RTQ2816_技术文档

®

RTQ2816

6A, 18V, Synchronous Step-Down Converter

General Description

Features

^Low R_DS(ON)Power MOSFET Switches 26mΩ/19mΩ

^Input Voltage Range : 4.5V to 18V

^Adjustable Switching Frequency : 200kHz to 1.6MHz

^Current-Mode Control

The RTQ2816 is a high efficiency, monolithic synchronous

step-downDC-DC converter that can deliver up to 6Aoutput

current from a 4.5V to 18V input supply. The RTQ2816

current-mode architecture with external compensation

allows the transient response to be optimized over a wide

range of loads and output capacitors. Cycle-by-cycle

current limit provides protection against shorted outputs

and soft-start eliminates input current surge during start-

up. Fault condition protections include output under-voltage

protection, output over-voltage protection, and over-

temperature protection. The low current shutdown mode

provides output disconnection, enabling easy power

management in battery-powered systems.

^Synchronous to External Clock : 200kHz to 1.6MHz

^Accurate Voltage Reference 0.8V 1%, Over −40°C

to 85°C

^Monotonic Start-Up into Pre-biased Outputs

^Adjustable Soft-Start

^Power Good Indicator

^Under-Voltage and Over-Voltage Protection

^Input Under-Voltage Lockout

 RoHS Compliant and Halogen Free

Ordering Information

Applications

RTQ2816

 High Performance Point of Load Regulation

Package Type

QW : WQFN-14AL 3.5x3.5 (W-Type)

 Notebook Computers

 High Density and Distributed Power Systems

Lead Plating System

G : Green (Halogen Free and Pb Free)

Note :

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.

Simplified Application Circuit

RTQ2816

BOOT

VIN

V

IN

C

IN

C

BOOT

L

PVIN

LX

V

OUT

R1

R2

Enable

EN

FB

C

OUT

PGOOD

R

COMP1

R

OSC

COMP

RT/SYNC

SS/TR

C

COMP1

C

COMP2

C

SS

GND

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RTQ2816

Marking Information

Pin Configuration

(TOP VIEW)

1T= : Product Code

YMDNN : Date Code

1T=YM

DNN

1

14

2

3

4

5

6

13

12

11

10

9

GND

PVIN

VIN

BOOT

LX

GND

EN

SS/TR

15

8

7

WQFN-14AL 3.5x3.5

Functional Pin Description

Pin No.

Pin Name

Pin Function

Oscillator resistor and external frequency synchronization input. Connecting a

1

RT/SYNC resistor from this pin to GND sets the switching frequency or connecting an

external clock to this pin changes the switching frequency.

System ground. Provide the ground return path for the control circuitry and

low-side power MOSFET. The exposed pad must be soldered to a large PCB

and connected to GND for minimum power dissipation.

2, 3,

GND

15 (Exposed Pad)

4, 5

6

PVIN

VIN

Power input. Supplies the power switches of the device.

Supply voltage input. Supplies the control circuitry and internal reference of the

device.

Feedback voltage input. This pin is used to set the desired output voltage via an

external resistive divider. The feedback reference voltage is 0.8V typically.

7

8

FB

Compensation node. The current comparator threshold increases with this

control voltage. Connect external compensation elements to this pin to stabilize

the control loop.

COMP

Soft-start and tracking control input. Connect a capacitor from SS to GND to set

the soft-start period. The soft-start period can be used to track and sequence

when the external voltage on this pin overrides the internal reference.

9

SS/TR

Enable control input. Floating this pin or connecting this pin to logic high can

enable the device and connecting this pin to GND can disable the device.

10

11, 12

13

EN

Switch node. LX is the switching node that supplies power to the output and

connect the output LC filter from LX to the output load.

LX

Bootstrap supply for high-side gate driver. Connect a 100nF or greater capacitor

from LX to BOOT to power the high-side switch.

BOOT

Power good indicator output. This pin is an open-drain logic output that is pulled

to ground when the output voltage is lower or higher than its specified threshold

under the conditions of OVP, OTP, dropout, EN shutdown, or during slow start.

14

PGOOD

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RTQ2816

Functional Block Diagram

PGOOD EN

VIN

PVIN

UV

Comparator

Thermal

Detector

I

hys

I

P

UVLO

91% V

REF

PGOOD

Logic

Regulator

Shutdown

109% V

REF

Logic

V

= 1.21V

OV

EN

Comparator

BOOT

LX

Shutdown

Slope

Compensation

High-Side

Current Sense

I

SS

Power Stage

Control

Logic,

Driver, and

Boot UVLO

SS/TR

FB

+

V

REF

+

Current

Comparator

-

Voltage

Reference

Oscillator with

RT/SYNC

Function

Low-Side

Current Sense

GND

COMP

RT/SYNC

Operation

UV Comparator

Error Amplifier

If the feedback voltage (V_FB) is lower than threshold voltage

(91% of V_REF), the UV Comparator's output goes high

and the logic control circuit is allowed to turn on the

MOSFET to pull PGOOD pin to low.

