RT8561C
High Voltage 8-CH LED Driver
General Description
The RT8561C is a 40V 8-CH LED driver capable of delivering 30mA to each channel with 10 LEDs (3.6V per diode), for a total of 80 LEDs with one driver. The RT8561C is a current mode boost converter that operates at 1MHz, with a wide VIN range from 4.5V to 24V and an on chip current switch rated at 2.5A.
The PWM output voltage loop regulates the LED pins to 0.6V with an auto adjustment circuit allowing voltage mismatches between LED strings. The RT8561C automati cally detects and disconnects any unconnected and/or broken strings during operation from the PWM loop to prevent VOUT from over voltage.
The 1.5% matched LED currents on all channels can be simply programmed with a resistor or a current sink. A very high contrast ratio true digital PWM dimming can be achieved by driving the PWM pin with a PWM signal.
Other protection features include programmable output over voltage protection, LED current limit, PWM switch current limit and thermal shutdown.
The RT8561C is available in a WQFN-24L 4x4 package.
Ordering Information
RT8561C 
Package Type
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Marking Information
E4= : Product Code
E4=YM YMDNN : Date Code
DNN
Features
zHigh Voltage : VIN up to 24V, VOUT up to 40V
zProgrammable Channel Current from 10mA to 30mA and Matched to 1.5%
zCurrent Mode PWM 1MHz Boost Converter
zEasy and High Accuracy Digital Dimming by PWM Signal
zProgrammable Soft-Start
zAutomatic Detection of Unconnected and/or Broken Channel
zProgrammable Over Voltage Protection
zDisconnects LED in Shutdown
zNo Power Sequence Concern
zVIN Under Voltage Lockout
zOver Temperature Protection
zCurrent Limiting Protection
zSmall 24-Lead WQFN Package
zRoHS Compliant and Halogen Free
Applications
zUMPC and Notebook Computer Backlight
zGPS, Portable DVD Backlight
zDesk Lights and Room Lighting
Pin Configurations
(TOP VIEW)
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GND |
GND |
GND |
GND |
LX |
LX |
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24 |
23 |
22 |
21 |
20 |
19 |
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LED1 |
1 |
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18 |
VCC |
LED2 |
2 |
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17 |
CREG |
LED3 |
3 |
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GND |
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16 |
LED8 |
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LED4 |
4 |
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15 |
LED7 |
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LED5 |
5 |
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14 |
LED6 |
OVP |
6 |
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25 |
13 |
EN |
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7 |
8 |
9 |
10 |
11 |
12 |
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VC |
NC |
SS |
RISET |
ACTL |
NC |
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WQFN-24L 4x4 |
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DS8561C-00 April 2011 |
www.richtek.com |
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RT8561C |
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Typical Application Circuit |
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VOUT |
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L1 |
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D1 |
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40V MAX |
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VIN |
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10µH |
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4.5V to 24V |
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C1 |
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C5 |
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R4 |
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10µF |
RT8561C |
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10µF |
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10 |
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18 |
VCC |
LX |
19, 20 |
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... : |
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8 x 10 LED String |
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C6 |
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R7 |
C7 |
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1µF |
R5 |
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1 |
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5V |
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1k |
13 EN |
LED1 |
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R6 1k |
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11 ACTL |
LED2 |
2 |
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PWM Signal |
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... |
... |
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7 VC |
LED7 |
15 |
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LED8 |
16 |
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R2 |
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R1 |
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17 |
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6 |
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C8 |
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CREG |
OVP |
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VOUT |
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1.8k |
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C2 |
C3 |
C4 |
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9 SS |
RISET |
10 |
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R3 |
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4.7µF |
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RISET |
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3.9nF |
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0.1µF |
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4.75k |
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21, 22, 23, 24, |
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ILED (mA) = |
20 x 4.75 |
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25 (Exposed Pad) |
GND |
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RISET (kΩ) |
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Note :
Due to the limitation of maximum duty, 5V input can support typically to VOUT = 33V.
