Datasheet RT9202 Datasheet

Page 1

RT9202

Single Synchronous Buck PWM DC-DC Controller

General Description

The RT9202 is a single power supply PWM DC-DC converter controller designed to drive N-Channel MOSFET in a synchronous buck topology. The IC integrates the control, output adjustment, monitoring and protection functions in a small 8-pin package.

The RT9202 uses a low gain 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 300kHz oscillator reduces the component size for saving board space.

The RT9202 features over current protection, over voltage protection, and under voltage lock-out. The output current is monitored by sensing the voltage drop across the MOSFET's R

, which eliminates the need for a

DS(ON)

current sensing resistor.

Ordering Information

RT9202

Package Type S : SOP-8

Operating Temperature Range C : Commercial Standard P : Pb Free with Commercial Standard

Note : RichTek Pb-free products are :

−RoHS compliant and compatible with the current require ments of IPC/JEDEC J-STD-020.

−Suitable for use in SnPb or Pb-free soldering processes.

−100%matte tin (Sn) plating.

Features

l Operate From 5V l 0.8V Internal Reference l Drive Two N-Channel MOSFETs l Voltage Mode PWM Control l Fast Transient Response l Fixed 300kHz Oscillator Frequency l Full 0 to 100% Duty Cycle l Internal Soft Start l Adaptive Non-Overlapping Gate Driver l Over-Current Monitor Uses MOSFET R l Over-Voltage Protection Uses Low-Side MOSFET l RoHS Compliant and 100% Lead (Pb)-Free

DS(ON)

Applications

l Motherboard Power Regulation for Computers l Subsystems Power Supplies l Cable Modems, Set Top Box, and DSL Modems l DSP and Core Communications processor Supplies l Memory Power Supplies l Personal Computer Peripherals l Industrial Power Supplies l 5V-Input DC-DC Regulators l Low Voltage Distributed Power Supplies

Pin Configurations

(TOP VIEW)

BOOT

UGATE

GND

LGATE

2 3 4

PHASE

OCSET

VCC

SOP-8

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RT9202

Typical Application Circuit

SHND

H : shutdown

2N7002

BOOT

UGATE

GND

LGATE

120

R410

0.1uF

OUT

2.5V

255 C6

10nF

D1 MA732

5uH

1000uF

20K

PHASE

OCSET

VCC

1uF

RT9202

Figure 1. RT9202 powered from 5V only

20K

R4 10

1uFC1470uF

12V

SHND

H : shutdown

2N7002

PHASE

OCSET

VCC

1uF

BOOT

UGATE

LGATE

RT9202

GND

120

250 C6

10nF

OUT

2.5V

1uF

5uH

1000uF

1uFC1470uF

Figure 2. RT9202 powered from 12V and 5V

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RT9202

C 1uF

GND

VCC

RT9202

Function Block Diagram

BOOT

OUT

1000uF

BOOT

0.1uF

5uH

G S

IN1

1uF

GND Return

470uF

IN2

Layout Placement

Layout Notes

1. Put CIN1 & CIN2 to be near the MU drain and ML source nodes.

2. Put RT9202 to be near the C

3. Put C

4. Put C

as close as to BOOT pin

BOOT

as close as to VCC pin

VCC

OUT

VCC BOOT

0.5V

Power on

Reset

Soft Start

OVP

UVP +

300kHz

Oscillator

PWM

Control

Logic

GND

Bias

0.8

Reference

0.8V +

Error

1.1V

Error

Amplifier

6.0V

Regulation

40uA

VCC

OCSET

UGATE

PHASE

LGATE

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RT9202

OCSETOCSET

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 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 2)

Connect UGATE pin to the PWM converter's upper MOSFET gate. 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 LGATE to the PWM converter's lower MOSFET gate. This pin provides the gate drive for the lower MOSFET.