The device uses a transconductance error amplifier. The

error amplifier compares the FB pin voltage with the SS/

TR pin voltage and the internal reference voltage which is

0.8V. The transconductance of the error amplifier is 1300

μA/V during normal operation. The compensation network

should be connected between the COMP pin and ground.

OV Comparator

If the feedback voltage (V_FB) is higher than threshold voltage

(109% of V_REF), the OV Comparator's output goes high

and the logic control circuit is allowed to turn on the

MOSFET to pull PGOOD pin to low.

Oscillator with RT/SYNC Function

The switching frequency is adjustable by an external

resistor connected between the RT/SYNC pin and GND.

The available frequency range is from 200kHz to 1.6MHz.

An internal synchronized circuit has been implemented

to switch from RT mode to SYNC mode. To implement

the synchronization function, connect a square wave clock

signal to the RT/SYNC pin with a duty cycle between

10% to 90%. The switching cycle is synchronized to the

falling edge of the external clock at RT/SYNC pin.

Voltage Reference

The converter produces a precise 1% voltage reference

over-temperature by scaling the output of a temperature

stable bandgap circuit.

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RTQ2816

Absolute Maximum Ratings (Note 1)

 Supply Input Voltage, VIN, PVIN-------------------------------------------------------------------------------- −0.3V to 20V

 SwitchNode Voltage, LX------------------------------------------------------------------------------------------ −1V to 20.3V

LX (t ≤ 10ns) --------------------------------------------------------------------------------------------------------- −5V to (V_IN+ 6.3V)

 BOOT Pin Voltage-------------------------------------------------------------------------------------------------- −0.3V to (V_IN+ 7V)

 Other Pins------------------------------------------------------------------------------------------------------------ −0.3V to 6V

 Power Dissipation, P_D@ T_A= 25°C

WQFN-14AL 3.5x3.5 ---------------------------------------------------------------------------------------------- 2.083W

 Package Thermal Resistance (Note 2)

WQFN-14AL 3.5x3.5, θ_JA----------------------------------------------------------------------------------------- 48°C/W

WQFN-14AL 3.5x3.5, θ_JC---------------------------------------------------------------------------------------- 3.8°C/W

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

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

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

 ESD Susceptibility (Note 3)

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

Recommended Operating Conditions (Note 4)

 Power Input Voltage, PVIN --------------------------------------------------------------------------------------- 1.6V to 18V

 Supply Input Voltage, VIN ---------------------------------------------------------------------------------------- 4.5V to 18V

 Junction Temperature Range------------------------------------------------------------------------------------- −40°C to 125°C

Electrical Characteristics

(V_IN= 4.5V to 18V, V_PVIN= 1.6V to 18V, T_A= −40°C to 85°C, unless otherwise specified)

