Richtek RT8820A Datasheet

RT8820A

Dual-Pha se PWM Controller with PWM-VID Reference

General Description

The RT8820A is a 2/1 phase synchronous Buck PWM

controller which is optimized for high performance graphic

microprocessor and computer applications. The IC

integrates a Constant-On-Time (COT) PWM controller, two

MOSFET drivers with internal bootstrap diodes, as well

as channel current balance and protection functions

including Over-Voltage Protection (OVP), Under-Voltage

Protection (UVP), current limit, and thermal shutdown into

the WQFN-20L 3x3 package.

The RT8820A adopts R

Current limit is accomplished through continuous inductor-

current-sense, while R

accurate channel current balance. Using the method of

current sampling utilizes the best advantages of each

technique.

The RT8820A features external reference input and PWM-

VID dynamic output voltage control, in which the feedback

voltage is regulated and tracks external input reference

voltage. Other features include adjustable switching

frequency, dynamic phase number control, internal soft-

start, power good indicator, and enable functions.

current sensing technique.

DS(ON)

current sensing is used for

DS(ON)

Features



Dual-Phase PWM Controller





 Power State Indicator





 1P-CCM/2P-CCM/1P-DEM/2P-DEM





 Two Embedded MOSFET Drivers and Embedded



Switching Boot Diode



 Support 1.8V PWM-VID Interface



 External Reference Input Control



 PWM-VID Dynamic Voltage Control



 Dynamic Phase Number Control



 Lossless R



 Internal/External Soft-Start



 Adjustable Current Limit Threshold



 Adjustable Switching Frequency



 UVP/OVP Protection



 Shoot Through Protection and Short Pulse Free



Current Sensing for Current Balance

DS(ON)

Technology



 Support an Ultra-Low Output Voltage as Standby



Voltage



 Thermal Shutdown



 Power Good Indicator (EN to PG high = 500



μμ

μs)

μμ

Applications

Ordering Information

RT8820A

Package Type QW : WQFN-20L 3x3 (W-Type)

Lead Plating System G : Green (Halogen Free and Pb Free)

Note :

 CPU/GPU Core Power Supply

 Desktop PC Memory, VTT Power

 Chipset/RAM Power Supply

 Generic DC-DC Power Regulator

Pin Configuration

(TOP VIEW)

Richtek 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.

Marking Information

KP= : Product Code

KP=YM

DNN

YMDNN : Date Code

PHASE1

BOOT1

UGATE1

EN PSI VID VSNS

GND

REFADJ

PHASE2

LGATE1

LGATE2

PVCC

17181920

BOOT2

UGATE2

PGOOD

TON

OCSET/SS

115

RGND

9876

VREF

REFIN

WQFN-20L 3x3

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RT8820A

Functional Pin Description

Pin No. Pin Name Pin Function

1 BOOT1 Bootstrap supply for PWM1. This pin powers the high-side MOSFET driver.

2 UGATE1

3 EN

4 PSI

5 VID

6 REFADJ Reference adjustment output. Refer to PWM-VID Dynamic Voltage Control.

7 REFIN External reference input.

8 VREF

9 TON

10 RGND Negative remote sense input. Connect this pin to the ground of output load.

11 VSNS

12 OCSET/SS

13 PGOOD Power good indicator output. Active high open-drain output.

14 UGATE2

High-side gate driver of PWM1. This pin provides the gate drive for the converter's high-side MOSFET. Connect this pin to the gate of high-side MOSFET.

Enable control input. Active high input. When PVCC POR, the input voltage must not be over PVCC.

Power saving interface. When the voltage is pulled below 0.4V, the device operates into 1 phase DEM. When the voltage is between 0.7V to 0.88V, the device operates into 1 phase forced CCM. When the voltage is between 1.08V to

1.35V, the device operates into 2 phase DEM. W hen the voltage is between 1.6V to 5.5V, the device operates into 2 phase forced CCM.

Programming output voltage control input. Refer to PWM-VID Dynamic Voltage Control.

Reference voltage output. This is a high precision voltage reference (2V) from the VREF pin to RGND pin.

On-time/switching frequency adjustment input. Connecting a 100pF ceramic capacitor between C

Positive remote sense input. Connect this pin to the positive terminal of output load.

Current limit setting. Connect a resistor from OCSET/SS to GND to set the current limit threshold. The external soft start time also can be set through by connecting a capacitor from OCSET/SS pin to GND.

High-side gate driver of PWM2. This pin provides the gate drive for the converter's high-side MOSFET. Connect this pin to the gate of high-side MOSFET.

and ground is optional for noise immunity enhancement.

TON

15 BOOT2 Bootstrap supply for PWM2. This pin powers the high-side MOSFET driver.

Switch node for PWM2. This pin is return node of the high-side driver of PWM 2.

16 PHASE2

17 LGATE2

18 PVCC

19 LGATE1

20 PHASE1

(Exposed Pad)

GND

Connect this pin to the source of high-side MOSFET together with the drain of low-side MOSFET and the inductor.

