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Preliminary
RT9203/A
Dual Regulators - Synchronous Buck PWM DC-DC and Linear Controller
General Description
The RT9203/A is a dual-output power controllers designed for high performance graphics cards and personal computers. The IC integrates a synchronous buck controller, a linear controller and protection functions into a small 8-pin package. The RT9203/A uses an internal compensated voltage mode PWM control for simplying design. An internal 0.8V reference allows the output voltage to be precisely regulated to meet low output voltage requirement. A fixed 300kHz oscillation frequency reduces the component size for saving board area. The RT9203/A also features over voltage protection (OVP) and under voltage lock-out (UVLO).
Features
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Operates at 5V 0.8V Internal Reference Drives Two N-MOSFET Voltage Mode PWM Control Fast Transient Response Fixed 300kHz Oscillator Frequency Dynamic 0 to 100% Duty Cycle Internal PWM Loop Compensation Internal Soft-Start Adaptive Non-Overlapping Gate Driver Over-Voltage Protection Uses Lower MOSFET RoHS Compliant and 100% Lead (Pb)-Free
Applications
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Ordering Information
RT9203/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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PC Motherboard 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 Graphic Cards
Pin Configurations
(TOP VIEW)
BOOT UGATE GND LGATE 2 3 4 8 7 6 5 FB FBL DRV VCC
SOP-8
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RT9203/A
5V 5V
Typical Application Circuit
5V
+ 1uF 1N5819 5 + VCC 6 PHASE UGATE 4 8 1uF D2 5 Phase 2 2 G1 3 S2 4 G2 D1 7 D2 6 1uF BOOT 1 680uF 5uH Phase PHKD6N02LT 0.1uF 8 1 S1 D1
100uF
1uH Be Careful during Layout
2SD1802
VOUT1 1.6V
VOUT2 FBL FB RT9203/A GND 120 <1K 3 200 200 10nF LGATE
+
0.8V 7
+
Preliminary
3.4V VOUT2 = 0.8V*(1+R1/R2)
390
680uF LESR
680uF LESR
+
10nF
Figure 1. RT9203/A powered from 5V
VOUT1 = 0.8V*(1+R3/R4)
1uF
470uF
Pull FB trace out after COUT
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DS9203/A-10 March 2007
5V 12V 10 0 0.1uF Phas e + + 1 S1 470uF 470uF D1 7 D2 6 D2 5 Phas e D1 2 2 G1 3 S2 4 G2 4 8 1uF 8 Be Careful during Layout 1uH 5V 5 VCC 1 BOOT 1uF 5uH + + UGATE LGATE FB RT9203/A GND 3 200 200 10nF VOUT1 = 0.8V*(1+R3/R4) PHASE VOUT1 1.6V FBL
3.3V
+
100uF
1uF
6
2SD5706
Suggest use Transistor
VOUT2
0.8V 7
Preliminary
2.5V VOUT2 = 0.8V*(1+R1/R2)
255
510uF 4V OSCON 14mOhm Pull FB trace out after COUT
+
10nF
Figure 2. RT9203/A powered from 12V
1uF
330uF
120 <1K
RT9203/A
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RT9203/A
+
Preliminary
MU COUT 1000uF D L 5uH G S
+
GND CVCC 1uF CBOOT VCC BOOT 0.1uF RT9203/A G S ML D
C1 1uF
C2 470uF
GND Return
Layout Placement
Layout Notes 1. Put C1 & C2 to be near the MU drain and ML source nodes. 2. Put RT9203/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 VCC
LDO
VCC Power on Reset
BOOT
FBL 0.8 Reference + 1V +
OVP UVP
0.8V FB Error
+ SS Error Amplifier
GND
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+ -
DRV
+
Soft Start
UGATE
UVP 0.5V + + +PWM -
Control Logic VCC LGATE
300kHz Oscillator
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Preliminary Functional Pin Description
BOOT (Pin 1) This pin provides ground referenced bias voltage to the upper MOSFET driver. A bootstrap circuit is used to create a voltage that is suitable for driving a logic-level N-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 generating bias required inside the IC. UGATE (Pin 2) Connect the UGATE pin to the gate of upper MOSFET. This pin provides the gate drive for the upper MOSFET. GND (Pin 3) Signal and power ground for the IC. All voltage levels are measured with respect to this pin. LGATE (Pin 4) Connect the LGATE pin to the gate of lower MOSFET. This pin provides the gate drive for the lower MOSFET. VCC (Pin 5) This is the main bias supply for the RT9203/A. This pin also provides the gate bias charge for the gate of lower MOSFET. The voltage at this pin is monitored for ensuring a proper power-on reset (POR). This pin is also the out of an internal 6.0V regulator that powered from the BOOT pin when the BOOT pin is directly powered from ATX 12V. DRV (Pin 6) This pin is the output of a linear controller. It should be connected to the base of an external bypass NPN transistor or the gate of a N-MOSFET to form a linear low dropout regulator. FBL (Pin 7) This pin is connected to the output resistor-divider of an external power transistor or a N-MOSFET based low dropout regulator for regulating and monitoring the output voltage. This pin is also connected to the protection monitor and the invertering input of error amplifier of internal linear regulator inside the IC. FB (Pin 8)
RT9203/A
This pin is connected to the PWM converter's output-divider for regulating and monitoring the output voltage of buck converter. This pin also connects to the protection monitor and the inverting input of internal PWM error amplifier inside the IC.
