Richtek RT8208AGQW, RT8208AZQW, RT8208BGQW, RT8208BZQW Schematic [ru]

RT8208A/B

Programmable Output Voltage Single Synchronous
Buck Controller

General Description

The RT8208A/B is a constant-on-time PWM controller

which provides four resistor programmable DC output

voltages by controlling the G0 and G1 digital input. The

output voltage is programmable from 0.75V to 3.3V. The

RT8208A/B offers the lowest total solution cost in systems

where need output voltage slewing. The RT8208A/B

provides an automatic masking power good output during

output voltage transition.

The constant-on-time PWM control scheme handles wide

input/output ratios with ease and provides 100ns “instant-
on” response to load transient while maintaining a

relatively constant frequency. It provides the high efficiency,

excellent transient response, and DC output accuracy

needed for stepping down high voltage batteries to

generate low voltage CPU core, graphics, I/O and chipset

RAM supplies in notebook computers.

The RT8208A/B achieves high efficiency at a reduced cost

by eliminating the current sense resistor in traditional

current mode PWMs. Efficiency is further enhanced by

its ability to drive very large synchronous rectifier

MOSFETs. The buck conversion allows this device to

directly step down from high voltage batteries for the highest

possible efficiency. Additional features include soft-start,

under voltage protection, programmable over current

protection and non-overlapping gate drive. The RT8208A/

B is available in a WQFN-16L 3x3 package.

Pin Configurations

(TOP VIEW)

TON

EN/DEM

BOOT

G1

13141516

VOUT

VDD

FB

PGOOD

1

2

GND

3

4

D1G0D0

WQFN-16L 3x3

12

UGATE

11

PHASE

10

CS

17

9

VDDP

8765

LGATE

Features

zz

z Ultra-High Efficiency

zz

zz

z Resistor Progra mma ble Output Voltage from 0.75V

zz

to 3.3V with Integrated Transition Support

zz

z Quick Load Step Response within 100ns

zz

zz

z 1% V

zz

zz

z 4.5V to 26V Battery Input Range

zz

zz

z Resistor Programmable Frequency

zz

zz

z Integrated Bootstrap Switch

zz

zz

z Resistor Programmable Positive Current Limit by

zz

Low Side R

zz

z Negative Current Limiter

zz

zz

z Voltage Transient Overshoot Eliminator*

zz

zz

z Over Voltage Protection

zz

zz

z Under Voltage Protection

zz

zz

z 4 Steps Current Limit During Soft-Start

zz

zz

z Power Good Indicator

zz

zz

z RoHS Compliant and Halogen Free

zz

* Paten Pending

Accuracy over Line and Load

FB

Sense (Lossless Limit)

DS(ON)

Applications

z Notebook Computers

z System Power Supplies

z I/O Supplies

z Programmable-Output Power Supplies

Ordering Information

RT8208

Package Type
QW : WQFN-16L 3x3 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)

Turn-on D0/D1 MOSFET
A : G0/G1 High

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.

B : G0/G1 Low

DS8208A/B-04 May 2011 www.richtek.com

1

RT8208A/B

Marking Information

RT8208AGQW

FF= : Product Code

FF=YM

DNN

YMDNN : Date Code

RT8208BGQW

FG=YM

DNN

FG= : Product Code

YMDNN : Date Code

RT8208AZQW

FF : Product Code

FF YM

YMDNN : Date Code

DNN

Typical Application Circuit

R

2

RT8208A/B

1

6

T

O

N

9

V

D

D

2

4

0

5

d

)

P

D

V

D

O

P

G

O

C

S

EN/DEM

D

N

G

D

D

P

D

V

1

R

1

0

2

R

1

0

0

k

2

C

1

µ

F

D

O

G

O

P

D

/

M

C

C

1

E

7

(

p

x

1

6

R

1

8

k

1

M

E

o

e

s

d

P

a

RT8208BZQW

FG : Product Code

FG YM

YMDNN : Date Code

DNN

3
0

5

k

4

R

0

1

B

G

U

P

H

L

G

V

3

O

O

T

C

5

R

0

1

2

A

T

E

1

1

A

S

E

R

1

8

A

T

E

0

7

G

F

B

G

D

D

O

U

T

G

0

3

1

4

G

1

5

1

6

0

1

3

0

1

.

0

B

S

C

1

0

1

V

N

I

4

5

.

o

t

V

2

6

V

4

C

1

0

µ

F

1

µ

F

1

9

Q

B

S

C

1

1

9

N

0

3

S

L

1

1

µ

H

R

Q

N

0

3

S

7

2

C

7

R

1

1

*

R

8

1

2

k

R

R

9

1

2

*

6

0

k

V

=

0

9

.

V

T

U

O

C

C

5

*

C

6

*

1

2

2

0

µ

F

*

O

p

:

a

o

l

i

n

t

Functional Pin Description

Pin No. Pin Name Pin Function

1 VOUT

2 VDD

3 FB

4 PGOOD

5 D1 Drain of the internal MOSFET which is controlled by G1.

6 D0 Drain of the internal MOSFET which is controlled by G0.

2

Output Voltage Pin. Connect to the output of PWM converter. VOUT is an input of
the PWM controller.