OCSET (Pin 7)

Connect a resistor from this pin to the drain of the upper MOSFET. This resistor, an internal 40µA current source, and the upper MOSFET on-resistance set the converter over-current trip point. An over-current trip cycles the softstart function. The voltage at this pin is monitored for power-on reset (POR) purpose and pulling this pin low with an open drain device will shut down the IC.

PEAK

PHASE (Pin 8)

This pin is used to monitor the voltage drop across the upper MOSFET for over-current protection.

DS(ON)

VCC (Pin 5)

This is the main bias supply for the RT9202. This pin also provides the gate bias charge for the lower MOSFET gate. The voltage at this pin is 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.

FB (Pin 6)

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.

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35 38

Absolute Maximum Ratings (Note 1)

RT9202

l Supply Input Voltage, V l BOOT & UGATE to GND--------------------------------------------------------------------------------------------15V l Input, Output or I/O Voltage ----------------------------------------------------------------------------------------GND − 0.3V to 7V l Power Dissipation, P l SOP-8-------------------------------------------------------------------------------------------------------------------0.625W l Package Thermal Resistance (Note 4) l SOP-8, θ l Ambient Temperature Range--------------------------------------------------------------------------------------0°C to +70°C l Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------260°C l Storage Temperature Range-------------------------------------------------------------------------------------- −65°C to +150°C l ESD Susceptibility (Note 2)

-------------------------------------------------------------------------------------------------------------160°C/W

-----------------------------------------------------------------------------------------7V

@ T

= 25°C

HBM (Human Body Mode)-----------------------------------------------------------------------------------------2kV MM (Machine Mode)-------------------------------------------------------------------------------------------------200V

Recommended Operating Conditions (Note 3)

l Junction Temperature Range-------------------------------------------------------------------------------------- −40°C to +125°C

Electrical Characteristics

= 5V, T

= 25° C, Unless otherwise specified.)

Parameter Symbol

Test Conditions Min Typ Max Units

VCC Supply Current / Regulated Voltage

Nominal Supply Current Regulated Voltage from BOOT

ICC VCC V

UGATE, LGATE open -- 3 6 mA

BOOT

= 12V

5 6 7 V

Power-On Reset

Rising VCC Threshold VCC Threshold Hysteresis Rising V

OCSET

Threshold

OCSET

= 4.5V = 4.5V

0.8 1.25 2.0

3.85 4.1 4.35

0.3 0.5 0.7

V V V

Reference

Reference Voltage 0.784 0.8 0.816 V

Oscillator

Free Running Frequency 250 300 350 kHz Ramp Amplitude

∆ V

OSC

-- 1.75

P-P

Error Amplifier

DC gain 32

PWM Controller Gate Driver

Upper Drive Source Upper Drive Sink

Lower Drive Source Lower Drive Sink

UGATE

LGATE

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BOOT= 12V BOOT-V

UGATE

VCC - V V

LGATE

UGATE

= 1V

LGATE

= 1V

= 1V,

-- 7 11

-- 5 7.5

-- 4 6

-- 2 4

To be continued

Ω Ω

Page 6

RT9202

40 45

Parameter Symbol

Protection

FB Over-Voltage Trip FB Rising 1.0 1.1 FB Under-Voltage Trip FB Falling -- 0.5 OCSET Current Source I

OCSET

Test Conditions Min Typ Max Units

= 4.5V 35

OCSET

-- V

0.6

Soft-Start Interval 1 2 4 ms

Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for

stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability.

Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. θJA is measured in the natural convection at TA = 25°C on a low effective thermal conductivity test board of

JEDEC 51-3 thermal measurement standard.