Parameter

Supply Voltage

Symbol

Test Conditions

Min

Typ

Max

Unit

PVIN Power Input

Operating Voltage

PVIN

V_IN

1.6

4.5

--

18

4.5

--

VIN Supply Input

Operating Voltage

V

Under-Voltage Lockout

Threshold

V_UVLO

V_UVLO

V_INrising

4

Under-Voltage Lockout

Threshold Hysteresis

--

150

mV

VIN Shutdown Current

VIN Quiescent Current

Enable Voltage

V_EN= 0V

--

3

9

A

V_FB= 0.83V, not switching

600

1000

V_IH

V_IL

V_ENrising

V_ENfalling

V_EN= 1.1V

V_EN= 1.3V

--

1.1

--

1.21

1.17

1

1.26

--

EN Threshold Voltage

V

Pull-Up Current

--

A

Hysteresis Current

--

3

--

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RTQ2816

Parameter

Reference Voltage

Symbol

Test Conditions

Min

Typ

Max

Unit

V_REF

0A  I_LOAD 6A

_OSC= 27k

0.792

0.8

0.808

V

Timing Resistor and External Clock

R

1440

400

1600

480

1760

560

Switching Frequency

f_OSC

R_OSC= 110k

R_OSC= 270k

kHz

160

200

240

Include Sync mode and RT

mode set point

Switching Frequency Range

Minimum Sync Pulse Width

200

--

1600

--

20

--

2

ns

V

High-Level

Low-Level

SYNC Threshold Voltage

0.8

--

SYNC Falling Edge to LX

Rising Edge Delay

Measure at 500kHz with R_OSC

resistor in series

--

66

--

ns

Internal MOSFET

High-Side On-Resistance

Low-Side On-Resistance

LX and BOOT

R_{DS(ON)_H}V_BOOT V_LX= 5.5V

--

26

19

40

30

m

R_{DS(ON)_L}V_IN= 12V

Measured at 90% to 90% of V_LX,

I_LX= 2A, 25°C

Minimum On-Time

t_{ON_MIN}

--

135

ns

V

Minimum Off-Time

BOOTLX UVLO

t_{OFF_MIN}

V_BL-UVLO

V_BOOT V_LX 3V

--

0

--

3

--

Soft-Start and Tracking

Internal Charge Current

SS to Feedback Offset

Current Limit

--

2

--

A

V_SS= 0.4V

20

60

mV

High-Side Switch Current

Limit

8

7

--

11

10

--

Low-Side Switch Sourcing

Current Limit

A

Low-Side Switch Sinking

Current Limit

2.3

Error Amplifier

Trans-conductance

2A < I_COMP< 2A,

V_COMP= 1V

gm

--

1300

--

A/V

Error Amplifier DC Gain

V_FB= 0.8V

1000

--

3100

110

16

--

V/V

A

Error Amplifier Sink/Source

Current

V_COMP= 1V, 100mV input

overdrive

COMP to I_switchgm

--

A/V

Power Good

V

_FBrising (Good)

--

94

--

Power Good Rising

Threshold

%V_REF

V_FBrising (Fault)

109

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RTQ2816

Parameter

Symbol

Test Conditions

V_FBfalling (Fault)

Min

--

Typ

91

Max

Unit

--

-

Power Good Falling

Threshold

%V_REF

V_FBfalling (Good)

--

106

Power Good Sink Current

Capability

PGOOD signal fault, I_PGOODsinks

2mA

--

30

0.6

--

0.3

100

1

V

Power Good Leakage

Current

PGOOD signal good, V_PGOOD= 5.5V

nA

Minimum VIN for Indicating

PGOOD

V_PGOOD 0.5V, I_PGOODsinks 100A

V

Minimum SS/TR Voltage for

Indicating PGOOD

2.6

Over-Temperature Protection

Thermal Shutdown

T_SD

160

--

175

10

--

°C

Thermal Shutdown

Hysteresis

T_SD

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_JAis measured under natural convection (still air) at T_A= 25°C with the component mounted on a high effective-

thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. θ_JCis measured at the

exposed pad of the package.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

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RTQ2816

Typical Application Circuit

RTQ2816

13

V

6

IN

BOOT

VIN

4.5V to 18V

C

IN

C

BOOT

0.1µF

L

4, 5

11, 12

PVIN

LX

V

OUT

R1

R2

10

14

Enable

EN

7

8

FB

C

OUT

R

COMP1

PGOOD

COMP

R

OSC

100k

1

9

C

COMP1

C

COMP2

RT/SYNC

SS/TR

C

10nF

SS

2, 3,

15 (Exposed Pad)

GND

Table 1. Suggested Component Values

R

C

COMP2

(pF)

COMP1

(k)

COMP1

(nF)

V

OUT

(V)

R1 (k)

R2 (k)

C

OUT

(F)

L (H)

5.0

3.3

2.5

1.8

1.5

1.2

1.0

126

75

51

30

21

12

6

24

4.3

2.4

8.2

180

22 x 2

4.7

3.7

2.2

1.5

1.8

1.5

1.0

0.82

0.68

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RTQ2816

Typical Operating Characteristics

Efficiency vs. Output Current

100

90

80

70

60

50

40

30

20

10

0

90

V_IN= 9V

V_IN= 12V

V_IN= 17V

80

V_OUT= 5V

V_OUT= 3.3V

V_OUT= 1.2V

70

60

50

40

30

20

10

V_OUT= 3.3V

V_IN= 12V

0

1

2

3

4

5

6

0

1

2

3

4

5

6

Output Current (A)

Output Voltage vs. Output Current

Output Voltage vs. Input Voltage

3.33

3.32

3.31

3.30

3.29

3.28

3.27

3.26

3.37

3.35

3.33

3.31

3.29

3.27

3.25

3.23

I_OUT= 0A

I_OUT= 3A

I_OUT= 6A

V_IN= 12V, V_OUT= 3.3V

V_OUT= 3.3V

16

0

1

2

3

4

5

6

4

6

8

10

12

14

18

Output Current (A)

Input Voltage (V)

Reference Voltage vs. Temperature

Switching Frequency vs. Temperature

0.95

0.90

0.85

0.80

0.75

0.70

0.65

700

650

600

550

500

450

400

350

R_OSC= 100kΩ

-50

-25

0

25

50

75

100

125

-50

-25

0

25

50

75

100

125

Temperature (°C)

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RTQ2816

Shutdown Current vs. Input Voltage

Shutdown Current vs. Temperature

5.1

4.8

4.5

4.2

3.9

3.6

3.3

3.0

18

15

12

9

6

3

V_EN= 0V

0

4

6

8

10

12

14

16

18

-50

-25

0

25

50

75

100

125

Input Voltage (V)

Temperature (°C)

Quiescent Current vs. Input Voltage

Quiescent Current vs. Temperature

1100

1000

900

800

700

600

500

400

1100

1000

900

800

700

600

500

400

V_FB= 0.83V

75 100 125

6

8

10

12

14

16

-25

0

25

50

Input Voltage (V)

Temperature (°C)

Current Limit vs. Input Voltage

Current Limit vs. Temperature

20

17

14

11

8

20

17

14

11

8

5

2

6

8

10

12

14

16

-25

0

25

50

75

100

125

Input Voltage (V)

