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Preliminary
RT9204/A
Dual Regulators - Standard Buck PWM DC-DC and Linear Controller
General Description
The RT9204/A 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/A uses 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 600kHz oscillator reduce the component size for saving board area. The RT9204/A protects the converter and regulator by monitoring the output under voltage.
Features
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Operate from 5V 0.8V Internal Reference Voltage Mode PWM Control Fast Transient Response Fixed 600kHz Oscillator Frequency Full 0 to 100% Duty Cycle Internal Soft Start Internal PWM Loop Compensation RoHS Compliant and 100% Lead (Pb)-Free
Applications
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Ordering Information
RT9204/A Package Type S : SOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) UVP : Hiccup Mode UVP : Latch Mode Note : RichTek Pb-free and Green products are : }RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. }Suitable for use in SnPb or Pb-free soldering processes. }100%matte tin (Sn) plating.
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Motherboard Power Regulation for Computers Subsystems Power Supplies Cable Modems, Set Top Box, and DSL Modems DSP and Core Communications Processor Supplies Memory Power Supplies Personal Computer Peripherals Industrial Power Supplies 5V-Input DC-DC Regulators Low Voltage Distributed Power Supplies
Pin Configurations
(TOP VIEW)
GND VCC DRV FBL 2 3 4 8 7 6 5 UGATE BOOT SD FB
SOP-8
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RT9204/A
Typical Application Circuit
VAUX 3.3V Q1 2SD1802 VOUT2 1.6V R4 100 R5 100 C5 1uF
+
Preliminary
R1 10 1 2 3 4 GND VCC DRV FBL RT9204/A UGATE BOOT SD FB 8 7 6 5 C3
+
5V BAT54A
0.1uF VOUT1 2.5V R3
+
L1 5uH C4 1000uF
MU D1 SS34
C2 1uF
C1 470uF
C6 220uF
250 R2 120 C7 10nF
Figure1. RT9204/A powered from 5V only
5V
R1 0 VAUX 3.3V Q1 Suggest use Transistor 2SD5706 VOUT2 1.6V R4 100 R5 100
+
C7 1uF 1 2 3 4 8 7
R6 C5 1uF GND VCC DRV FBL RT9204/A UGATE BOOT SD FB 10 12V 5V
+
6 5
VOUT1 2.5V R3
+
L1 5uH C4 1000uF
MU D1 SS34
C2 1uF
C1 470uF
C6 220uF
250 R2 120 C7 10nF
Figure2. RT9204/A powered from 12V
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Preliminary
MU COUT 1000uF GND CVCC 1uF CBOOT VCC BOOT 0.1uF RT9203/A GND Return Diode D L 5uH G S
+ +
RT9204/A
CIN1 1uF
C IN2 470uF
Layout Placement
Layout Notes 1. Put C1 & C2 to be near the MU drain and ML source nodes. 2. Put RT9204/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
6.0V Regulation Power on Reset DRV FBL 0.8 Reference + 1V +
OVP UVP LDO
VCC
BOOT
+ -
0.8V FB
+ 35dB Error Amplifier
GND
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+
Soft Start
0.5V +UVP + +PWM -
Control Logic
UGATE
SS
600kHz Oscillator
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RT9204/A
Functional Pin Description
GND (Pin 1)
Preliminary
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/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 6.0V 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. 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 40A 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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Preliminary Absolute Maximum Ratings
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RT9204/A
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Supply Voltage VCC ------------------------------------------------------------------------------------------------ 7V BOOT & UGATE to GND ------------------------------------------------------------------------------------------- 15V Input, Output or I/O Voltage --------------------------------------------------------------------------------------- GND-0.3V to 7V Power Dissipation, PD @ TA = 25C SOP-8 ------------------------------------------------------------------------------------------------------------------ 0.625W Package Thermal Resistance SOP-8, JA ------------------------------------------------------------------------------------------------------------------------------------------------------- 160 C/W Ambient Temperature Range -------------------------------------------------------------------------------------- 0 C to +70C Junction Temperature Range -------------------------------------------------------------------------------------- -40C to +125C Storage Temperature Range --------------------------------------------------------------------------------------- -65C to +150C Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------- 260C
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
(VCC = 5V, TA = 25 C, Unless otherwise specified.)