Analog supply voltage input for the internal analog integrated circuit. Bypass to
GND with a 1μF ceramic capacitor.
Feedback Input Pin. Connect FB to a resistor voltage divider from VOUT to GND
to adjust output voltage from 0.75V to 3.3V
Power good signal open-drain output of PWM converter. This pin will be pulled
high when the output voltage is within the target range.

To be continued

DS8208A/B-04 May 2011www.richtek.com

Pin No. Pin Name Pin Function

7 G0

8 LGATE

9 VDDP

10 CS

11 PHASE

12 UGATE

13 BOOT

14 G1

15 EN/DEM

16 TON

17 (Exposed pad) GND

Control Input Pin for the D0 MOSFET. A logic high for RT8208A and low for
RT8208B turn on the D0 MOSFET on, pulling D0 to the ground.

Low side N-MOSFET gate driver output for PWM. This pin swings between GND
and VDDP.
VDDP is the gate driver supply for external MOSFETs. Bypass to GND with a 1μF
ceramic capacitor.
Over Current Trip Point Set Input. Connect a resistor from this pin to signal ground
to set threshold for both over c urrent and negative over current limit.
The UGATE High Side Gate Driver Return. Also serves as anode of over current
comparator.
High side N-MOSFET floating gate driver output for the PWM converter. This pin
swings between PHASE and BOOT.
Boost Capacitor Connec tion for PWM Converter. Connect to an external ceramic

capacitor to PHASE.
Control Input Pin for the D1 MOSFET. A logic high for RT8208A and low for
RT8208B turn on the D1 MOSFET on, pulling D1 to the ground.
Enable/Diode Emulation Mode Control Input. Connect to VDD for diode–emulation
mode, connect to GND for shutdown and floating the pin for CCM mode.
On Time/Frequency Adjustment Pin. Connect to PHASE through a resistor. TON is
an input for the PWM controller.
The exposed pad must be soldered to a large PCB and connected to GND for
maximum power dissipation.

Function Block Diagram

RT8208A/B

VOUT

TON

FB

SS

(internal)

125% V

70% V

Blanking Signal

Counter

EN

G0, G1

-

GM

+

0.75V V

REF

REF

TRIG

On-time

Compute

1-SHOT

REF

+

-

+

-

90% V

SS Timer

OV

UV

REF

­+

R

Latch

SQ

R

Latch

SQ

­+

Thermal

Shutdown

G0 G1 D0 D1

Control

Logic

R

QS

Min. T

OFF

QTRIG

1-SHOT

Diode

Emulation

BOOT

DRV

DRV

10µA

+

+

-

GM

-

UGATE

PHASE

VDDP

LGATE

GND

CS

VDD

PGOOD

EN

DS8208A/B-04 May 2011 www.richtek.com

3

RT8208A/B

Absolute Maximum Ratings (Note 1)

z BOOT to GND -------------------------------------------------------------------------------------------------------------- −0.3V to 38V

z BOOT to PHASE ---------------------------------------------------------------------------------------------------------- −0.3V to 6V

z PHASE to GND

DC----------------------------------------------------------------------------------------------------------------------------- –0.3V to 32V

< 20ns ----------------------------------------------------------------------------------------------------------------------- −8V to 38V

z UGATE to PHASE

DC----------------------------------------------------------------------------------------------------------------------------- –0.3V to 6V

< 20ns ----------------------------------------------------------------------------------------------------------------------- −5V to 7.5V

z LGATE to GND

DC----------------------------------------------------------------------------------------------------------------------------- –0.3V to 6

< 20ns ----------------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V

z VDD, VDDP, VOUT, EN/DEM, FB, PGOOD, TON to GND------------------------------------------------------- −0.3V to 6V

z CS to GND ------------------------------------------------------------------------------------------------------------------ −0.3V to 6V

z Power Dissipation, P

WQFN−16L 3x3 ------------------------------------------------------------------------------------------------------------ 1.471W

z Package Thermal Resistance (Note 2)

WQFN−16L 3x3, θJA------------------------------------------------------------------------------------------------------ 68°C/W

WQFN−16L 3x3, θJC------------------------------------------------------------------------------------------------------ 7.5°C/W

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

z Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C

z ESD Susceptibility (Note 3)

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

MM (Machine Mode) ------------------------------------------------------------------------------------------------------ 200V

@ T

D

= 25°C

A

Recommended Operating Conditions (Note 4)

z Input Voltage, V

z Supply Voltage, V

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

z Ambient Temperature Range--------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------- 4.5V to 26V

IN

, V

DD

---------------------------------------------------------------------------------------------- 4.5V to 5.5V