Temperature (°C)

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RTQ2816

Input Voltage vs. Temperature

EN Voltage vs. Temperature

1.35

1.30

1.25

1.20

1.15

1.10

1.05

4.5

4.4

4.3

4.2

4.1

4.0

3.9

Rising

Falling

Rising

Falling

V_EN= 3.3V

75 100 125

V_IN= 3.3V

100 125

-50

-25

0

25

50

75

-50

-25

0

25

50

Temperature (°C)

Load Transient Response

V_OUT

(1V/Div)

I_OUT

(2A/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 0 to 6A

V_IN= 12V, V_OUT= 3.3V, I_OUT= 1A to 6A

Time (100μs/Div)

Load Transient Response

V_OUT

(500mV/Div)

I_OUT

(1A/Div)

(2A/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 0 to 3A

V_IN= 12V, V_OUT= 3.3V, I_OUT= 3 to 6A

Time (100μs/Div)

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RTQ2816

Voltage Ripple

V_IN

(20mV/Div)

(500mV/Div)

V_OUT

(10mV/Div)

V_LX

(20V/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 0A

V_IN= 12V, V_OUT= 3.3V, I_OUT= 6A

Time (1μs/Div)

Power On from VIN

Power Off from VIN

V_IN

(20V/Div)

V_IN

(20V/Div)

V_PGOOD

(5V/Div)

V_PGOOD

(5V/Div)

V_OUT

(2V/Div)

I_OUT

(5A/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 6A

Time (10ms/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 6A

Time (2.5ms/Div)

Power On from EN

Power Off from EN

V_EN

(5V/Div)

V_PGOOD

(5V/Div)

V_PGOOD

(5V/Div)

V_OUT

(2V/Div)

I_OUT

(5A/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 6A

Time (2.5ms/Div)

V_IN= 12V, V_OUT= 3.3V, I_OUT= 6A

Time (2.5ms/Div)

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RTQ2816

Application Information

This IC is a single phase Buck PWM converter with two

integrated N-MOSFETs. It provides good performance

during load and line transients by implementing a single

feedback loop, current-mode control, and external

compensation. The integrated synchronous power

switches can increase efficiency and it is suitable for lower

duty cycle applications. The switching frequency can be

externally set from 200kHz to 1.6MHz which allows for

high efficiency and optimal size selection of output filter

components. In additional, there is a synchronization

mode control in this device which can be synchronized to

the external clock frequency, and easily switched from

internal switching mode to synchronization mode.

VIN and PVIN Pins

The VINand PVINpins can be used together or separately

for a variety of applications. In this device, the VIN pin is

an input for supplying internal reference and control

circuitry and the PVIN pin is an input for providing main

power to device system and internal high-side power

MOSFET. When the VINand PVINpins are tied together,

both pins can operate from 4.5V to 18V. When the VIN

and PVINpins are used separately, VINpin must be ranged

from 4.5V to 18V, and the PVIN pin can be applied down

to as low as 1.6V to 18V.

The device incorporates an internal under-voltage lockout

(UVLO) circuitry on the VIN pin. If the VIN pin voltage

exceeds the UVLO rising threshold voltage 4V, the

converter resets and prepares the PWM for operation. If

the VIN pin voltage falls below the falling threshold voltage

3.85V during normal operation, the device is disabled.

Such wide internal UVLO hysteresis of 150mV can

efficiently prevent noise caused reset. There is also an

external UVLO circuitry which can be achieved by

configuring a resistive voltage divider on EN pin for both

input VIN and PVIN pins and it is able to provide either

input pins an adjustable UVLO function to ensure a proper

power up behavior. More discussions are located in the

section of Enable Operation.

The device contains a power good protection and an

external soft-start function that is able to monitor the

system output voltage for normal regulation and provides

a programmable power up sequence for avoiding inrush

currents efficiently. Furthermore, the device incorporates

a lot of protections such as OVP, OCP, OTP and etc.

Main Control Loop

The device implements an adjustable fixed frequency with

peak current-mode control which offers an excellent

performance over various line and loading.During normal

operation, the internal high-side power switch is turned

on by the internal oscillator initiating. Current in the

inductor increases until the high-side switch current reaches

the current reference converted by the output voltage V_COMP

of the error amplifier. The error amplifier adjusts its output

voltage by comparing the feedback signal from a resistive

voltage divider on the FB pin with an internal 0.8V

reference. When the load current increases, it causes a

reduction in the feedback voltage relative to the reference.

The error amplifier increases its current reference until

the average inductor current matches the new load current.

When the high-side power MOSFET turns off, the low-

side synchronous power switch (N-MOSFET) turns on

until the beginning of the next clock cycle.

Output Voltage Setting

The resistive voltage divider allows the FB pin to sense

the output voltage as shown in Figure 1.