Parameter VCC Supply Current Nominal Supply Current VCC Regulated Voltage Power-On Reset Rising VCC Threshold VCC Threshold Hysteresis Reference Reference Voltage Oscillator Free Running Frequency Ramp Amplitude PWM Error Amplifier DC Gain PWM Controller Gate Driver Upper Drive Source Upper Drive Sink Linear Regulator DRV Driver Source
Symbol
Test Conditions
Min
Typ
Max
Units
ICC VCC
UGATE, LGATE open VBOOT=12V
---
3 6
---
mA V
3.75 -Both FB & FBL 0.784 550 VOSC --
4.1 0.5 0.8 600 1.75
4.35 -0.816 650 --
V V V kHz VP-P
-RUGATE RUGATE VBOOT = 12V; VBOOT - VUGATE = 1V VUGATE = 1V ---
35 7 5
----
dB
VDRV = 2V
100
--
--
mA
To be continued
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RT9204/A
Parameter Protection FB Over-Voltage Trip FB & FBL Under-Voltage Trip Soft-Start Interval SD Pin Threshold SD pin Sink Current Symbol
Preliminary
Test Conditions Min Typ Max Units
FB Rising FB & FBL Falling VCC = 5V VCC = 5V
------
1 0.5 1 1.5 40
------
V V ms V A
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Preliminary Typical Operating Characteristics
Power On
VCC = 5V VOUT = 2.2V VCC VCC
RT9204/A
Power Off
VCC = 5V
VOUT1
VOUT1
VOUT2
VOUT2
Time (1ms/Div)
Time (50ms/Div)
Load Transient
UGATE
Load Transient
UGATE
VOUT VOUT VCC = 5V VOUT = 2.2V COUT = 3000uF VCC = 5V VOUT = 2.2V COUT = 3000uF
Time (5us/Div)
Time (5us/Div)
Short Hiccup (Latch Mode)
VCC = 5V VOUT = 2.2V VCC = 5V VOUT = 2.2V
Short Hiccup
VOUT
VOUT
UGATE
UGATE RT9204 RT9204A
Time (5ms/Div)
Time (2ms/Div)
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RT9204/A
Reference vs. Temperature
0.803 0.802 0.801
Preliminary
POR (Rising/Falling) vs. Temperature
4.3 4.2 4.1 Rising
Reference (V)
POR (V)
0.800 0.799 0.798 0.797 0.796 -50 0 50 100 150
4.0 3.9 3.8 3.7 3.6 -50 0 50 100 150 Falling
Temperature (C)
Temperature (C)
Oscillator Frequency vs. Temperature
315 310
Frequency (kHz) A
305 300 295 290 285 280 275 270 -50 0 50 100 150
Temperature (C)
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Preliminary Application Information
The RT9204/A 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/A 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/A is powered by an external bootstrap circuit, as the Figure 3. The boot capacitor, CBOOT , generates a floating reference at the PHASE node. Typically a 0.1F CBOOT is enough for most of MOSFETs used with the RT9204/A. The voltage drop between BOOT and PHASE node is refreshed to a voltage of VCC-diode drop (VD) while the low side MOSFET turning on.
R1 VCC C2 1uF D1 5V 0.1uF
+
6.0V Regulation BOOT
RT9204/A
VCC
R 12V C 1uF 10 5V
+
UGATE
C2 1uF
RT9204/A
Figure 4. 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. Under Voltage and Over Voltage Protection
BOOT
UGATE
PHASE RT9204/A
Figure 3. Single 5V power Supply Operation Dual Power Operation The RT9204/A 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, VUGATE = 7V. A RC (10/1F) filter is also recommended at BOOT pin to prevent the ringing induced from fast power on, as shown in Figure 4. The voltage at FB pin is monitored and protected 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 30s triggered delay. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Figure 5. For RT9204, only 3 times of trigger are allowed to latch off. But for RT9204A, UVP will be kept hiccup mode. Hiccup is disabled during soft-start interval.
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RT9204/A
COUNT = 1
Internal SS
Preliminary
Shutdown
COUNT = 2 COUNT = 3
4V 2V 0V OVERLOAD APPLIED
FB or FBL Voltage
Pulling high the SD pin by a small single transistor can shutdown the RT9204/A PWM controller as shown in typical application circuit. Normally SD pin can be floating because an internal 40A current source will pull low the SD shutdown pin voltage.
