RT9209 [RICHTEK]
Synchronous Buck PWM DC-DC with Enable & PGOOD; 同步降压PWM DC -DC带使能和PGOOD
| 型号： | RT9209 |
| 厂家： | 
RICHTEK TECHNOLOGY CORPORATION |
| 描述： | Synchronous Buck PWM DC-DC with Enable & PGOOD |
| 文件： | 总14页 (文件大小：207K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
RT9209/A
Synchronous Buck PWM DC-DC with Enable & PGOOD
General Description
Features
z Operates at 5V
The RT9209/A is a single power supply PWM DC-DC
converter controller designed to drive N-MOSFET in a
synchronous buck topology. The IC integrates the control,
output adjustment, monitoring and protection functions into
a small 8-pin package.
z 0.8V Internal Reference
z Drives Two N-MOSFET
z Voltage Mode PWM Control
z Fast Transient Response
z Fixed 260kHz/400kHz Oscillator Frequency
z Dynamic 0 to 100% Duty Cycle
The RT9209/Auses an 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 260kHz/
400kHz oscillator reduce the component size for saving
board area.
z Internal PWM Loop Compensation
z Internal Soft-Start
z Adaptive Non-Overlapping Gate Driver
z Over-Voltage Protection Uses Lower MOSFET
z RoHS Compliant and 100% Lead (Pb)-Free
The RT9209/A future a enable control pin to shutdown PWM
switching and a 90% power good flag indicator. The FB
pin under voltage detection function monitor the output
short circuit which trigger a three time hiccup sequence
to latch off the chip function.
Applications
z Motherboard Power Regulation for Computers
z Subsystems Power Supplies
z Cable Modems, Set Top Box, and DSL Modems
z DSP and Core Communications processor Supplies
z Memory Power Supplies
Ordering Information
RT9209/A
z Personal Computer Peripherals
z Industrial Power Supplies
Package Type
S : SOP-8
z 5V-InputDC-DC Regulators
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
z Low VoltageDistributed Power Supplies
Pin Configurations
400kHz
260kHz
(TOP VIEW)
SS
8
7
6
5
FB
VCC
Note :
2
3
4
PGOOD
BOOT
UGATE
RichTek Pb-free and Green products are :
`RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
LGATE
GND
SOP-8
`Suitable for use in SnPb or Pb-free soldering processes.
`100%matte tin (Sn) plating.
DS9209/A-08 March 2007
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1
RT9209/A
Typical Application Circuit
5V
R1
R2
120
250
R3
10K
PGOOD
C1
1
8
7
6
5
470uF
FB
SS
D1
C2
0.1uF
2
3
4
MU
ML
VCC PGOOD
C
BOOT
L1
C3
1uF
LGATE
BOOT
VOUT
A
5uH
0.1uF
GND
UGATE
RT9209/A
C4
1000uF
Figure A. RT9209/A Booted from 5V
5V
R2
R1
120
250
R4
10K
PGOOD
C1
470uF
1
2
3
4
8
FB
SS
C2
7
6
5
MU
ML
VCC PGOOD
0.1uF
L1
C3
1uF
LGATE
BOOT
VOUT
A
5uH
GND
UGATE
RT9209/A
C4
1000uF
R3
10
12V
C5
1uF
Figure B. RT9209/A Booted from 12V
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DS9209/A-08 March 2007
2
RT9209/A
MU
D
C
OUT
1000uF
L
G
S
5uH
C
C
IN2
IN1
GND
VCC
1uF
470uF
C
C
BOOT
VCC
Diode
1uF
BOOT
RT9209/A
0.1uF
GND Return
Layout Placement
Layout Notes
1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes.
2. Put RT9209/A to be near the COUT
3. Put CBOOT as close as to BOOT pin
4. Put CVCC as close as to VCC pin
Function Block Diagram
6.5V
Regulation
VCC
BOOT
Power on
Reset
PGOOD
+
-
SS
PGOOD
Soft Start
0.72V
0.8
Reference
1V
-
OVP
+
UGATE
-
UVP
0.5V
SS
Control
Logic
+
0.8V
+
+
VCC
PWM
+
FB
-
Error
-
Amplifier
LGATE
PWM Loop
Compensation
260kHz/300kHz
Oscillator
GND
DS9209/A-08 March 2007
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3
RT9209/A
Functional Pin Description
FB (Pin1)
UGATE (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.
Connect UGATE pin to the PWM converter's upper
MOSFET gate. This pin provides the gate drive for the
upper MOSFET.