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RT9203/A
Absolute Maximum Ratings
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Preliminary
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Supply Voltage VCC ------------------------------------------------------------------------------------------------ 7V BOOT & UGATE to GND ------------------------------------------------------------------------------------------- 19V 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 Lower Drive Source Lower Drive Sink Linear Regulator DRV Driver Source
Symbol I CC V CC
Test Conditions UGATE, LGATE open VBOOT = 12V
Min -5.0 3.8 --
Typ 3 6.0 4.1 0.5 0.8 300 1.75 35
Max -7.0 4.4 -0.816 350 -38
Units mA V V V V kHz VP-P dB
V FB
Both PWM and linear regulator
0.784 250
VOSC
-32 BOOT = 12V BOOT-VUGATE = 1V VUGATE = 1V VCC - VLGATE = 1V VLGATE = 1V VDRV = 2V
R UGATE RUGATE R LGATE RLGATE
----100
7.5 5 3.5 2 --
11 8 6 5 --
mA
To be continued
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Preliminary
Parameter Protection FB Over-Voltage Trip FB & FBL Under-Voltage Trip Soft-Start Interval FB Rising FB & FBL Falling 0.9 --Symbol Test Conditions Min
RT9203/A
Typ 1 0.5 2.5 Max -0.65 -Units V V ms
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RT9203/A
Dead Time
Preliminary
Typical Operating Characteristics
Dead Time
VCC = 5V UGATE VCC = 5V UGATE
LGATE
LGATE
Time (50ns/Div)
Time (50ns/Div)
Power On
VCC = 5V VOUT1 = 2.5V VOUT2 = 1.8V VCC VCC
Power On
VCC = 5V VOUT1 = 2.5V VOUT2 = 1.8V
VOUT1
VOUT1
VOUT2
VOUT2
Time (2.5ms/Div)
Time (50ms/Div)
Load Transient
UGATE
Load Transient
UGATE
VOUT VCC = 5V VOUT = 2.2V COUT = 3000uF
VCC = 5V VOUT = 2.2V COUT = 3000uF VOUT
Time (5us/Div)
Time (5us/Div)
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Preliminary
RT9203/A
Short Hiccup
VCC = 5V VOUT = 2.2V
Short Hiccup (Latch Mode)
VCC = 5V VOUT = 2.2V
VOUT VOUT UGATE UGATE
RT9203
RT9203A
Time (2ms/Div)
Time (2ms/Div)
Bootstrap Wave Form
0.803 VCC = 5V, VOUT = 2.2V 0.802 UGATE 0.801
Reference vs. Temperature
Reference (V)
0.800 0.799 0.798 0.797 0.796
LGATE
PHASE
Time (1us/Div)
-50
0
50
100
150
Temperature (C)
IOCSET vs. Temperature
55 50 45 4.3 4.2 4.1
POR (Rising/Falling) vs. Temperature
Rising
IOCSET (uA)1
POR (V)
40 35 30 25 20 -40 -10 20 50 80 110 140
4.0 3.9 3.8 3.7 3.6 -50 0 50 100 150
Falling
Temperature (C)
Temperature (C)
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RT9203/A
315 310
Preliminary
Oscillator Frequency vs. Temperature
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 RT9203/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 RT9203/ A can deliver higher gate driving current while operating with ATX SMPS based on a dual-power supply. The Bootstrap Operation
LGATE VCC 6.0V Regulation BOOT
RT9203/A
R C 1uF 10 12V 5V
+
UGATE
VCC
In a single power supply system, the UGATE driver of RT9203/A is powered by an external bootstrap circuit, as shown in the Figure 3. The boot capacitor, CBOOT , generates a floating reference at the PHASE pin. Typically a 0.1F CBOOT is enough for most of MOSFETs used with the RT9203/A. The voltage drop between BOOT and PHASE is refreshed to a voltage of VCC - diode drop (VD) while the lower MOSFET turning on.
C2 1uF RT9203/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 set to 4.1V with 0.5V hysteresis and the normal level at OCSET pin is set to 1.5V (see over-current protection). The POR function initiates soft-start operation after all supply voltages exceed their POR thresholds. Soft Start
R1 VCC C2 1uF D1 5V 0.1uF
+
BOOT
UGATE
PHASE VCC LGATE
RT9203/A
Figure 3. Single 5V power Supply Operation
A built-in soft-start is used to prevent surge current from power supply input during powering on. The soft-start voltage is controlled by an internal digital counter. It slows down and clamps the ramping of reference voltage at the input of error amplifier and the pulse-width of the output driver. The typical soft-start duration is 2.5ms. Under Voltage and Over Voltage Protection The voltage presents 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 and OV detection are with 30ms delay after triggered. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Figure 5. For RT9203, Only 3 times of trigger are allowed before latching off. But for RT9203A, UVP will be kept in hiccup mode. Hiccup is disabled during soft-start interval.
