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 “instanton” 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)
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TON |
EN/DEM |
G1 |
BOOT |
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16 |
15 |
14 |
13 |
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VOUT |
1 |
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12 |
UGATE |
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VDD |
2 |
GND |
11 |
PHASE |
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FB |
3 |
10 |
CS |
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PGOOD |
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17 |
VDDP |
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4 |
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9 |
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5 |
6 |
7 |
8 |
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D1 |
D0 |
G0 |
LGATE |
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WQFN-16L 3x3 |
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Features
zUltra-High Efficiency
zResistor Programmable Output Voltage from 0.75V to 3.3V with Integrated Transition Support
zQuick Load Step Response within 100ns
z1% VFB Accuracy over Line and Load
z4.5V to 26V Battery Input Range
zResistor Programmable Frequency
zIntegrated Bootstrap Switch
zResistor Programmable Positive Current Limit by Low Side RDS(ON) Sense (Lossless Limit)
zNegative Current Limiter
zVoltage Transient Overshoot Eliminator*
zOver Voltage Protection
zUnder Voltage Protection
z4 Steps Current Limit During Soft-Start
zPower Good Indicator
zRoHS Compliant and Halogen Free
* Paten Pending
Applications
zNotebook Computers
zSystem Power Supplies
zI/O Supplies
zProgrammable-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
B : G0/G1 Low
Note :
Richtek products are :
`RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`Suitable for use in SnPb or Pb-free soldering processes.
DS8208A/B-04 May 2011 |
www.richtek.com |
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RT8208A/B
Marking Information
RT8208AGQW |
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RT8208BGQW |
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FF= : Product Code |
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FG= : Product Code |
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FF=YM |
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YMDNN : Date Code |
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FG=YM |
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YMDNN : Date Code |
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DNN |
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DNN |
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RT8208AZQW |
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RT8208BZQW |
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FF : Product Code |
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FG : Product Code |
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FF YM |
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YMDNN : Date Code |
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FG YM |
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YMDNN : Date Code |
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DNN |
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DNN |
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Typical Application Circuit
VDDP
PGOOD
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16 |
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9 |
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R1 |
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R2 |
10 |
2 |
100k |
C2 |
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1µF |
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4 |
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10 |
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R6 |
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18k |
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CCM/DEM |
15 |
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17 (Exposed Pad) |
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R3 |
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V |
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250k |
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IN |
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4.5V to 26V |
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RT8208A/B |
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R4 |
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C4 |
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TON |
BOOT |
13 |
0 |
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10µF |
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C3 |
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VDDP |
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R5 |
Q1 |
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UGATE |
12 |
0 |
0.1µF |
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V |
OUT |
= 0.9V |
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BSC119N03S |
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PHASE |
11 |
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L1 |
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VDD |
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1µH |
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R10 |
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8 |
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C1 |
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LGATE |
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Q2 |
R7 |
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C5* |
C6* |
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R8 |
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0 |
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220µF |
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BSC119N03S |
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PGOOD |
G0 |
7 |
G0 |
C7 |
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12k |
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CS |
FB |
3 |
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G1 |
14 |
G1 |
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R11* |
R12* |
R9 |
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5 |
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60k |
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D1 |
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6 |
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EN/DEM |
D0 |
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GND |
VOUT |
1 |
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* : Optional |
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Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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1 |
VOUT |
Output Voltage Pin. Connect to the output of PWM converter. VOUT is an input of |
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the PWM controller. |
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2 |
VDD |
Analog supply voltage input for the internal analog integrated circuit. Bypass to |
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GND with a 1μF ceramic capacitor. |
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3 |
FB |
Feedback Input Pin. Connect FB to a resistor voltage divider from VOUT to GND |
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to adjust output voltage from 0.75V to 3.3V |
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4 |
PGOOD |
Power good signal open-drain output of PWM converter. This pin will be pulled |
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high when the output voltage is within the target range. |
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5 |