VCC (Pin 2)
BOOT (Pin 6)
This is the main bias supply for the RT9209/A. 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 6.5V regulator
output powered from BOOT pin when BOOT pin is directly
powered from ATX 12V.
This pin provides ground referenced bias voltage to the
upper MOSFET driver.Abootstrap 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, a internal 6.5V regulator will supply to VCC pin
for internal voltage bias.
LGATE (Pin 3)
PGOOD (Pin 7)
Connect LGATE to the PWM converter's lower MOSFET
gate. This pin provides the gate drive for the lower
MOSFET.
PGOOD is an open collector output used to indicate the
status of the PWM converter output voltage. This pin is
pulled low when the FB is not over 90% of the reference
voltage.
GND (Pin 4)
Signal and power ground for the IC. All voltage levels are
measured with respect to this pin.
SS (Pin 8)
Connect a capacitor from this pin to ground. This capacitor,
along with an internal 22μA current source, sets the soft-
start internal of the synchronous PWM converter.
Absolute Maximum Ratings
z Supply Input Voltage, VCC ------------------------------------------------------------------------------------------- 7V
z BOOT & UGATE toGND--------------------------------------------------------------------------------------------- 19V
z Input, Output or I/O Voltage ----------------------------------------------------------------------------------------- GND-0.3V to 7V
z Power Dissipation, PD @ TA = 25°C
SOP-8 -------------------------------------------------------------------------------------------------------------------- 0.625W
z Package Thermal Resistance
SOP-8, θJA -------------------------------------------------------------------------------------------------------------- 160°C/W
z Ambient Temperature Range---------------------------------------------------------------------------------------- 0°C to +70°C
z Junction Temperature Range---------------------------------------------------------------------------------------- 0°C to +125°C
z Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to +150°C
z Lead Temperature (Soldering, 10 sec.)--------------------------------------------------------------------------- 260°C
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.
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DS9209/A-08 March 2007
RT9209/A
Electrical Characteristics
(VCC = 5V, TA = 25°C, Unless otherwise specified.)
Parameter
Symbol
Test Conditions
Min Typ Max Units
V
Supply Current
CC
Nominal Supply Current
UGATE, LGATE open
--
3
6
mA
I
CC
Power-On Reset
Rising V Threshold
3.7
0.3
4.1
0.5
4.5
0.7
V
V
CC
V
Threshold Hysteresis
CC
Reference
Reference Voltage
Oscillator
0.784 0.8 0.816
V
RT9209
210
350
--
260
400
1.75
310
450
--
Free Running Frequency
kHz
RT9209A
Ramp Amplitude
Error Amplifier
DC gain
Δ V
V
P-P
OSC
33
35
40
dB
PWM Controller Gate Driver
BOOT= 12V
Upper Drive Source
--
7
12
R
UGATE
Ω
BOOT-V
= 1V
UGATE
Upper Drive Sink
--
--
--
7
7
3
7.5
6
R
UGATE
R
LGATE
R
LGATE
V
= 1V
Ω
Ω
Ω
UGATE
Lower Drive Source
Lower Drive Sink
V
CC
V
LGATE
- V
= 1V,
LGATE
4
= 1V
Protection
FB Over-Voltage Trip
FB Under-Voltage Trip
Power Good Threshold
Power Good Hysteresis
Power Good Sink Capability
SS Source Current
FB Rising
--
--
1
0.6
90
2
--
--
V
V
FB Falling
FB pin Rising
86
--
95
--
%
%
V
--
0.4
32
I
= 1mA
PGOOD
12
20
μA
DS9209/A-08 March 2007
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5
RT9209/A
Typical Operating Characteristics
Dead Time
Dead Time
Booted from 5V
Booted from 5V
UGATE
UGATE
LGATE
LGATE
IOUT = 0A
IOUT = 0A
Time (50ns/Div)
Time (50ns/Div)
Dead Time
Dead Time
Booted from 12V
UGATE
Booted from 12V
LGATE
UGATE
LGATE
IOUT = 0A
IOUT = 0A
Time (50ns/Div)
Time (50ns/Div)
Load Transient
Load Transient
UGATE
UGATE
VOUT
VOUT
VCC = 5V
VCC = 5V
IOUT
VOUT = 2.5V
VOUT = 2.5V
COUT = 1000uF
COUT = 1000uF
IOUT = 10A to 0A