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Typical Operating Characteristic

RT9202

VCC = 5V V

= 2.2V

OUT

UGATE

Dead Time

Time (50ns/Div)

Power On

VCC = 5V

LGATE

Dead Time

VCC = 5V

UGATE

LGATE

Time (50ns/Div)

Power Off

VCC = 5V V

= 2.2V

OUT

Time (2.5ms/Div)

Load Transient

UGATE

OUT

VCC = 5V V

= 2.2V

OUT

= 3000uF

OUT

Time (50ms/Div)

Load Transient

UGATE

VCC = 5V V

= 2.2V

OUT

= 3000uF

OUT

Time (5us/Div)

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RT9202

0.803

0.802

0.801

Bootstrap Wave Form

UGATE

LGATE

PHASE

VCC = 5V, V

OUT

Time (1us/Div)

Reference vs. Temperature

= 2.2V

Short Circuit Hiccup

VCC = 5V, V

OUT

UGATE

Time (5ms/Div)

vs. Temperature

OCSET

OUT

= 2.2V

0.800

0.799

Reference (V)

0.798

0.797

0.796

-50050100150

Temperature

(°C)

POR (Rising/Falling) vs. Temperature

4.3

4.2

4.1

4.0

3.9

POR (V)

3.8

3.7

3.6

-50050100150

Rising

Falling

Temperature

(°C)

(uA)

OCSET

-40-10205080110140

Temperature

(°C)

Oscillator Frequency vs. Temperature

315 310 305 300 295 290 285

Frequency (kHz) A

280 275 270

-50050100150

Temperature

(°C)

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Page 9

Application Information

The RT9202 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 RT9202 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 RT9202 is powered by an external bootstrap circuit, as the Figure 1. The boot capacitor, C floating reference at the PHASE pin. Typically a 0.1µF C

is enough for most of MOSFETs used with the

BOOT

RT9202. The voltage drop between BOOT and PHASE is refreshed to a voltage of VCC − diode drop (VD) while the low side MOSFET turning on.

0.1uF

1uF

VCC

BOOT

UGATE

PHASE

, generates a

BOOT

RT9202

1uF

12VVCC

6.0V

Regulation

1uF

RT9202

BOOT

UGATE

VCC

LGATE

Figure 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.

VCC

LGATE

RT9202

Figure 1. Single 5V power Supply Operation

Dual Power Operation

The RT9202 is 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 RT9202 is ideal for higher current application due to the higher gate driving capability, V

UGATE

= 7V and V

= 6.0V. A RC

LGATE

(10Ω/1µF) filter is also recommended at BOOT pin to prevent the ringing induced from fast power on, as shown in Figure 2.

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.

Over-Current Protection

The over current protection (OCP) function of the RT9202 is triggered when the voltage across the R

DS(ON)

of upper side MOSFET that developed by drain current exceeds over-current tripping level. An external resistor (R

OCSET

programs the over-current tripping level of the PWM converter. As shown on Figure 3 the internal 40µA current sink (I

) develops a voltage across R

OCSET

SET

that is referenced to VIN. The DRIVE signal enables the over-current comparator (OC). When the voltage across the upper MOSFET (V

DS(ON)

) exceeds V

, the over-

SET

current comparator trips to set the over-current latch.

)

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RT9202

DDS(ON)OCSETOCSET

OCSETOCSET

Both V

SET

and V

capacitor across R

are referenced to VIN and a small

OCSET

helps V

tracking the

OCSET

variations of VIN due to MOSFET switching. The overcurrent function will be tripped at a peak inductor current (I

) determined by:

PEAK

The OC trip point varies with MOSFET's R

DS(ON)

temperature variations. The temperature coefficient of I

is 2500ppm that is used to compensate R

OCSET

DS(ON)

temperature variations. To avoid over-current tripping in the normal operating load range, determine the R

OCSET

resistor value from the equation above with:

1.The maximum R

at the highest junction

SD(ON)

temperature

2.The minimum I

3.Determine I

PEAK

from the characteristics

OCSET

for I

PEAK

> I

OUT(MAX)

+ (∆I)/2

where ∆I is the output inductor ripple current.

OVER-CURRENT TRIP: VDS > V

SET

××

PWM

iR>IR

OCSET

40uF

DRIVE

GATE

CONTROL

VCC

OCSET

SET+

UGATE

PHASE

OCSET

= V = V

VIN = +5V

- V

DS+

DS SET

COUNT = 1

COUNT = 2 COUNT = 3

Internal

OVERLOAD

APPLIED

INDUCTOR CURRENT

T1T2

TIME

Figure 4

Shutdown

Pulling low the OCSET pin can shutdown the RT9202 PWM controller as shown in typical application circuit.