Q L
VI T0T1 T2 TIME T3
D
C
R
VO
Figure 5 Inductor Selection The RT9204/A was designed for VIN = 5V, step-down application mainly. Figure 6 shows the typical topology and waveforms of step-down converter. The ripple current of inductor can be calculated as follows:
ILRIPPLE = (5V - VOUT) L x TON
iL VL
C.C.M. TS
Table 1 TON TOFF VI - VO
- VO uQ uIL
Because operation frequency is fixed at 600kHz, TON = 3.33 x VOUT 5V
iQ
IL = IO
The VOUT ripple is
VOUT
RIPPLE = ILRIPPLE x ESR
IQ
ESR is COUT capacitor equivalent series resistor Table 1 shows the ripple voltage of VOUT : VIN = 5V *Refer to Sanyo low ESR series (CE, DX, PX......) The suggested L and C are as follows: 2H with 1500F COUT 5H with 1000F COUT
VOUT Inductor 1000F (ESR = 53m) 1500F (ESR = 33m) 3000F (ESR = 21m) 2H 100mV 62mV 40mV 3.3V 5H 40mV 25mV 16mV 2H 110mV 68mV 43mV 2.5V 5H 44mV 28mV 18mV 2H 93mV 58mV 37mV 1.5V 5H 37mV 23mV 15mV
iD ID
Figure 6
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DS9204/A-08 March 2007
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 manuf acturer 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, 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/A was designed to drive bipolar NPN or MOSFET pass transistor. For MOSFET pass transistor, normally DRV need to provide minimum VOUT2+VT+gate-drive voltage to keep VOUT2 as setting voltage. When driving MOSFET operating at 5V power supply system, the gate-drive will be limited at 5V. In this situation shown in Figure 5, low VT threshold MOSFET (VT = 1V) and Vout2 setting below 2.5V were suggested. In VBOOT = 12V operation condition as Figure 8, VCC is regulated as higher to 6V providing more gate-drive for pass MOSFET transistor, VOUT2 can be set as 3.3V.
RT9204/A
VOUT2 < 3.3V
+
DRV VBOOT = 12V BOOT 6V FBL R4 VCC RT9204/A R3
R4<1K
Figure 8 PWM Loop Stability The RT9204/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: DC loop gain GA = 35 dB x LC filter pole PO = 1 2 LC 1 2 ESR x C 5 1.6 x 0.8 VOUT
Error Amp pole PA = 300kHz ESR zero ZO =
The RT9204/A Bode plot as shown Figure 9. is stable in most of application conditions.
VOUT = 3.3V
VOUT2 < 2.5V
+
DRV R3 BOOT FBL R4
40 30
COUT = 1500uF(33m) L = 2uH VOUT = 1.5V PO = 2.9kHz VOUT = 2.5V ZO = 3.2kHz VOUT = 3.3V
VCC VCC = 5V RT9204/A
R4<1K
20 Loop Gain 10
100
1k
10k
100k
1M
Figure 7
Figure 9
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RT9204/A
Reference Voltage
Preliminary
VIN
Because RT9204/A use a low 35dB gain error amplifier, shown in Figure 10. 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 11.
L VOUT1 DRV R1 R1 VOUT1 = 0.8V (1+ R2 ) R2 <1K C1 RT9204/A FB FBL R3 R4 R4<1K VOUT2
+ +
COUT
I3 FB + I2 1K REP 0.8V 56K EA + RAMP 1.75V
R3 VOUT2 = 0.8V (1+ R4 )
Figure 12
+ PWM
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/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.
Figure 10
0.82 VIN = 5V 0.81
FB (V)
0.80 0.79 0.78 0.5
1
1.5
2
2.5 3 VOUT (V)
3.5
4
4.5
Figure 11 Feedback Divider The reference of RT9204/A is 0.8V. Both the PWM and LDO output voltages can be set using a resistor based divider as shown in Figure 12. Put the R1&R2 and R3&R4 as close as possible to FB pin and R2&R4 should be less than 1 k 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 ~ 0.1F is enough for C1.
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DS9204/A-08 March 2007
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. Figure 13. 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.
IQ1
RT9204/A
IL VOUT Q1 IQ2
+
5V
+
+
LOAD
GND
VCC UGATE
GND
RT9204/A FB
Figure 13
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RT9204/A
Outline Dimension
Preliminary
A
H M
J
B
F
C I D
Dimensions In Millimeters Symbol Min A B C D F H I J M 4.801 3.810 1.346 0.330 1.194 0.170 0.050 5.791 0.400 Max 5.004 3.988 1.753 0.508 1.346 0.254 0.254 6.200 1.270
Dimensions In Inches Min 0.189 0.150 0.053 0.013 0.047 0.007 0.002 0.228 0.016 Max 0.197 0.157 0.069 0.020 0.053 0.010 0.010 0.244 0.050
8-Lead SOP Plastic Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
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DS9204/A-08 March 2007

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