V

OUT

R1

FB

RTQ2816

GND

R2

Figure 1. Setting the Output Voltage

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RTQ2816

For high efficiency, the divider resistance must adopt larger

values, but too large values may induce noises and voltage

errors by the coupled FB pin input current. It is

recommended to use the values between 10kΩ and

100kΩ. The output voltage is set by an external resistive

voltage divider according to the following Equation (1) :

separated inductor current signal is used to monitor over-

current condition, so the maximum output current stays

relatively constant regardless of duty cycle. More

discussions about over-current protection are described

in a later section.

Enable Operation

R1

R2











V_OUT= V_REF1

(1)



The EN pin is an device enable input. Pulling the EN pin

to logic low that is typically less than the set threshold

voltage 1.17V, the device shuts down and enters to low

quiescent current state about 2μA. The regulator starts

switching again once the EN pin voltage exceeds the

threshold voltage 1.21V. In additional, the EN pin is

implemented with an internal pull-up current source which

allows to enable the device when the EN pin is floating.

For general external timing control, the EN pin can be

externally pulled high by adding a capacitor and a resistor

from the VIN pin as Figure 2.

where V_REFis the feedback reference voltage (0.8V typ.).

Soft-Start

The device contains an external soft-start clamp that

gradually raises the output voltage. The soft-start timing

is programmed by the external capacitor between SS/TR

pin andGND. The device provides an internal 2μAcharge

current for the external capacitor. If a 10nF capacitor is

used to set the soft-start, the period can be 4ms. The

calculations for external charge capacitor C_SSand soft-

start time T_SSare shown in Equation (2) :

V

IN

VIN

C

SS

 V

REF

T

SS

=

(2)

R

EN

I

SS

RTQ2816

EN

where C_SSis the external soft-start capacitor, I_SSis the

soft-start charge current (2μA), V_REFis the feedback

reference voltage (0.8V).

C

EN

GND

Figure 2. Enable Timing Control

Once the input voltage falls below UVLO threshold, the

EN pin is pulled low, or the OTP is triggered, the device

stops switching and the SS/TR pin starts to discharge. It

is held such shutdown condition until the event is cleared

and the SS/TR pin has already discharged to ground

ensuring proper soft-start behavior.

An external MOSFET can be added to implement digital

control from the EN pin to ground, as shown in Figure 3.

In this case, there is no need to connect a pull-up resistor

between the VIN and EN pins since the EN pin is pulled

up by the internal current source. The device can simply

achieve the digital control only through an external

MOSFET on EN pin.

During the pre-biased start-up sequence, the output of

device is not discharged by low-side power switch

because the device is designed to prevent low-side

MOSFET sinking. It is allowed to sink when the SS/TR

pin exceeds 2.1V.

VIN

RTQ2816

V

IN

EN

External

Digital Control

GND

Slope Compensation

Slope compensation provides stability in constant

frequency architectures by preventing sub-harmonic

oscillations at duty cycles greater than 50%. It is

accomplished internally by adding a compensating ramp

to the inductor current signal. Normally, the peak inductor

current is remained constant under the whole duty cycle

range when slope compensation is added. For the device,

Figure 3. Digital Enable Control

The ENpin can also be applied to adjust its under-voltage

lockout (UVLO) threshold with two external resistors

divider from the both input VINand PVINpins used together

or separately, and the application structures can refer to

Figure 4, Figure 5, and Figure 6.

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13

RTQ2816

Separated

Supply

Adjustable Operating Frequency-RT Mode

PVIN

RTQ2816

R

EN1

Selection of the operating frequency is a tradeoff between

efficiency and component size. Higher operating frequency

allows the use of smaller inductor and capacitor values

but it may press the minimum controllable on-time to affect

devices stability. Lower operating frequency improves

efficiency by reducing internal gate charge and switching

losses but requires larger inductance and capacitance to

maintain low output ripple voltage.

EN

EN2

GND

Figure 4. ResistorDivider for PVINUVLO Setting

Separated

VIN

Supply

R

RTQ2816

EN

EN1

EN2

The operating frequency of the device is determined by

an external resistor R_OSC, that is connected between the

RT/SYNC pin and ground. The value of the resistor sets

the ramp current which is used to charge and discharge

an internal timing capacitor within the oscillator. The

practical switching frequency ranges from 200kHz to

1.6MHz. Determine the R_OSCresistor value by examining

the curve in Figure 7.

GND

Figure 5. ResistorDivider for VIN UVLO Setting,

VIN ≥ 4.5V

Combined

PVIN

Supply

VIN

R

EN1

EN2

RTQ2816

EN

1600

GND

1400

1200

1000

800

Figure 6. ResistorDivider for PVINand VINUVLO

Setting

Under above application structures, the adjustable UVLO

function of EN pin allows to achieve a secondary UVLO

on PVIN pin, a higher UVLO on VIN pin or even a common

UVLO on both VINand PVINpins. For example, if the EN

pin is configured as Figure 5 and the output voltage is set

to a higher value 10V. The device may shut down after

soft-start sequence is over, and the reason for the result

is that the V_OUTis still lower than its set target during the

V_INrising period even though V_INhas already risen to its

internal UVLO threshold 4V. To prevent this situation, an

adjustable UVLO threshold from EN pin is useful to avoid

such high output transfer condition. The exact UVLO

thresholds can be calculated by Equation (3). The setting

V_OUTis 10V and V_INis from 0V to 18V. When V_INis higher

than 12V, the device is triggered to enable the converter.