D1 |
Drain of the internal MOSFET which is controlled by G1. |
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6 |
D0 |
Drain of the internal MOSFET which is controlled by G0. |
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To be continued |
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www.richtek.com |
DS8208A/B-04 May 2011 |
2
RT8208A/B
Pin No. |
Pin Name |
Pin Function |
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7 |
G0 |
Control Input Pin for the D0 MOSFET. A logic high for RT8208A and low for |
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RT8208B turn on the D0 MOSFET on, pulling D0 to the ground. |
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8 |
LGATE |
Low side N-MOSFET gate driver output for PWM. This pin swings between GND |
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and VDDP. |
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9 |
VDDP |
VDDP is the gate driver supply for external MOSFETs. Bypass to GND with a 1μF |
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ceramic capacitor. |
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10 |
CS |
Over Current Trip Point Set Input. Connect a resistor from this pin to signal ground |
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to set threshold for both over current and negative over current limit. |
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11 |
PHASE |
The UGATE High Side Gate Driver Return. Also serves as anode of over current |
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comparator. |
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12 |
UGATE |
High side N-MOSFET floating gate driver output for the PWM converter. This pin |
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swings between PHASE and BOOT. |
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13 |
BOOT |
Boost Capacitor Connection for PWM Converter. Connect to an external ceramic |
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capacitor to PHASE. |
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14 |
G1 |
Control Input Pin for the D1 MOSFET. A logic high for RT8208A and low for |
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RT8208B turn on the D1 MOSFET on, pulling D1 to the ground. |
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15 |
EN/DEM |
Enable/Diode Emulation Mode Control Input. Connect to VDD for diode–emulation |
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mode, connect to GND for shutdown and floating the pin for CCM mode. |
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16 |
TON |
On Time/Frequency Adjustment Pin. Connect to PHASE through a resistor. TON is |
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an input for the PWM controller. |
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17 (Exposed pad) |
GND |
The exposed pad must be soldered to a large PCB and connected to GND for |
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maximum power dissipation. |
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Function Block Diagram
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G0 |
G1 |
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D0 |
D1 |
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Control |
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TRIG |
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Logic |
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VOUT |
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On-time |
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Compute |
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TON |
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1-SHOT |
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R |
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BOOT |
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SS |
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- |
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- |
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(internal) |
GM |
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+ |
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S |
Q |
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DRV |
UGATE |
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+ |
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Min. TOFF |
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PHASE |
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0.75V VREF |
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Q |
TRIG |
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VDDP |
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+ |
OV |
R Latch |
1-SHOT |
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125% VREF |
S |
Q |
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DRV |
LGATE |
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R Latch |
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70% VREF |
+ |
UV |
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GND |
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S |
Q |
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Diode |
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FB |
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- |
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- |
Emulation |
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90% VREF |
+ |
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10µA |
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Blanking Signal |
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Thermal |
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GM+ |
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CS |
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Shutdown |
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EN |
Counter |
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- |
- |
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SS Timer |
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G0, G1 |
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VDD |
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PGOOD |
EN |
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DS8208A/B-04 |
May 2011 |
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www.richtek.com |
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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 |
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DC ----------------------------------------------------------------------------------------------------------------------------- |
–0.3V to 32V |
< 20ns ----------------------------------------------------------------------------------------------------------------------- |
−8V to 38V |
z UGATE to PHASE |
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DC----------------------------------------------------------------------------------------------------------------------------- |
–0.3V to 6V |
< 20ns ----------------------------------------------------------------------------------------------------------------------- |
−5V to 7.5V |
z LGATE to GND |
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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, PD @ TA = 25°C |
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WQFN−16L 3x3 ------------------------------------------------------------------------------------------------------------ |
1.471W |
z Package Thermal Resistance (Note 2) |
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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) |
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HBM (Human Body Mode) ---------------------------------------------------------------------------------------------- |
2kV |
MM (Machine Mode) ------------------------------------------------------------------------------------------------------ |