IOUT
IOUT = 0A to 10A
Time (10us/Div)
Time (10us/Div)
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DS9209/A-08 March 2007
RT9209/A
Power On
Power Off
Booted from 5V
IOUT = 10A
Booted from 5V
IOUT = 10A
VCC
CSS = 0.1uF
VCC
VOUT
VOUT
Time (2.5ms/Div)
Time (10ms/Div)
Power On
Power Off
Booted from 12V
IOUT = 10A
Booted from 12V
IOUT = 10A
VCC
VCC
VOUT
VOUT
Time (2.5ms/Div)
Time (50ms/Div)
Boostrap Waveform
Boostrap Waveform
Booted from 5V
UGATE
UGATE
LGATE
LGATE
A node
A node
Booted from 12V,
Time (1us/Div)
Time (1us/Div)
DS9209/A-08 March 2007
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7
RT9209/A
Short Hiccup
Short Hiccup
Booted from 12V
Booted from 5V
UGATE
UGATE
VOUT
VOUT
Time (25ms/Div)
Time (500ms/Div)
PGOOD vs. VOUT
VCC vs. VSS
IOUT = 10A
CSS = 0.1uF
VCC
PGOOD
VSS
VOUT
Time (25ms/Div)
Time (5ms/Div)
Reference vs. Temperature
Oscillator Frequency vs. Temperature
0.808
0.806
0.804
0.802
0.8
410
400
390
380
370
360
350
0.798
0.796
0.794
0.792
0.79
RT9209A
0.788
-35
-15
5
25
45
65
85
105 125
-35
-15
5
25
45
65
85
105 125
(°C)
Temperature
Temperature (°C)
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DS9209/A-08 March 2007
RT9209/A
POR(Rising/Falling) vs. Temperature
4.2
4.1
4
Rising
3.9
3.8
3.7
3.6
3.5
Falling
-35
-15
5
25
45
65
85
105 125
Temperature
(°C)
DS9209/A-08 March 2007
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9
RT9209/A
Application Information
5V
The RT9209/A operates at either single 5V power supply
with a bootstrap UGATE driver or a 5V/12V dual-power
supply form the ATX SMPS. The dual- power supply is
recommended for high current applications, the
RT9209/A can deliver higher gate driving current while
operating withATX SMPS based on a dual-power supply.
R1
10
BOOT
C1
12V
VCC
6.5V
Regulator
5V
1uF
+
UGATE
A
VCC
The Bootstrap Operation
C2
In a single power supply system, the UGATE driver of
RT9209/A is powered by an external bootstrap circuit, as
LGATE
1uF
shown in the Figure1. The boot capacitor, CBOOT
,
RT9209/A
generates a floating reference. Typically a 0.1μF CBOOT
is enough for most of MOSFETs used with the
RT9209/A. The voltage drop between BOOT and A node
is refreshed to a voltage of VCC −diode drop (VD) while the
lower MOSFET turning on.
Figure 2. Dual Power Supply Operation
Power On Reset
The Power-On Reset (POR) monitors the supply voltage
(normal +5V) at the VCC pin. The VCC POR level is set
to 4.1V with 0.5V hysteresis. The POR function initiates
soft-start operation after all supply voltages exceed their
POR thresholds.
VCC
D1
C2
5V
BOOT
1uF
+
-
+
C1
0.1uF
UGATE
Soft Start
A
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 22μA to change a capacitor
slowly. It clamps the ramping of reference voltage at the
input of error amplifier and the pulse-width of the output
driver slowly.
VCC
LGATE
RT9209/A
Under Voltage and Over Voltage Protection
Figure 1. Single 5V power Supply Operation
Dual Power Operation
The voltage at FB pin is monitored and protected against
OC (over current), and OV (over voltage). The UV
threshold is 0.5V and OV-threshold is 1.0V. Both UV/OV
detection have 30ms triggered delay. When OC or UV
trigged, a hiccup re-start sequence will be initialized, as
shown in Figure 3. Only 3 times of trigger are allowed to
latch off. Hiccup is disabled during soft-start interval.
The RT9209/A is designed to supply a regulated 6.5V at
VCC pin automatically when BOOT pin is powered by a
12V. In a system with ATX 5V/12V power supply, the
RT9209/A is ideal for higher current applications due to
the higher gate driving capability, VUGATE = 12V and VLGATE
= 6.5V. A RC (10Ω/1μF) filter is also recommended at
BOOT pin to prevent the ringing induced from fast power-
on, as shown in Figure 2.
Shutdown
Pulling low the SS pin by a small single transistor can
shutdown the RT9209/A PWM controller as shown in
typical application circuit.