Assume R_EN1= 56kΩ. Then,

600

400

200

0

50

100

150

200

250

300

Ω

R_OSC(k )

Figure 7. Switching Frequency vs. R_OSCResistor

Synchronization-SYNC Mode

The device is allowed to synchronize with an external

square wave clock ranging from 200kHz to 1.6MHz applied

to the RT/SYNC pin. The range of sync duty cycle must

be from 20% to 80%, and the amplitude of sync signal

must be higher than 2V and lower than 0.8V. During the

SYNC mode operation, the switching cycle of LX pin is

synchronized to the falling edge of the external sync

signal.

R_EN1 V

IH

R_EN2

=

(3)

V_{IN_S} V

IH

where V_IHis the typical threshold of enable rising (1.21V)

and V_{IN_S}is the target turn on input voltage (12V in this

example). According to the equation, the suggested

resistor R_EN2is 6.28kΩ.

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DSQ2816-00 August 2019

RTQ2816

5V

Before the external sync signal is provided to the RT/

SYNC pin, the device operates at the original switching

frequency set by resistor R_OSC. When the sync signal is

provided, the SYNC mode overrides the RT mode to force

the device synchronizing to external frequency. This IC

can easily switch between RT mode and SYNC mode,

and the application structure can be configured as Figure

BOOT

RTQ2816

SW

1µF

Figure 9. External Bootstrap Diode

Inductor Selection

8.

External

Sync Signal

RT/SYNC

RTQ2816

GND

For a given input and output voltage, the inductor value

and operating frequency determine the ripple current. The

ripple current ΔI_Lincreases with higher VINand decreases

with higher inductance.

R

OSC

Figure 8. External Sync Signal Control

Power Good Output

V

f L

V_OUT

V

IN



_OUT 

 1

 



I_L=

(4)









 

Having a lower ripple current reduces not only the ESR

losses in the output capacitors but also the output voltage

ripple. Highest efficiency operation is achieved by reducing

ripple current at low frequency, but it requires a large

inductor to attain this goal.

The power good output is an open-drain output and needs

to connect a voltage source below 5.5V with a pull-up

resistor for avoiding the PGOOD floating. When the output

voltage is 9% above or 9% below its set voltage, PGOOD

is pulled low. It is held low until the output voltage returns

within the allowed tolerances 6% once more.During soft-

start, PGOOD is actively held low when V_INis greater

than 1V and is only allowed to be high when soft-start

period is over that means the SS/TR pin exceeds 2.1V

typically and the output voltage reaches 94% of its set

voltage. Besides, the PGOOD pin is also pulled low when

the input UVLO or OVP are triggered, EN pin is pulled

below 1.21V or the OTP is occurred.

For the ripple current selection, the value of ΔI_L= 0.24

(I_MAX) is a reasonable starting point. The largest ripple

current occurs at the highest V_IN. To guarantee that the

ripple current stays below a specified maximum, the

inductor value should be chosen according to the following

equation :



 



V

f  I

V

OUT

V

IN(MAX)

OUT

L =

 1

(5)



 



L(MAX)



 



In this device, 3.7μH is recommended for initial design.

The current rating of the inductor (caused a 40°C

temperature rising from 25°C ambient) must be greater

than the maximum load current and ensure that the peak

current does not saturate the inductor during short-circuit

condition. Referring the Table 1 for the inductor selection

External Bootstrap Diode

Connect a 100nF low ESR ceramic capacitor between

the BOOT and SW pins. This capacitor provides the gate

driver voltage for the high-side MOSFET.

It is recommended to add an external bootstrap diode

between an external 5V and the BOOT pin for efficiency

improvement when input voltage is lower than 5.5V or duty

ratio is higher than 65% .The bootstrap diode can be a

low cost one such as IN4148 or BAT54. The external 5V

can be a 5V fixed input from system or a 5V output of the

RTQ2816. Note that the external boot voltage must be

lower than 5.5V.

reference.

Table 1. Suggested Inductors for Typical

Application Circuit

Component

Supplier

TDK

Series

Dimensions (mm)

VLF10045

SLF12565

NR8040

744325

10 x 9.7 x 4.5

12.5 x 12.5 x 6.5

8 x 8 x 4

TDK

TAIYO YUDEN

WE

10.2 x 10.2 x 4.7

12.8 x 12.8 x 6.2

WE

744355

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15

RTQ2816

Input and Output Capacitors Selection

Choose a capacitor rated at a higher temperature than

required. Several capacitors may also be paralleled to

meet size or height requirements in the design. For the

input capacitor, Two 10μF and one 4.7μF low ESR ceramic

capacitors are recommended for bypassing the PVIN pin

and VIN pin respectively and an additional 0.1μF is

recommended to place as close as possible to the IC

input side for high frequency filtering.All the recommended

input and output capacitors can refer to Table 2 for more

detail.

