)
°
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Preliminary
Functional Pin Description
GND (Pin 1)
Signal and power ground for the IC. All voltage levels
are measured with respect to this pin.
VCC (Pin 2)
This is the main bias supply for the RT9204. This pin
also provides the gate bias charge for the lower
MOSFETs gate. The voltage at this pin monitored for
power-on reset (POR) purpose. This pin is also the
internal 6.0V regulator output powered from BOOT pin
when BOOT pin is directly powered from ATX 12V.
DRV (Pin 3)
This pin is linear regulator output driver. Connect to
external bypass NPN transistor base or NMOSFET
gate terminal.
FBL (Pin 4)
This pin is connected to the linear regulator output
divider. This pin also connects to internal linear
regulator error amplifier inverting input and protection
monitor.
RT9204
FB (Pin 5)
This pin is connected to the PWM converter’s output
divider. This pin also connects to internal PWM error
amplifier inverting input and protection monitor.
SD (Pin 6)
Active low design with a 40µA pull low current source.
Pull this pin to VCC to shutdown both PWM and linear
regulator.
BOOT (Pin 7)
This pin provides ground referenced bias voltage to
the upper MOSFET driver. A bootstrap circuit is used
to create a voltage suitable to drive a logic-level N-
channel MOSFET when operating at a single 5V
power supply. This pin also could be powered from
ATX 12V, in this situation, an internal 6.0V regulator
will supply to VCC pin for internal voltage bias.
UGATE (Pin 8)
Connect UGATE pin to the PWM converter’s upper
MOSFET gate. This pin provides the gate drive for the
upper MOSFET.
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RT9204
Functional Description
Preliminary
The RT9204 operates at either single 5V power
supply with a bootstrap UGATE driver or 5V/12V
dual-power supply form the ATX SMPS. The dual-
power supply is recommended for high current
application, the RT9204 can deliver higher gate
driving current while operating with ATX SMPS based
on dual-power supply.
The Bootstrap Operation
In a single power supply system, the UGATE driver of
RT9204 is powered by an external bootstrap circuit,
as the Fig.1. The boot capacitor, C
, generates a
BOOT
floating reference at the PHASE node. Typically a
0.1µF C
is enough for most of MOSFETs used
BOOT
with the RT9204. The voltage drop between BOOT
and PHASE node is refreshed to a voltage of VCC –
diode drop (V
) while the low side MOSFET turning
D
on.
R1
0.1µF
D1
+
PHASE
C2
1µF
VCC
RT9204
BOOT
UGATE
5V
C1
1µF
R1
10
12V
VCC
C2
1µF
6.0 V
Regulator
RT9204
BOOT
UGATE
Fig.2 Dual Power Supply Operation
Power On Reset
The Power-On Reset (POR) monitors the supply
voltage (normal +5V) at the VCC pin and the input
voltage at the OCSET pin. The VCC POR level is
4.1V with 0.5V hysteresis and the normal level at
OCSET pin is 1.5V (see over-current protection). The
POR function initiates soft-start operation after all
supply voltages exceed their POR thresholds.
Soft Start
A built-in soft-start is used to prevent surge current
from power supply input during power on. The soft-
start voltage is controlled by an internal digital
counter. It clamps the ramping of reference voltage at
the input of error amplifier and the pulse-width of the
output driver slowly. The typical soft-start duration is
2mS.
5V
+
Fig.1 Single 5V power Supply Operation
Under Voltage and Over Voltage Protection
The voltage at FB pin is monitored and protected
Dual Power Operation
The RT9204 was designed to regulate a 6.0V at VCC
pin automatically when BOOT pin is powered by 12V.
In a system with ATX 5V/12V power supply, the
RT9204 is ideal for higher current application due to
the higher gate driving capability, V
UGATE
= 7V. A RC
(10Ω/1µF) filter is also recommended at BOOT pin to
against OC (over current), UV (under voltage), and
OV (over voltage). The UV threshold is 0.5V and OV-
threshold is 1.0V. Both UV/OV detection have 30µS
triggered delay. When OC or UV trigged, a hiccup re-
start sequence will be initialized, as shown in Fig.3.
Only 3 times of trigger are allowed to latch off. Hiccup
is disabled during soft-start interval.
prevent the ringing induced from fast power on, as
shown in Fig.2.
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Preliminary
RT9204
COUNT = 1 COUNT = 2 COUNT = 3
4V
SS
2V
Internal
0V
OVERLOAD
APPLIED
FB or FBL Voltage
T0T1 T2
TIME
T3
Fig. 3
Applications Information
Inductor Selection
The RT9204 was designed for V
application mainly. Fig.4 shows the typical topology
and waveforms of step-down converter.
The ripple current of inductor can be calculated as
follows:
IL
RIPPLE
= (5V - V
OUT
)/L × T
Because operation frequency is fixed at 600kHz,
T
ON
The V
V
OUT RIPPLE
= 3.33 × V
ripple is
OUT
= IL
OUT
RIPPLE
/5V
× ESR
ESR is COUT capacitor equivalent series resistor
= 5V, step-down
IN
ON
Shutdown
Pulling high the SD pin by a small single transistor
can shutdown the RT9204 PWM controller as shown
in typical application circuit. Normally SD pin can be
floating because an internal 40µA current source will
pull low the SD shutdown pin voltage.
Q
V
I
C.C.M.