Figure 1. 1MHz, 20mA Full Scale Current PWM Dimming Control
Function Block Diagram
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LX |
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VCC |
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- |
OSC |
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S |
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LED1 |
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4.2V |
+ |
+ |
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R |
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OVP |
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+ |
- |
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R |
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1.2V |
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- |
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EN |
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- |
+ - |
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LED2 |
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1.6V |
+ |
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+ |
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Shutdown |
. |
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5V |
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- |
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CREG |
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. |
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LDO |
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VOUT |
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. |
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VC |
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Regulation |
+ |
LED7 |
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Unit |
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- |
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5µA |
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5V |
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SS |
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+ |
LED8 |
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ACTL |
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+ |
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- |
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GND |
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- |
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RISET |
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www.richtek.com |
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DS8561C-00 |
April |
2011 |
2 |
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RT8561C |
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Functional Pin Description |
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Pin No. |
Pin Name |
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Pin Function |
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LED1, LED2, |
Channel 1 to Channel 5 LED current sink. Leave the pin unconnected if not |
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1, 2, 3, 4, 5 |
LED3, LED4, |
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LED5 |
used. |
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6 |
OVP |
Over Voltage Protection. PWM boost converter turns off when VOVP goes |
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higher than 1.2V. |
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7 |
VC |
PWM boost converter loop compensation node. |
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8 |
NC |
No Internal Connection. |
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9 |
SS |
Soft Start Pin, a capacitor of at least 10nF is required for soft start. |
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10 |
RISET |
A resistor or a current from DAC on this pin programs the full LED current. |
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11 |
ACTL |
Analog/Digital dimming control. When using analog dimming, |
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ILED (mA) = |
20 x 4.75 |
for VACTL ≥ 1.2V. |
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RISET(kΩ) |
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12 |
NC |
No Internal Connection. |
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13 |
EN |
Chip enable pin, when pulled low, chip is in shutdown mode. |
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14, 15, 16 |
LED6, LED7, |
Channel 6 to Channel 8 LED current sink. Leave the pin unconnected if not |
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LED8 |
used. |
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17 |
CREG |
4.7μF capacitor should be placed on this pin to stabilize the 5V output of the |
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internal regulator. This regulator is for chip internal use only. |
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18 |
VCC |
Power supply of the chip. For good bypass, a low ESR capacitor is required. |
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19, 20 |
LX |
PWM boost converter switch node. |
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21, 22, 23, 24, |
GND |
Ground pin of the chip. The exposed pad must be soldered to a large PCB |
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25 (Exposed Pad) |
and connected to GND for maximum power dissipation. |
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DS8561C-00 April 2011 |
www.richtek.com |
3
RT8561C
Absolute Maximum Ratings |
(Note 1) |
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z Supply Voltage, VCC ----------------------------------------------------------------------------------------------------- |
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28V |
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z LX Pin Voltage at Switching Off ---------------------------------------------------------------------------------------- |
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50V |
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z LED1 to LED8 Pin |
--------------------------------------------------------------------------------------------------------- |
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50V |
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z ACTL, EN ------------------------------------------------------------------------------------------------------------------- |
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24V |
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z OVP -------------------------------------------------------------------------------------------------------------------------- |
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−0.3V to 5.5V |
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z Power Dissipation, PD @ TA = 25°C |
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WQFN-24L 4x4 ------------------------------------------------------------------------------------------------------------ |
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1.923W |
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z Package Thermal Resistance |
(Note 2) |
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WQFN-24L 4x4, θJA ------------------------------------------------------------------------------------------------------- |
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52°C/W |
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WQFN-24L 4x4, θJC ------------------------------------------------------------------------------------------------------ |