The input capacitance C_INis needed to filter the trapezoidal

current at the Source of the high-side MOSFET. To prevent

large ripple current, a low ESR input capacitor sized for

the maximum RMS current should be used. The RMS

current is given by Equation (6) :

V

IN

V

OUT

(6)

I

= I

1

RMS

OUT(MAX)

IN

The formula above has a maximum at V_IN= 2V_OUT, where

I_RMS= I_OUT/ 2. This simple worst condition is commonly

used for design because even significant deviations do

not offer much relief.

Table 2. Suggested Capacitors for C_INand C_OUT

Location Component Supplier

Part No.

Capacitance (F)

Case Size

1210

C

MURATA

TDK

GRM32ER71C226M

C3225X5R1C226M

GRM31CR60J476M

C3225X5R0J476M

GRM32ER71C226M

C3225X5R1C226M

22

47

22

IN

1210

IN

C

OUT

C

OUT

C

OUT

C

OUT

MURATA

TDK

1206

1210

MURATA

TDK

1210

The selection of C_OUTis determined by the required ESR

to minimize voltage ripple. Moreover, the amount of bulk

capacitance is also a key for C_OUTselection to ensure

that the control loop is stable. Loop stability can be

checked by viewing the load transient response. The

output ripple ΔV_OUTis determined by Equation (7) :

Level Frequency Shift

While the FB pin drops, switching frequency is proportional

to the feedback voltage, this is a level frequency reduced

function which is implemented in the device. For the same

short-circuit example, when the output voltage drops

during over-current condition, the switching frequency is

reduced in direct proportion to the output voltage, so the

low-side MOSFET is turned off long enough to reduce the

inductor current to prevent a current runaway issue. With

function of level frequency reducing, the switching

frequency can reduce from 100%, 50%, then 25% as the

voltage decreases from 0.8V to 0V on FB pin. The principle

of level frequency reducing is also allowed to cover the

soft-start sequence to increase the switching frequency

as feedback voltage increases from 0V to 0.8V.

1







V_OUT I ESR 

(7)

^L





8fC_OUT

Higher values, lower cost ceramic capacitors are now

becoming available in smaller case sizes. Their high ripple

current, high voltage rating and low ESR make them ideal

for switching regulator applications. However, care must

be taken when these capacitors are used at input and

output. When a ceramic capacitor is used at the input

and the power is supplied by a wall adapter through long

wires, a load step at the output can induce ringing at the

input V_IN. At best, this ringing can couple to the output

and be mistaken as loop instability. At worst, a sudden

inrush of current through the long wires can potentially

cause a voltage spike at V_INlarge enough to damage the

part.

Output Over-Voltage Protection

The device provides an output over-voltage protection

(OVP) once the output voltage exceeds 109% of V_OUT

,

the OVP function turns off the high-side power MOSFET

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DSQ2816-00 August 2019

RTQ2816

to stop current flowing to the output which can only be

released when the output voltage drops below 106% of

V_OUT. There is a 5μs delay also built into the over-voltage

protection circuit to prevent false transition. Using this

OVP feature can easily minimize the output overshoot.

incorporating this additional protection, the device is able

to prevent an excessive sinking current from the load during

the condition of pre-biased output and the SS/TR pin is

asserted high that is 2.1V or above.

Over-Temperature Protection

High-Side MOSFET Over-Current Protection

An over-temperature protection (OTP) is contained in the

device. The protection is triggered to force the device

shutdown for protecting itself when the junction

temperature exceeds 175°C typically. Once the junction

temperature drops below the hysteresis 10°C typically,

the device is re-enable and automatically reinstates the

power up sequence.

The over-current protection (OCP) of high-side MOSFET

is implemented in this device, it adopts monitoring inductor

current during the on-state to control the COMP pin voltage

for turning off the high-side MOSFET. Each cycle the

separated inductor current signal is compared through

sensing the external inductor current to the COMP pin

voltage from an error amplifier output. If the separated

inductor current peak value exceeds the set current limit

threshold, the high-side power switch is turned off.

Thermal Considerations

The junction temperature should never exceed the

absolute maximum junction temperature T_J(MAX), listed

under Absolute Maximum Ratings, to avoid permanent

damage to the device. The maximum allowable power

dissipation depends on the thermal resistance of the IC

package, the PCB layout, the rate of surrounding airflow,

and the difference between the junction and ambient

temperatures. The maximum power dissipation can be

calculated using the following formula :

Low-Side MOSFET Over-Current Protection

The device not only implements the high-side over-current

protection but also provides the over sourcing current

protection and over sinking current protection for low-side

MOSFET. With these three current protections, the IC

can easily control inductor current at both side power

switches and avoid current runaway for short-circuit

condition.