Low-side gate driver of PWM2. This pin provides the gate drive for the converter's low-side MOSFET. Connect this pin to the gate of low-side MOSFET.

Supply voltage input. Connect this pin to a 5V bias supply. Place a high quality bypass capacitor from this pin to GND.

Low-side gate driver of PWM1. This pin provides the gate drive for the converter's low-side MOSFET. Connect this pin to the gate of low-side MOSFET.

Switch node for PWM1. This pin is return node of the high-side driver of PWM 1. Connect this pin to the Source of high-side MOSFET together with the drain of low-side MOSFET and the inductor.

Ground. The Exposed pad should be soldered to a large PCB and connected to GND for maximum thermal dissipation.

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Functional Block Diagram

VREF

VID

REFADJ

PSI

REFIN

RGND

150% REFIN

or 2V

40% REFIN

Mode Select

Reference

Output Gen.

Power On Reset

& Central Logic

Control & Protection Logic

Boot-Phase Detection 1

RT8820A

PVCC

PGOOD

VSNS

TON

OCSET/SS

Soft-Start

& Slew Rate

Control

Enable

Logic

To Power On Reset

ICS 10µ

To Driver Logic To Power On Reset

VIN

Detection

ICS 40µ

PWM

CMP

To Protection Logic

To SSOK

X(-1/12)

TON

Gen 1

TON

Gen 2

Current

Balance

Current

Limit

Boot-Phase Detection 2

PWM1

PWM2

S/H

Driver

Logic

BOOT1 UGATE1 PHASE1

LGATE1

BOOT2 UGATE2 PHASE2

LGATE2

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RT8820A

Operation

The RT8820A is a dual-phase synchronous Buck PWM

controller with integrated drivers which are optimized for

high performance graphic microprocessor and computer

applications. The IC integrates a COT (Constant-On-Time)

PWM controller with two MOSFET drivers, as well as

output current monitoring and protection functions.

Referring to the function block diagram of TON Genx, the

synchronous UGATE driver is turned on at the beginning

of each cycle. After the internal one-shot timer expires,

the UGATE driver is turned off. The pulse width of this

one-shot is determined by the converter's input voltage

and the output voltage to keep the frequency fairly constant

over the input voltage range and output voltage. Another

one-shot sets a minimum off-time.

The RT8820A also features a PWM-VID dynamic voltage

control circuit driven by the pulse width modulation

method. This circuit reduces the device pin count and

enables a wide dynamic voltage range.

Soft-Start (SS)

For soft-start function, an internal current source charges

an internal capacitor to build the soft-start ramp voltage.

The output voltage will track the internal ramp voltage during

soft-start interval.

PGOOD

The power good output is an open-drain architecture.

When the soft-start is finished, the PGOOD open-drain

output is high impedance.

Current Balance

The RT8820A implements internal current balance

mechanism in the current loop. The RT8820A senses per

phase current and compares it with the average current. If

the sensed current of any particular phase is higher than

average current, the on-time of this phase is adjusted to

be shorter.

Current Limit

The current limit circuit employs a unique “valley” current

sensing algorithm. If the magnitude of the current sense

signal at PHASE is above the current limit threshold, the

PWM is not allowed to initiate a new cycle. Thus, the

current to the load exceeds average output inductor

current, the output voltage falls and eventually crosses

the under-voltage protection threshold, inducing IC

shutdown.

Over-Voltage Protection (OVP) & Under-Voltage Protection (UVP)

The output voltage is continuously monitored for over-

voltage and under-voltage protection. When the output

voltage exceeds its set voltage threshold (If V

OV = 2V, or V

> 1.33V, OV = 1.5 x V

REFIN

≤ 1.33V,

), UGATE

goes low and LGATE is forced high; when it is less than

40% of its set voltage, under voltage protection is triggered

and then both UGATE and LGATE gate drivers are forced

low. The controller is latched until PVCC is re-supplied

and exceeds the POR rising threshold voltage or EN is

reset.

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RT8820A

Absolute Maximum Ratings (Note 1)

 TON to GND ------------------------------------------------------------------------------------------------------------------ −0.3V to 30V

 RGND to GND --------------------------------------------------------------------------------------------------------------- −0.7V to 0.7V

 BOOTx to PHASEx

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

<100ns ------------------------------------------------------------------------------------------------------------------------ −5V to 7.5V

 BOOTx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 36V

<100ns ------------------------------------------------------------------------------------------------------------------------ −5V to 42V

 PHASEx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −5V to 30V

<100ns ------------------------------------------------------------------------------------------------------------------------ −10V to 42V

 UGATEx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −5V to 36V

<100ns ------------------------------------------------------------------------------------------------------------------------ −10V to 42V

 UGATEx to PHASEx

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

<100ns ------------------------------------------------------------------------------------------------------------------------ −5V to 7.5V

 LGATEx to GND

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

<100ns ------------------------------------------------------------------------------------------------------------------------ −5V to 7.5V

 Other Pins-------------------------------------------------------------------------------------------------------------------- −0.3V to 6.5V