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DS9209/A-08 March 2007
RT9209/A
COUNT = 2
COUNT = 3
COUNT = 1
4V
2V
0V
L
Q
R
V
V
D
C
OVERLOAD
APPLIED
I
O
C.C.M.
T
S
0A
T3
T0
T1
T2
TIME
T
T
OFF
ON
Figure 3
V - V
I
O
V
L
Inductor Selection
The RT9209/A was designed for VIN = 5V, step-down
application mainly. Figure 4 shows the typical topology
and waveforms of step-down converter.
- V
O
i
L
uQ
I = I
L
O
The ripple currents of inductor can be calculated as follows:
uI
L
(5V - VOUT)
ILRIPPLE =
× TON
L
Because operation frequency is fixed at 260kHz/400kHz,
i
Q
VOUT
TON = 3.85× VOUT ,or 2.5×
I
Q
5V
5V
The VOUT ripple is
i
D
VOUT RIPPLE =ILRIPPLE ×ESR
I
D
ESR is output capacitor equivalent series resistor
Figure 4
DS9209/A-08 March 2007
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11
RT9209/A
Input / Output Capacitor
Reference Voltage
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.
Because RT9209/A use a low 35dB gain error amplifier,
shown in Figure 6. The voltage regulation is dependent
on VIN & VOUT setting. The FB reference voltage of 0.8V
were trimmed at VIN = 5V & VOUT = 2.5V condition. In a
fixed VIN = 5V application, the FB reference voltage vs.
VOUT voltage can be calculated as Figure 7.
R2
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.
56K
R1
FB
+
-
-
EA
+
1K
+
PWM
-
REF
0.8V
RAMP
1.75V
Figure 6
Another concern is high ESR induced ripple may trigger
UV or OV protections
0.82
VIN = 5V
PWM Loop Stability
0.81
0.80
0.79
The RT9209/A 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 :
0.78
0.5
1
1.5
2
2.5
3
3.5
4
4.5
V
(V)
OUT
5
0.8
Figure 7
DC loop gain GA = 35 dB×
×
1.6 VOUT
Feedback Divider
1
LC filter polePO = ×π × LC
The reference of RT9209/Ais 0.8V. The output voltage can
be set using a resistor based divider as shown in Figure 8.
Put the R1 and R2 as close as possible to FB pin and R2
should less than 1 kΩ to avoid noise coupling.
2
Error Amp polePA = 300kHz
1
ESR zero ZO = ×π ×ESR×C
2
VIN
The RT9209/A Bode plot as shown Figure 5 is stable in
most of application conditions.
L
V
= 3.3V
OUT
A
C
= 1500uF(33mΩ)
V
OUT
OUT
L = 2uH
V
= 1.5V
P
= 2.9kHz
OUT
OUT
O
40
30
20
10
C
V
= 2.5V
OUT
R1
Z
= 3.2kHz
O
V
= 3.3V
OUT
RT9209/A
FB
Loop Gain
R2
100
1k
10k
100k
1M
Figure 8
Figure 5
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DS9209/A-08 March 2007
RT9209/A
PWM Layout Considerations
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.
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 over-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.
IQ1
IL
5V
V
A
OUT
Q1
LOAD
IQ2
C
C
OUT
IN
Q2
GND
VCC
GND
RT9209/A
FB
LGATE
UGATE
Figure 9
There are two sets of critical components in a DC-DC
converter using the RT9209/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 output inductor and output
capacitors between the MOSFETs and the load. Also
locate the PWM controller near by MOSFETs.
Amulti-layer printed circuit board is recommended. Figure
9 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
the remaining printed circuit layers for small signal routing.
DS9209/A-08 March 2007
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13
RT9209/A
Outline Dimension
H
A
M
J
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
B
C
D
F
H
I
4.801
3.810
1.346
0.330
1.194
0.170
0.050
5.791
0.400
5.004
3.988
1.753
0.508
1.346
0.254
0.254
6.200
1.270
0.189
0.150
0.053
0.013
0.047
0.007
0.002
0.228
0.016
0.197
0.157
0.069
0.020
0.053
0.010
0.010
0.244
0.050
J
M
8-Lead SOP Plastic Package
Richtek Technology Corporation
Headquarter
Richtek Technology Corporation
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
8F, No. 137, Lane 235, Paochiao Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)89191466 Fax: (8862)89191465
Email: marketing@richtek.com
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14
DS9209/A-08 March 2007
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