Dual Power Operation The RT9203/A was designed to supply a regulated 6.0V at VCC pin automatically when BOOT pin is powered by a 12V. In a system with ATX 5V/12V power supply, the RT9203/A is ideal for higher current applications due to the higher gate driving capability, VUGATE = 12V and VLGATE = 6.0V. A RC (10/1F) filter is also recommended at BOOT pin to prevent the ringing induced from fast poweron, as shown in Figure 4.
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RT9203/A
COUNT = 1
Internal
Preliminary
COUNT = 2 COUNT = 3 Q L
4V
SS
2V 0V OVERLOAD
VI
D
C
R
VO
INDUCTOR CURRENT
APPLIED
C.C.M
TS
0A T0 T1 T2 TIME T3 VL
TON
TOFF VI - VO
Figure 5 Inductor Selection The RT9203/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
- VO iL mIL uQ IL = IO
iQ IQ
Because operation frequency is fixed at 300kHz,
TON = 3.33 x VOUT 5V
ID iD
The VOUT ripple is VOUT
RIPPLE = ILRIPPLE x ESR
Figure 6
ESR is the equivalent series resistor of output capacitor Table 1 shows the ripple voltage of VOUT at VIN = 5V Table 1
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
*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
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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 fast load transient requirement. Also high ESR usually induces ripple that may trigger UV or OV protections. So High frequency capacitors with low ESR/ ESL capacitors are recommended here. Linear Regulator Driver The linear controller of RT9203/A was designed to drive an external bipolar NPN transistor or a MOSFET. For a MOSFET, normally DRV need to provide minimum VOUT2+VT+gate-drive voltage to keep VOUT2 as the set voltage. When driving MOSFET operating at a 5V power supply, the gate-drive will be limited at 5V. At this situation, as shown in Figure 7, a MOSFET with low VT threshold (VT = 1V) and set Vout2 below 2.5V are suggested. In VBOOT = 12V operation condition, as Figure 8. shown, VCC is regulated higher than 6V, which providing higher gatedrive capability for driving the MOSFET, VOUT2 can be set as VOUT2 3.3V.
Suggest Low VT MOSFET VOUT2 < 2.5V DRV R3 BOOT FBL R4 VCC VCC = 5V RT9203/A 10 R4<1K 30 20 40
+
RT9203/A
Max. 6V Suggest Low VT MOSFET VOUT2 < 3.3V
+
DRV VBOOT = 12V BOOT 6V FBL R4 VCC RT9203/A R3
R4<1K
Figure 8 PWM Loop Stability The RT9203/A is a voltage mode buck controller designed for 5V step-down applications. The gain of error amplifier is fixed at 35dB for simplifying 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 = 35dB x LC filter pole PO = 1 2 LC 1 2 ESR x C 5 1.75 x 0.8 VOUT
Error Amp pole PA = 300kHz ESR zero ZO =
The RT9203/A Bode plot is as shown in Figure 9. It is stable in most of application conditions.
VOUT = 3.3V COUT = 1500F(33m) L = 2H VOUT = 1.5V VOUT = 2.5V VOUT = 3.3V PO = 2.9kHz ZO = 3.2kHz
Max. 5V
Loop Gain
Figure 7
100
1k
10k
100k
1M
Figure 9
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RT9203/A
Reference Voltage
Preliminary
VIN
Because RT9203/A uses a low 35dB gain error amplifier, as shown in Figure 10. The voltage regulation is dependent on VIN and VOUT settings. The FB reference voltage of 0.8V were trimmed at VIN = 5V and VOUT = 2.5V. In a fixed VIN = 5V application, the FB reference voltage vs. VOUT voltage can be calculated as Figure 11.
L VOUT
+
COUT R1 C1 R2 <1K RT9203/A FB
VOUT = VFB x (1+
R1
R1 R2
)
Figure 12
FB + R1 1K REP 0.8V 56K EA + RAMP 1.75V
PWM
+ -
PWM Layout Considerations MOSFETs switch very fast in efficiency. 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 the layout for component placement 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 lower MOSFET or Schottky diode. Any inductance in the switched current path generates a large voltage spike during the switching interval. Care with component selections, layout of the critical components, and use shorter and wider PCB traces that help in minimizing the magnitude of voltage spikes. There are two sets of critical components in a DC-DC converter using the RT9203/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.
Figure 10
0.82 0.81
FB (V)
0.80 0.79 0.78 10
20
30
40
50 60 Duty (%)
70
80
90
Figure 11 Feedback Divider The reference of RT9203/A is 0.8V. The output voltage can be set using a resistor-divider as shown in Figure 12. Put the R1 and R2 as close as possible to FB pin. R2 value should be less than 1 k to avoid noise coupling issue. 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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Preliminary
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 represent 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 islands 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 IL V OUT Q1 IQ2 Q2 GND
+ + +
RT9203/A
5V
LOAD
GND LGATE VCC RT9203/A UGATE FB
Figure 13
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RT9203/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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