P_D(MAX)= (T_J(MAX)− T_A) / θ_JA

For the sourcing current protection, there is a specific

comparator in internal circuitry to compare the low-side

MOSFET sourcing current to the internal set current limit

at the end of every clock cycle. When the low-side

sourcing current is higher than the set sourcing limit, the

high-side power switch is not turned on and low-side power

switch is kept on until the following clock cycle for releasing

the above sourcing current to the load. It is allowed to

turn on the high-side MOSFET again when the low-side

current is lower than the set sourcing current limit at the

beginning of a new cycle.

where T_J(MAX)is the maximum junction temperature, T_Ais

the ambient temperature, and θ_JAis the junction-to-ambient

thermal resistance.

For continuous operation, the maximum operating junction

temperature indicated under Recommended Operating

Conditions is 125°C. The junction-to-ambient thermal

resistance, θ_JA, is highly package dependent. For a

WQFN-14AL3.5x3.5 package, the thermal resistance, θ_JA,

is 48°C/W on a standard JEDEC 51-7 high effective-

thermal-conductivity four-layer test board. The maximum

power dissipation at T_A= 25°C can be calculated as below :

For the sinking current protection, it is implemented by

detecting the voltage across the low-side power switch. If

the low-side reverse current exceeds the set sinking limit,

both power switches are off immediately, and it is held to

stop switching until the beginning of next cycle. By

P_D(MAX)= (125°C − 25°C) / (48°C/W) = 2.083W for a

WQFN-14AL 3.5x3.5 package.

The maximum power dissipation depends on the operating

ambient temperature for the fixed T_J(MAX)and the thermal

resistance, θ_JA. The derating curves in Figure 10 allows

the designer to see the effect of rising ambient temperature

on the maximum power dissipation.

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RTQ2816

2.5

Layout Considerations

Four-Layer PCB

Follow the PCB layout guidelines for optimal performance

of the device.

2.0

1.5

1.0

0.5

0.0

 Keep the traces of the main current paths as short and

wide as possible.

 Put the input capacitor as close as possible to VIN and

PVIN pins.

 LX node is with high frequency voltage swing and should

be kept at small area. Keep analog components away

from the LX node to prevent stray capacitive noise pickup.

0

25

50

75

100

125

Ambient Temperature (°C)

 Connect feedback network behind the output capacitors.

Keep the loop area small. Place the feedback

components near the device.

Figure 10.Derating Curve of Maximum Power

Dissipation

 Connect all analog grounds to a common node and then

connect the common node to the power ground behind

the output capacitors.

 An example of PCB layout guide is shown in Figure 11

for reference.

Place the input and output capacitors

as close to the IC as possible.

R

OSC

1

14

2

3

4

5

6

13

12

11

10

9

GND

PVIN

VIN

BOOT

C

BOOT

L

C

OUT

LX

C

PVIN

GND

V

EN

SS/TR

OUT

15

8

LX should be connected

7

to inductor by wide and

short trace, and keep

sensitive components

away from this trace.

C

SS

R2

C

VIN

R

COMP

Place the feedback

components as close

to the IC as possible.

R1 C

COMP

Figure 11. PCB Layout Guide

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DSQ2816-00 August 2019

RTQ2816

Outline Dimension

1

2

1

2

DETAILA

Pin #1 ID and Tie Bar Mark Options

Note : The configuration of the Pin #1 identifier is optional,

but must be located within the zone indicated.

Dimensions In Millimeters

Dimensions In Inches

Symbol

Min.

0.700

0.000

0.175

0.200

3.400

2.000

Max.

0.800

0.050

0.250

0.300

3.600

2.100

Min.

0.028

0.000

0.007

0.008

0.134

0.079

Max.

0.031

0.002

0.010

0.012

0.142

0.083

A

A1

A3

b

D

D2

D3

E

0.200

0.008

3.400

2.000

3.600

2.100

0.134

0.079

0.142

0.083

E2

E3

e

0.325

0.500

1.500

0.350

0.013

0.020

0.059

0.014

e1

K

L

0.350

0.450

0.014

0.018

W-Type 14AL QFN 3.5x3.5 Package

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19

RTQ2816

Footprint Information

Footprint Dimension (mm)

P1 Ax Ay Bx By

0.50 1.50 4.30 4.30 2.60 2.60 0.85 0.30 0.75 2.05 2.05 3.50

Number

Package

of Pin

Tolerance

±0.05

P

C

D

Sx Sx1 Sy Sy1

V/W/U/XQFN3.5*3.5-14A

14

Richtek Technology Corporation

14F, No. 8, Tai Yuen 1^stStreet, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

Richtek products are sold by description only. Customers should obtain the latest relevant information and data sheets before placing orders and should verify

that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek

product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use;

nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent

or patent rights of Richtek or its subsidiaries.

www.richtek.com

20

DSQ2816-00 August 2019


型号：	RTQ2816
厂家：	RICHTEK TECHNOLOGY CORPORATION
描述：	暂无描述
文件：	总20页 (文件大小：221K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

RTQ2816 [RICHTEK]

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