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7°C/W |
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z Junction Temperature ----------------------------------------------------------------------------------------------------- |
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150°C |
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z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- |
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260°C |
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z Storage Temperature Range -------------------------------------------------------------------------------------------- |
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−65°C to 150°C |
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z ESD Susceptibility (Note 3) |
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HBM (Human Body Mode) ---------------------------------------------------------------------------------------------- |
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2kV |
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MM (Machine Mode) ------------------------------------------------------------------------------------------------------ |
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200V |
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Recommended Operating Conditions (Note 4) |
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z Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- |
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4.5V to 24V |
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z Junction Temperature Range -------------------------------------------------------------------------------------------- |
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−40°C to 125°C |
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z Ambient Temperature Range -------------------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VCC = 17V, TA = 25°C, unless otherwise specified) |
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Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
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Unit |
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Supply Current |
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IVCC |
VC ≤ 0.2V (Switching off) |
-- |
3 |
5 |
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mA |
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VIN Under Voltage Lockout |
VUVLO |
VIN Rising |
-- |
4.2 |
4.5 |
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V |
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Threshold |
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Hysteresis |
-- |
0.3 |
-- |
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Shutdown Current |
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ISHDN |
VEN = 0V |
-- |
-- |
10 |
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μA |
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EN Threshold |
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Logic-High |
VEN_H |
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1.6 |
-- |
5 |
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V |
Voltage |
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Logic-Low |
VEN_L |
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-- |
-- |
0.65 |
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ACTL Threshold |
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Logic-High |
VACTL_H |
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1.3 |
-- |
5 |
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V |
Voltage |
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Logic-Low |
VACTL_L |
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-- |
-- |
0.65 |
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EN Pin Input Current |
IEN |
VEN ≤ 5V |
-- |
-- |
0.1 |
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μA |
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LED Current Programming |
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LED Current |
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ILED |
2V > VLED > 0.6V, RISET = 4.75kΩ |
19 |
20 |
21 |
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mA |
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LEDs Current Matching |
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2V > VLED > 0.6V, RISET = 4.75kΩ |
-- |
-- |
1.5 |
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% |
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Calculating |
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(I(MAX) − I(MIN)) / IAverage x 100% |
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RISET Pin Voltage |
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VRISET |
3.6kΩ ≤ RISET ≤ 9.6kΩ, VACTL > 1.2V |
1.17 |
1.2 |
1.23 |
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V |
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Input Current of ACTL |
IACTL |
VACTL = 1.3V |
-- |
1 |
2 |
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μA |
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VLED Threshold |
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Un-connection |
-- |
0.1 |
-- |
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V |
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To be continued |
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www.richtek.com |
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DS8561C-00 |
April 2011 |
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4
RT8561C
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
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PWM Boost Converter |
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Switching Frequency |
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0.8 |
1 |
1.2 |
MHz |
Minimum On Time |
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-- |
100 |
-- |
ns |
Regulated VLED |
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Highest Voltage LED String |
0.5 |
0.6 |
0.7 |
V |
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Amplifier (gm) Output Current |
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2.4V > VC > 0.2V |
-- |
±15 |
-- |
μA |
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VC Threshold |
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PWM Switch Off |
0.1 |
0.2 |
-- |
V |
LX RDS(ON) |
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-- |
0.3 |
0.5 |
Ω |
LX Current Limit |
ILIM |
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2.5 |
-- |
-- |
A |
OVP & Soft Start |
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OVP Threshold |
VOVP |
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1.1 |
1.2 |
1.3 |
V |
OVP Input Current |
IOVP |
VOVP ≤ 3V |
-- |
-- |
50 |
nA |
Soft Start Current |
ISS |
VSS ≤ 2.5V |
3 |
5 |
8 |
μA |
Thermal Shutdown |
TSD |
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-- |
150 |
-- |
°C |
Temperature |
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Thermal Shutdown Hysteresis |
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-- |
20 |
-- |
°C |
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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 high effective four layers thermal conductivity test board of JEDEC 51-7 thermal measurement standard. The case point of θJC is on the expose pad for the WQFN package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
DS8561C-00 April 2011 |
www.richtek.com |
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