DDP

−40°C to 85°C

Electrical Characteristics

(V

= 15V, V

IN

PWM Con tro ll e r

Quiescent Supply Current IQ VDD + VDDP, VFB = 0.8V -- -- 1250 μA

Shutdown Current I

FB Reference Voltage V

FB Input Bias Current VFB = 0.75V −1 0.1 1 μA

Output Voltage Range V

4

= V

DD

= 5V, TA = 25°C, unless otherwise specified)

DDP

Parameter Symbol Test Conditions Min Typ Max Unit

SHDN

VDD = 4.5V to 5.5V 0.742 0.750 0.758 V

REF

0.75 -- 3.3 V

OUT

EN/DEM = GND −10 −1 --

VDD + V

-- 1 10

DDP

μA

To be continued

DS8208A/B-04 May 2011www.richtek.com

RT8208A/B

Parameter Symbol Test Conditions Min Typ Max Unit

D0 Pull-Down Resistance D0 to GND, G0 = 5V -- 10 -- Ω

D1 Pull-Down Resistance D1 to GND, G1 = 5V -- 10 --

PHASE

= 250kΩ

TON

= 12V, V

On-Time

V
R

= 2.5V,

OUT

336 420 504 ns

Minimum Off-Time 250 400 550 ns

VOUT Shutdown Discharge
Resistance

EN/D EM = GND -- 20 -- Ω

Curren t Sens ing

Current Limiter Source Current CS to GND 9 10 11 μA
Current Comparator Offset −10 -- 10 mV
Zero Crossing Threshold PHASE to GND, EN/DEM = 5V −10 -- 5 mV

Fault Protection

Ω



Current Limit (Threshold)

GND to PHASE, V

= 200mV 190 200 210

CS

mV

Current Limit Setting Range CS to GND 50 -- 200 mV

Output UV Threshold UVP Detection 60 70 80 %

GND to PHASE, VCS = 50mV 40 50 60

OVP Threshold V

FB_OVP

OVP Detection 120 125 130 %

OV Fault Delay FB forced above OV threshold -- 20 -- μs

VDD Under Voltage Lockout
Threshold

Current Limit Step Duration at
Soft-Start

Rising edge, PWM disabled below
this level

Hysteresis -- 80 -- mV

Each step -- 128 -- clks

4.1 4.3 4.5 V

UVP Blanking Time From EN signal going high -- 512 -- clks

Thermal Shutdown T

-- 155 -- °C

SH DN

Thermal Shutdown Hysteresis -- 10 -- °C

Dri ver On-Resis ta nce

UGATE Drive Source R

UGATE Drive Sink R

LGATE Drive Source R

LGATE Drive Sink R

UGATE Gate Driver Source/Sink
Current
LGATE Gate Driver Source
Current

UGATEsr

UGATEsk

LGATEsr

LGATEsk

LGATE forced to 2.5V -- 1 -- A

BOOT to PHASE = 5V -- 2 5 Ω

BOOT to PHASE = 5V -- 1 5

Ω

LGATE, High State -- 1 5 Ω

LGATE, Low State -- 0.5 2.5

UGATE to PHASE = 2.5V,
BOOT to PHASE = 5V

-- 1 -- A

Ω

LGATE Gate Driver Sink Current LGATE forced to 2.5V -- 3 -- A

Dead Time

LGATE Rising (Phase = 1.5V) -- 30 --

ns

UGATE Rising -- 30 --

Internal Boost Charging Switch
On-Resistance

VDDP to BOOT, 10mA -- -- 80 Ω



To be continued

DS8208A/B-04 May 2011 www.richtek.com

5

RT8208A/B

Parameter Symbol Test Conditions Min Typ Max Unit

Logic I/O

EN/DEM Low -- -- 0.8

EN/DEM Logic Input Voltage

EN/DEM H igh 2.9 -- --

V

EN/DEM Floating -- 2 --

G0 Logic Input Voltage

G0 Low -- -- 0.8

V

G0 High 2 -- --

G1 Logic Input Voltage

G1 Low -- -- 0.8

V

G1 High 2 -- --

EN/DEM = VDD -- 1 5
EN/DEM = 0 −5 1 -- Logic Input Current

μA

G0 = G1 = VDD or GND −1 -- 5

PGOOD

with respec t to Referenc e,

V

FB

PGOOD from Low to High

with respec t to Referenc e,

V

FB

PGOOD from High to Low

87 90 93

-- 125 --

%

PGOOD T hreshold

Hysteresis -- 3 --

Fault Propagation Delay

Output Low Voltage I

Falling edge, FB forced be low PGOOD
trip thr eshold

= 1mA -- -- 0.4 V

SINK

-- 2.5 -- μs

Leakage Current High state, forced to 5V -- -- 1 μA



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. θ

Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.

is measured in the natural convection at TA = 25°C on a four layers high effective thermal conductivity test board of

JA

JEDEC 51-7 thermal measurement standard. The case point of θ

is on the expose pad for the package.

JC

DS8208A/B-04 May 2011www.richtek.com

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