200V |
Recommended Operating Conditions |
(Note 4) |
z Input Voltage, VIN ---------------------------------------------------------------------------------------------------------- |
4.5V to 26V |
z Supply Voltage, VDD, VDDP ---------------------------------------------------------------------------------------------- |
4.5V to 5.5V |
z Junction Temperature Range -------------------------------------------------------------------------------------------- |
−40°C to 125°C |
z Ambient Temperature Range -------------------------------------------------------------------------------------------- |
−40°C to 85°C |
Electrical Characteristics
(VIN = 15V, VDD = VDDP = 5V, TA = 25°C, unless otherwise specified)
Parameter |
Symbol |
Test Conditions |
Min |
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Typ |
Max |
Unit |
PWM Controller |
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Quiescent Supply Current |
IQ |
VDD + VDDP, VFB = 0.8V |
-- |
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1250 |
μA |
Shutdown Current |
ISHDN |
VDD + VDDP |
-- |
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1 |
10 |
μA |
EN/DEM = GND |
−10 |
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−1 |
-- |
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FB Reference Voltage |
VREF |
VDD = 4.5V to 5.5V |
0.742 |
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0.750 |
0.758 |
V |
FB Input Bias Current |
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VFB = 0.75V |
−1 |
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0.1 |
1 |
μA |
Output Voltage Range |
VOUT |
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0.75 |
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-- |
3.3 |
V |
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To be continued |
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www.richtek.com |
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DS8208A/B-04 May 2011 |
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4
RT8208A/B
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
D0 Pull-Down Resistance |
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D0 to GND, G0 = 5V |
-- |
10 |
-- |
Ω |
D1 Pull-Down Resistance |
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D1 to GND, G1 = 5V |
-- |
10 |
-- |
Ω |
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On-Time |
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VPHASE = 12V, VOUT = 2.5V, |
336 |
420 |
504 |
ns |
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RTON = 250kΩ |
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Minimum Off-Time |
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250 |
400 |
550 |
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VOUT Shutdown Discharge |
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EN/DEM = GND |
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20 |
-- |
Ω |
Resistance |
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Current Sensing |
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Current Limiter Source Current |
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CS to GND |
9 |
10 |
11 |
μA |
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Current Comparator Offset |
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−10 |
-- |
10 |
mV |
Zero Crossing Threshold |
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PHASE to GND, EN/DEM = 5V |
−10 |
-- |
5 |
mV |
Fault Protection |
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Current Limit (Threshold) |
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GND to PHASE, VCS = 50mV |
40 |
50 |
60 |
mV |
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GND to PHASE, VCS = 200mV |
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200 |
210 |
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Current Limit Setting Range |
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CS to GND |
50 |
-- |
200 |
mV |
Output UV Threshold |
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UVP Detection |
60 |
70 |
80 |
% |
OVP Threshold |
VFB_OVP |
OVP Detection |
120 |
125 |
130 |
% |
OV Fault Delay |
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FB forced above OV threshold |
-- |
20 |
-- |
μs |
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VDD Under Voltage Lockout |
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Rising edge, PWM disabled below |
4.1 |
4.3 |
4.5 |
V |
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this level |
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Threshold |
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Hysteresis |
-- |
80 |
-- |
mV |
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Current Limit Step Duration at |
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Each step |
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128 |
-- |
clks |
Soft-Start |
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UVP Blanking Time |
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From EN signal going high |
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512 |
-- |
clks |
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Thermal Shutdown |
TSHDN |
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155 |
-- |
°C |
Thermal Shutdown Hysteresis |
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-- |
10 |
-- |
°C |
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Driver On-Resistance |
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UGATE Drive Source |
RUGATEsr |
BOOT to PHASE = 5V |
-- |
2 |
5 |
Ω |
UGATE Drive Sink |
RUGATEsk |
BOOT to PHASE = 5V |
-- |
1 |
5 |
Ω |
LGATE Drive Source |
RLGATEsr |
LGATE, High State |
-- |
1 |
5 |
Ω |
LGATE Drive Sink |
RLGATEsk |
LGATE, Low State |
-- |
0.5 |
2.5 |
Ω |
UGATE Gate Driver Source/Sink |
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UGATE to PHASE = 2.5V, |
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1 |
-- |
A |
Current |
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BOOT to PHASE = 5V |
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LGATE Gate Driver Source |
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LGATE forced to 2.5V |
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1 |
-- |
A |
Current |
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LGATE Gate Driver Sink Current |
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LGATE forced to 2.5V |
-- |
3 |
-- |
A |
|
|
|
|
|
|
|
Dead Time |
|
LGATE Rising (Phase = 1.5V) |
-- |
30 |
-- |
ns |
|
|
|
|
|
||
|
UGATE Rising |
-- |
30 |
-- |
||
|
|
|
||||
Internal Boost Charging Switch |
|
VDDP to BOOT, 10mA |
-- |
-- |
80 |
Ω |
On-Resistance |
|
|||||
|
|
|
|
|
|
|
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 |
|
|
|
|
|
V |
|
EN/DEM High |
2.9 |
-- |
-- |
||
|
|
|
|
|
|
|
|
|
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 |
|
Logic Input Current |
|
EN/DEM = 0 |
−5 |
1 |
-- |
μA |
|
|
G0 = G1 = VDD or GND |
−1 |
-- |
5 |
|
PGOOD |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
VFB with respect to Reference, |
87 |
90 |
93 |
|
|
|
PGOOD from Low to High |
|
|||
|
|
|
|
|
|
|
PGOOD Threshold |
|
VFB with respect to Reference, |
-- |
125 |
-- |
% |
|
|
PGOOD from High to Low |
|
|
|
|
|
|
Hysteresis |
-- |
3 |
-- |
|
|
|
|
|
|
|
|
Fault Propagation Delay |
|
Falling edge, FB forced below PGOOD |
-- |
2.5 |
-- |
μs |
|
trip threshold |
|||||
|
|
|
|
|
|
|
Output Low Voltage |
|
ISINK = 1mA |
-- |
-- |
0.4 |
V |
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. θJA is measured in the natural convection at TA = 25°C on a four layers high effective thermal conductivity test board of JEDEC 51-7 thermal measurement standard. The case point of θJC is on the expose pad for 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.
www.richtek.com |
DS8208A/B-04 May 2011 |
6
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