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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