Inductor Selection

The RT9202 was designed for VIN = 5V, step-down application mainly. Figure 5 shows the typical topology and waveforms of step-down converter.

The ripple current of inductor can be calculated as follows:

RIPPLE

= (5V - V

OUT

)/L × T

Because operation frequency is fixed at 300kHz, TON = 3.33 × V The V V

ripple is

OUT

OUT RIPPLE

= IL

OUT

RIPPLE

/5V

× ESR ESR is output capacitor equivalent series resistor Table 1 shows the ripple voltage of V

: VIN = 5V

OUT

Under Voltage and Over Voltage Protection

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 30µs triggered delay. When OC or UV trigged, a hiccup re-start sequence will be initialized, as shown in Figure 4. Only 3 times of trigger are allowed to latch off. Hiccup is disabled during softstart interval.

Figure 3

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Table 1

OUT

50.8

2LC

2ESRC

3.3V 2.5V 1.5V

OUT

Inductor 2µH 5µH 2µH 5µH 2µH 5µH 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

*Refer to Sanyo low ESR series (CE, DX, PX.....)

The suggested L and C are as follows:

RT9202

2µH with ≥ 1500µF C

5µH with ≥ 1000µF C

C.C.M

VI - V

OUT

OFF

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, 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

- V

IL = I

UV or OV protections.

PWM Loop Stability

The RT9202 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 1.75V, the loop gain and loop pole/zero are calculated as follows:

DC loop gain GA =

××

35dB

1.75V

LC filter pole PO =

Error Amp pole P ESR zero Z

The RT9202 Bode plot as shown Figure 6 is stable in

Figure 5

DS9202-06 March 2005www.richtek.com

most of application conditions.

= 300kHz

Page 12

RT9202

= 3.3V

OUT

= 1500µF(33mΩ)

OUT

L = 2µH V

= 1.5V

OUT

= 2.5V

OUT

= 3.3V

OUT

Reference Voltage

Because RT9202 use a low 35dB gain error amplifier, shown in Figure 7. The voltage regulation is dependent on V

& V

OUT

were trimmed at VIN = 5V & V fixed VIN = 5V application, the FB reference voltage vs. V

voltage can be calculated as Figure 8.

OUT

PO = 2.9kHz

ZO = 3.2kHz

Loop Gain

1M10k1k100 100k

Figure 6

setting. The FB reference voltage of 0.8V

= 2.5V condition. In a

OUT

Feedback Divider

The reference of RT9202 is 0.8V. The output voltage can be set using a resistor based divider as shown in Figure 9. Put the R1 and R2 as close as possible to FB pin and R2 should 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.

<1K

OUT

RT9202

OUT

Figure 9

PWM Layout Considerations

0.82

0.81

0.80

FB (V)

0.79

0.78

0.5

R1 1K

REP

0.8V

RAMP

1.75V

56K

PWM

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.

MOSFETs switch very fast and efficiently. The speed with

Figure 7

Consider, as an example, the turn-off transition of the upper MOSFET prior to turn-off, the upper MOSFET was

VIN = 5V

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.

OUT

(V)

43.5311.522.5

4.5

Figure 8

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Page 13

There are two sets of critical components in a DC-DC converter using the RT9202. 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.

A multi-layer printed circuit board is recommended. Figure 10 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

RT9202

IQ1

LGATE

UGATE

Figure 10

IQ2

VCCGND

RT9202

OUT

LOAD

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Page 14

RT9202

Outline Dimension

Dimensions In Millimeters

Symbol

Min Max Min Max

A 4.801 5.004 0.189 0.197

Dimensions In Inches

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

RICHTEK TECHNOLOGY CORP.

Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611

8-Lead SOP Plastic Package

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: [email protected]

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