L
V
L
DC
T
S
V
R
O
Table 1
T
ONTOFF
V
V
L
i
L
I - VO
I
µ
-
VO
Q
µ
IL = I
O
L
Table 1 shows the ripple voltage of V
*Refer to Sanyo low ESR series (CE, DX, PX…)
: VIN = 5V
OUT
i
Q
I
Q
The suggested L and C are as follows:
i
2µH with ≥ 1500µF C
5µH with ≥ 1000µF C
OUT
OUT
D
I
D
Fig.4
V
OUT
3.3V 2.5V 1.5V
Inductor 2µH5µH2µH5µH2µH5µH
1000µF (ESR = 53mΩ) 100mV 40mV 110mV 44mV 93mV 37mV
1500µF (ESR = 33mΩ) 62mV 25mV 68mV 28mV 58mV 23mV
3000µF (ESR = 21mΩ) 40mV 16mV 43mV 18mV 37mV 15mV
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RT9204
Preliminary
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.
V
BOOT
= 12V
6V
DRV
BOOT
VCC
RT9204
FBL
R3
R4
V
OUT2
+
R4 < 1K
≤ 3.3 V
The output capacitors are necessary for filtering
output and stabilizing the close loop (see the PWM
loop stability). For powering advanced, high-speed
processors, it is required to meet with the
requirement of fast load transient, high frequency
capacitors with low ESR/ESL capacitors are
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
as setting voltage. When driving
OUT2
+VT+gate-drive voltage to
OUT2
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
BOOT
= 12V operation condition as Fig. 6, VCC is regulated
as higher to 6V providing more gate-drive for pass
MOSFET transistor, V
can be set as ≤ 3.3V.
OUT2
Fig. 6
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:
DC loop gain G
LC filter pole P
O
Error Amp pole P
ESR zero Z
= × π × ESR × C
O
= 35dB × ×
A
1
= × π ×
2
= 300kHz
A
1
2
5
6.1
LC
8.0
VOUT
The RT9204 Bode plot as shown Fig.7 is stable in
most of application conditions.
= 3.3V
V
OU T
C
= 1500µF(33mΩ)
OUT
L=2µH
= 2.9kHz
40
30
= 2.5V
V
OU T
= 3.3V
V
OU T
= 1.5V
V
OU T
P
O
= 3.2kHz
Z
O
20
10
Loop Gain
VCC = 5V
DRV
BOOT
VCC
RT9204
FBL
R3
R4
V
OUT2
+
R4 < 1K
≤ 2.5 V
Fig. 7
Fig. 5
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1M100k10k1k100
Preliminary
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.
FB (V)
0.8 2
0.8 1
0.8
0.7 9
0.8 8
IN
FB
0.5
& V
setting. The FB reference voltage of
OUT
= 5V & V
IN
= 5V application, the FB
IN
voltage can be calculated
OUT
I3
+
_
I2
1K
REP
0.8V
_
EA
+
1.75 V
56K
RAMP
+
PWM
OUT
_
Fig. 8
VIN = 5 V
V
(V)
OUT
Fig. 9
= 2.5V
43.531 1.5 2 2.5
4.5
RT9204
VIN
L
V
+
C
OUT
1R
1(V8.0V
)
1OU T
2OUT
+×=
2R
3R
1(V8.0V
+×=
)
4R
PWM Layout Considerations
MOSFETs switch very fast and efficiently. The speed
with which the current transitions from one device to
another causes voltage spikes across the
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.
OUT1
C1
R1
R2
R2 < 1K
Fig. 10
DRV
RT9204
FBL
FB
R3
R4
R4 < 1K
+
V
OUT2
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11
RT9204
Preliminary
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
output inductor and output capacitors between the
MOSFETs and the load. Also locate the PWM
controller near by MOSFETs.
A multi-layer printed circuit board is recommended.
Fig.11 shows the connections of the critical
components in the converter. Note that the capacitors
CIN and COUT each of them represents numerous
physical capacitors. Use a dedicated grounding plane
and use vias to ground all critical components to this
layer. Apply another solid layer as a power plane and
cut this plane into smaller islands of common voltage
levels. The power plane should support the input
power and output power nodes. Use copper filled
polygons on the top and bottom circuit layers for the
PHASE node, but it is not necessary to oversize this
particular island. Since the PHASE node is subjected
to very high dV/dt voltages, the stray capacitance
formed between these island and the surrounding
circuitry will tend to couple switching noise. Use the
remaining printed circuit layers for small signal
routing. The PCB traces between the PWM controller
and the gate of MOSFET and also the traces
connecting source of MOSFETs should be sized to
carry 2A peak currents.
GND
5V
IQ1
PHASE
Q1
+
UGATE
IL
IQ2
VCC GND
RT9204
FB
V
OUT
+
+
LOAD
Fig. 11
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Package Information
B
J
A
Preliminary
H
M
F
C
RT9204
D
Dimensions In Millimeters Dimensions In Inches
Symbol
Min Max Min Max
A 4.801 5.004 0.189 0.197
B 3.810 3.988 0.150 0.157
C 1.346 1.753 0.053 0.069
D 0.330 0.508 0.013 0.020
F 1.194 1.346 0.047 0.053
H 0.178 0.254 0.007 0.010
I 0.102 0.254 0.004 0.010
J 5.791 6.198 0.228 0.244
M 0.406 1.270 0.016 0.050
I
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13
RT9204
Preliminary
RICHTEK TECHNOLOGY CORP.
Headquarter
6F, No. 35, Hsintai Road, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5510047 Fax: (8863)5537749
www.richtek-ic.com.tw DS9204-00 February 2002
14
RICHTEK TECHNOLOGY CORP.
Taipei Office (Marketing)
8F-1, No. 137, Lane 235, Paochiao Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8862)89191466 Fax: (8862)89191465
Email: marketing@richtek-ic.com.tw
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