 Power Dissipation, P

WQFN-20L 3x3 ------------------------------------------------------------------------------------------------------------- 2.67W

 Package Thermal Resistance (Note 2)

WQFN-20L 3x3, θJA-------------------------------------------------------------------------------------------------------- 30°C/W

WQFN-20L 3x3, θJC------------------------------------------------------------------------------------------------------- 7.5°C/W

 Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------- 260°C

 Junction Temperature ------------------------------------------------------------------------------------------------------ 150°C

 Storage Temperature Range --------------------------------------------------------------------------------------------- −65°C to 150°C

 ESD Susceptibility (Note 3)

HBM (Human Body Model)----------------------------------------------------------------------------------------------- 2kV

@ T

= 25°C

Recommended Operating Conditions (Note 4)

 Input Voltage, VIN ---------------------------------------------------------------------------------------------------------- 2.5V to 26V

 Supply Voltage, PVCC ---------------------------------------------------------------------------------------------------- 4.5V to 5.5V

 Junction Temperature Range --------------------------------------------------------------------------------------------- −10°C to 105°C

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RT8820A

Electrical Characteristics

= 5V, typical values are referenced to TA = TJ = 25°C, Min and Max values are referenced to TA = TJ from −10°C to

PVCC

105°C, unless other noted)

Parameter Symbol Test Conditions Min Typ Max Unit

PWM Controller

PVCC Supply Voltage V

PVCC Supply Current I

PVCC Shutdown Current I

PVCC POR Threshold 3.8 4.1 4.4 V

POR Hysteresis -- 0.3 -- V

Switching Frequency fSW R

Minimum On-Time t

Minimum Off-Time t

EN Inpu t Voltage

Logic-High V

EN Input Voltage

Logic-Low V

Mode Decision

2 Phase CCM V

2 Phase DEM V

1 Phase CCM V

1 Phase DEM V

PWM-VID Input Vol t age for 1. 8V G PIO Set t ing

4.5 -- 5.5 V

PVCC

= 3.3V, 1phase DEM mode,

SUPPLY

not switching, VREF external R =

-- 0.4 -- mA

40k

SHDN

ON(MIN)

OFF(MIN)

-- 70 -- ns

1.2 -- 5.5

EN_H

-- -- 0.55

EN_L

1.6 1.8 5.5 V

PSI

1.08 1.2 1.35 V

PSI

0.7 0.8 0.88 V

PSI

-- 0 0.4 V

PSI

= 0V -- -- 10 A

= 500k (Note 5) 270 300 330 kHz

TON

-- 300 -- ns

Logic H V

Logic L V

PWM-VID_H

PWM-VID_L

1.2 -- -- V

-- -- 0.6 V

Protect io n Function

Zero Current Crossing Threshold

Current Limit Setting Current I

Current Limit Setting Current Temperature Coefficient

Current Limit Threshold R

Absolute Over-Voltage Protection Threshold Relative Over-Voltage Protection Threshold

8 -- 8 mV

OCSET

OCSET_TC

OVP, Absolute

OVP, Relative

-- 4700 -- ppm/C

= TJ = 25C 9 10 11 A

= 120k -- 100 -- mV

OCSET

 1.33V 1.9 2 2.1 V

REFIN

> 1.33V 145 150 155 %

REFIN

OV Fault Delay FB forced above OV threshold -- 5 -- s

Relative Under-Voltage Protection Threshold

UVP 35 40 45 %

UVP

UV Fault Delay FB forced above UV threshold -- 3 -- s

Thermal Shutdown Threshold

-- 150 -- C

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RT8820A

Parameter Symbol Test Conditions Min Typ Max Unit

VOUT Soft-Start (PGOOD Blanking Time)

From VEN = high to VOUT regulation point, V

REFIN

= 1V

-- 0.5 -- ms

Error Amplifier

VSNS Error Comparator Threshold (Valley)

= 1V 11 6 1 mV

REFIN

Reference

Reference Voltage V

VREF

Sourcing current = 1mA, VID no switching

1.98 2 2.02 V

Driver On-Resistance

UGATE Driver Source R

UGATE Driver Sink R

LGATE Driver Source R

LGATE Driver Sink R

UGATEsr

UGATEsk

LGATEsr

LGATEsk

BOOTx  PHASEx forced to 5V -- 2 4 

BOOTx  PHASEx forced to 5V -- 1 2 

LGATEx, high state -- 1.5 3 

LGATEx, low state -- 0.7 1.5 

From LGATE falling to UGATE rising -- 30 --

Dead-Time

From UGATE falling to LGATE rising -- 20 --

Internal Boost Diode Resistance

Note 1. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.

These are stress ratings only, and 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 may affect device reliability.

Note 2. θ

Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Not production tested. Test condition is V

is measured under natural convection (still air) at T

thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. θ

exposed pad of the package.

BOOT

PVCC to BOOTx, I

= 25°C with the component mounted on a high effective-

= 8V, V

OUT

= 1V, I

= 10mA -- 80 -- 

BOOT

is measured at the

= 20A using application circuit.

OUT

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Richtek RT8820A Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual