®
RT8577A
High Voltage 4-CH LED Driver
General Description
Features
The RT8577A is an 4-CH LED driver capable of delivering
120mA for each channel. The RT8577A is a current mode
boost converter with an adjustable switching frequency
via the RT pin from 200kHz to 2.1MHz and a wide VIN
range from 5.5V to 40V.
Wide Input Supply Voltage Range : 5.5V to 40V
Adjustable Boost Controller Switching Frequency
from 200kHz to 2.1MHz
Programmable Channel Current
Channel Current Matching : ±1.5%
External Dimming Control
Boost MOSFET Over Current Protection
Automatic LED Open/Short Protection to Avoid
Output Over Voltage
VCC Under Voltage Lockout
Adjustable Over Voltage Protection
Thermal Shutdown Protection
Abnormal Status Indicator for OVP/Short/OTP
Condition
AEC-Q100 Grade 3 Certification
RoHS Compliant and Halogen Free
The PWM output voltage loop selects and regulates the
LED pin with the highest voltage string to 0.6V, hence
allowing voltage mismatches between LED strings. The
RT8577A automatically detects and disconnects any
unconnected and/or broken strings during operation from
PWM loop to prevent VOUT from over voltage. The 1.5%
matched LED currents on all channels are simply
programmed with a resistor. A very high contrast ratio true
digital PWM dimming can be achieved by driving the PWM
pin with a PWM signal.
When an abnormal situation (OVP/short/OTP) occurs, a
status signal will be sent to the system to shut down the
IC.
Applications
Ordering Information
Package Type
QW : WQFN-20L 5x5 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Pin Configuration
(TOP VIEW)
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
RT8577AGQW : Product Number
VC
19
18
17
16
GND
1
15
STATUS
GND
2
14
VCC
GND
3
13
NC
LED3
4
12
CREG
LED4
5
11
DRV
GND
21
6
7
8
9
10
EN
YMDNN : Date Code
SEN
RT8577A
GQW
YMDNN
20
OVP
PWM
ments of IPC/JEDEC J-STD-020.
NC
RoHS compliant and compatible with the current require-
RT
LED1
Richtek products are :
LED2
Note :
RISET
RT8577A
Automotive Infotainment
LCD TV, Monitor Display Backlight
LED Driver Application
General Purpose Constant Current Source
WQFN-20L 5x5
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT8577A
Functional Pin Description
Pin No.
Pin Name
1, 2, 3,
GND
21 (Exposed pad)
4, 5
LED4, LED3
Pin Function
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Channel 3 and channel 4 LED current sinks. Leave the pins unconnected if not
used.
Over-voltage detection input. The Boost converter turns off when VOVP goes
higher than 2V.
6
OVP
7
RISET
LED current set pin. A resistor or a current from DAC on this pin programs the
full LED current.
8
RT
Switching frequency set. Connect a resistor between RT and GND to set the
boost converter switching frequency.
9
EN
Enable control input. When EN is pulled low, the chip will be shut down.
10
SEN
Current sense input. During normal operation, this pin senses the voltage
across the external inductor current sensing resistor for peak current mode
control and also to limit the inductor current during every switching cycle.
11
DRV
Boost converter power switch gate output. This pin drives the external power
N-MOSFET device.
12
CREG
Regulator output for chip internal use only. A 1F capacitor should be placed on
this pin to stabilize the 5V output of the internal regulator.
NC
No internal connection.
14
VCC
Power supply of the chip. For good bypass, a low ESR capacitor close to the pin
is required.
15
STATUS
Status indicator output. This pin will be pulled to low if fault happens.
16
VC
PWM boost converter loop compensation node.
17
PWM
Dimming control input.
19
LED1
Channel 1 LED current sink, leave this pin unconnected if it is not used.
20
LED2
Channel 2 LED current sink, leave this pin unconnected if it is not used.
13, 18
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Function Block Diagram
DRV SEN
OSC
RT
VCC
STATUS
OVP
-
UVLO
S
+
OTP
R
OVP
+
2V
LED Short
R
-
LED1
-
1.2V
+
+
-
Shutdown
+
-
CREG
5V
LDO
VC
5V
VOUT
Regulation
Unit
PWM
…………………
EN
LED4
+
-
+
GND
-
RISET
Operation
The RT8577A integrated a current-mode Boost PWM
controller and 4 LED drivers. When EN and PWM are high
and VIN is higher than the UVLO threshold voltage, the
controller starts operation. In normal operation, the DRV
pin turns high when the gate driver is set by the oscillator
and the DRV pin turns low when the gate driver is reset by
the current comparator. When the DRV pin turns high to
turn on the external MOSFET, the inductor current will
rise up. Once the SEN pin voltage reaches the level of the
VC pin, the current comparator will reset the gate driver
and turn off the MOSFET. The DRV pin is then set to high
again by OSC and repeats in the next switching cycle.
The oscillator frequency can be set by an external resistor
at the RT pin.
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
The output voltage of the Boost converter supports LED
current and regulation voltage at the LEDx pin. The LED
current is set by an external resistor at the RISET pin. A
PWM dimming function is provided to control the LED
brightness through the PWM pin. If OVP, OTP or shorted
LED happens, the STATUS pin will be pulled to low as a
fault indicator.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT8577A
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VCC, STATUS ----------------------------------------------------------------------------------------LED1 to LED4 --------------------------------------------------------------------------------------------------------------PWM, EN, DRV, SEN, VC, RT, CREG, OVP, RISET -------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WQFN-20L 5x5 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WQFN-20L 5x5, θJA -------------------------------------------------------------------------------------------------------WQFN-20L 5x5, θJC ------------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
−0.3V to 45V
−0.3V to 50V
−0.3V to 5.6V
3.54W
28.2°C/W
7.1°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Voltage, VCC -----------------------------------------------------------------------------------------------------LED1 to LED4 --------------------------------------------------------------------------------------------------------------ILED1 to ILED4 ----------------------------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------------------Ambient Temperature Range ---------------------------------------------------------------------------------------------
5.5V to 40V
45V
20mA to 120mA
−40°C to 125°C
−40°C to 105°C
Electrical Characteristics
(VCC = 12V, TA = −40°C to 85°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
1
2
5
mA
0.5
10
30
A
Supply Voltage
Supply Current
IVCC
Switching Off
Shutdown Current
ISHDN
VEN 0.7V
VDD LDO Output
VCREG
4.5
5
VDD LDO Capability
ICREG
30
75
150
VCC UVLO Threshold
VUVLO
VCC rising
3.8
4.5
4.8
Hysteresis
0.1
0.3
0.7
--
EN Threshold
Voltage
Logic-High
VENH
1.5
--
--
Logic-Low
VENL
--
--
0.8
5.5
0.8
V
mA
V
V
LED Current Programming
RISET = 15k, VPWM 1.2V
LED Current Accuracy
76
80
84
mA
--
1.5
3
%
ILED = 80mA
LED Current Matching
(Note5)
ILEDx ILED_AVE
ILED_AVE
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
100%
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
LED1 to LED4 Regulation Voltage
ILED = 80mA
0.75
0.86
1
V
VLED Threshold
No connection
0.05
0.1
0.36
V
0.8
1.2
1.5
V
RISET Pin Voltage
Dimming
Logic-High
VPWMH
1.2
--
--
Logic-Low
VPWML
--
--
0.52
RRT = 20k
1.8
2.1
RRT = Open
50
200
350
kHz
Working
0
40
60
ns
80
--
100
%
0.1
0.5
Gate Driver Source
0.9
2.5
3.5
A
Gate Driver Sink
1.6
3
7
A
1.9
2
2.1
V
PWM Threshold
Voltage
V
PWM Boost Controller
Switching Frequency
Minimum On Time
f SW
(Note 5)
Maximum Duty Cycle
SEN Current Sense Limit
tON
Dmax
(Note 5)
Input current limit
2.4
0.6
MHz
V
OVP, SCP, OTP
OVP Threshold
(Note 5)
VOVP
SCP Threshold
VSCP
LED1 to LED4
6
7
8
V
STATUS Low Voltage
VSTATUS
Open drain at 10mA
0
--
0.5
V
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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
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..
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT8577A
Typical Application Circuit
L1
10µH
VIN
5.5V to 40V
R1
D1
CIN
20µF
CVCC
1µF
MSW
RF1
100
RSENSE
100m
External PWM
Enable
RC
560
CC
0.22µF
10
STATUS
RISET
RT
9 EN
16
:
:
:
:
RSTATUS
100k
15
:
:
: …… :
:
:
:
:
:
:
:
:
COUT
4.7µF x 6
VIN
FLT
7
RISET
9.1k
8
RRT 56k
CREG 12
CREG 1µF
VC
GND
1, 2, 3,
21 (Exposed Pad)
ILED (Note 6)
RISET
120mA
10k
80mA
15k
20mA
68k
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
19
LED1
20
LED2
4
LED3
5
LED4
SEN
11 DRV
RPWM
1k 17
PWM
RENA
1k
ROVP1
100k
RT8577A
CF
1nF
RDRV
5
ROVP2
2.1M
OVP 6
14 VCC
VOUT
45V (MAX)
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Timing Diagram
Power On/Off Sequence
LED driver is without power sequence concern. Mode1, Mode2 and Mode3 are different power sequences respectively.
There is no concern in the above condition.
Mode1 : Delay Time of PWM vs VOUT
VIN
VOUT
EN
100ns
PWM
Mode2 : Delay Time of EN vs VOUT
VIN
VOUT
100µs
EN
PWM
Mode3 : Delay Time of VIN vs VOUT
VIN
UVLO
UVLO
VOUT
EN
PWM
Figure 1. Power On/Off Sequence
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT8577A
Typical Operating Characteristics
LED Current vs. Input Voltage
LED Current vs. PWM Duty Cycle
160
120
100
LED Current (mA)
LED Current (mA)
140
120
LED1
LED2
LED3
LED4
100
80
80
PWM = 200Hz
PWM = 1kHz
PWM = 10kHz
60
40
20
48LEDs, RISET = 10kΩ
VIN = 12V, 48LEDs, RISET = 10kΩ
60
0
8
10
12
14
16
18
20
22
24
26
28
0
10
20
30
40
50
60
70
80
90
Input Voltage (V)
PWM Duty Cycle (%)
Efficiency vs. Input Voltage
Start up with Minimum PWM Duty
100
100
Efficiency (%)
95
90
VOUT
(10V/Div)
85
VIN
(5V/Div)
80
IOUT
(50mA/Div)
75
PWM
(2V/Div)
48LEDs, RISET = 10kΩ
70
8
10
12
14
16
18
20
22
24
26
f = 400Hz, PWM Duty = 1%
Time (50ms/Div)
28
Input Voltage (V)
OVP Protection
LED Short Delay Time
VIN = 12V, Short 3LEDs,
48LEDs, RISET = 10kΩ
OVP
(1V/Div)
OVP Trigger by LED remove,
VIN = 12V, VOUT = 48LEDS
VLEDx
(10V/Div)
VOUT
(5V/Div)
STATUS
(5V/Div)
STATUS
(5V/Div)
DRV
(5V/Div)
DRV
(5V/Div)
Time (100μs/Div)
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
8
IOUT
(100mA/Div)
Time (25μs/Div)
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
LED Short Protection
LED Short Protection
IOUT
(100mA/Div)
IOUT
(100mA/Div)
STATUS
(5V/Div)
Before Short
STATUS
(5V/Div)
VLEDx
(10V/Div)
VLEDx
(10V/Div)
DRV
(5V/Div)
DRV
(5V/Div)
VIN = 12V, Short 3LEDs
After Short
VIN = 12V, Short 3LEDs
Time (2.5ms/Div)
Time (2.5ms/Div)
Power On from EN
Power Off from EN
EN
(2V/Div)
EN
(2V/Div)
DRV
(5V/Div)
DRV
(5V/Div)
I IN
(1A/Div)
I IN
(1A/Div)
VIN = 12V, 48LEDs, RISET = 10kΩ
VIN = 12V, 48LEDs, RISET = 10kΩ
Time (10ms/Div)
Time (25ms/Div)
Power On from VIN
Power Off from VIN
VIN
(10V/Div)
VIN
(10V/Div)
DRV
(5V/Div)
DRV
(5V/Div)
I IN
(1A/Div)
VIN = 12V, 48LEDs, RISET = 10kΩ
Time (10ms/Div)
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
I IN
(1A/Div)
VIN = 12V, 48LEDs, RISET = 10kΩ
Time (25ms/Div)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT8577A
Power On from PWM
Power Off from PWM
PWM
(2V/Div)
PWM
(2V/Div)
DRV
(5V/Div)
DRV
(5V/Div)
I IN
(1A/Div)
I IN
(1A/Div)
VIN = 12V, 48LEDs, RISET = 10kΩ
Time (10ms/Div)
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
VIN = 12V, 48LEDs, RISET = 10kΩ
Time (10ms/Div)
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Application information
The RT8577A is an 4-CH driver controller that delivers well
matched LED current to each channel of LED strings. The
external N-MOSFET current source will accommodate the
power dissipation difference among channels resulting from
the forward voltage difference between the LED strings.
With high speed current source N-MOSFET drivers, the
RT8577A features highly accurate current matching, while
also providing very fast turn-on and turn-off times. This
allows a very narrow minimum on or off pulse. The RT8577A
integrates adjustable switching frequency and provides
circuitry for over temperature, over voltage, under voltage
and current limit protection.
Compensation
The regulator loop can be compensated by adjusting the
external components connected to the VC pin. The VC
pin is the output of the internal error amplifier. The
compensation capacitor will adjust the integrator zero to
maintain stability and the resistor value will adjust the
frequency integrator gain for fast transient response.
Typical values of the compensation components are RC =
560Ω, CC = 0.22μF.
LED Connection
The RT8577A equips 4-CH LED drivers and each channel
supports up to 15 LEDs. The LED strings are connected
from the output of the boost converter to pin LEDx (x = 1
to 4) respectively. If one of the LED channel is not in use,
the LED pin should be opened directly.
Setting and Regulation of LED current
The LED current can be calculated by the following
equation :
1200
ILED
40mA < ILED 120mA
RISET
ILED
1360
20mA < ILED 40mA
RISET
where RISET is the resistor between the RISET pin and
GND. This setting is the reference for the LED current at
pin LEDx and represents the sensed LED current for each
string. The DC/DC converter regulates the LED current
according to the setting.
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
Over Voltage Protection
The RT8577A integrates Over Voltage Protection (OVP) .
When the voltage at the OVP pin rises above the threshold
voltage of approximately 2V, the internal switch will be
turned off and STATUS pin will be pulled to low. The internal
switch will be turned on again once the voltage at the
OVP pin returns to normal range. The output voltage can
be clamped at a certain voltage level and can be calculated
by the following equations :
R
VOUT(OVP) = VOVP 1 + OVP2
ROVP1
where ROVP1 and ROVP2 are the resistors in the resistive
voltage divider connected to the OVP pin. If at least one
string is in normal operation, the controller will
automatically ignore the open strings and continue to
regulate the current for the strings in normal operation.
Suggested value for ROVP2 is up to 3.6MΩ to prevent loading
effect.
LED Short Circuit Protection
The RT8577A integrates LED Short Circuit Protection
(SCP). If one of the LED1 to LED4 pin voltages exceeds
a threshold of approximately 7V during normal operation,
the STATUS pin will be pulled low for a fault signal.
STATUS
The RT8577A provides a fault status indicator with an open
drain STATUS pin. If fault condition (LED Short/OVP/OTP)
occurs, the STATUS will be reset after VIN or EN is reapplied.
Setting the Switching Frequency
The RT8577A switching frequency is programmable from
200kHz to 2.1MHz by adjusting the oscillator resistor,
RRT. The switching frequency can be calculated by the
following equation :
fSW 200k +
38 109
RRT
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT8577A
Current Limit Protection
Over Temperature Protection
The RT8577A can sense the RSENSE voltage between the
SEN pin and GND to achieve over current protection. The
boost converter senses the inductor current during the on
period. The duty cycle depends on the current signal and
internal slope compensation compared with the error
signal. The external switch will be turned off when the
current signal is larger than the internal slope
compensation. In the off period, the inductor current will
decrease until the internal switch is turned on by the
oscillator. The current limit value can be calculated by the
following equation :
0.5V
Current Limit (A)
RSENSE
The RT8577A has over temperature protection function to
prevent the IC from overheating due to excessive power
dissipation. The IC will shut down and the STATUS pin
will be pulled low when junction temperature exceeds
150°C. Main converter starts switching after junction
temperature cools down by approximately 20°C.
Inductor Selection
The value of the inductance, L, can be approximated by
the following equation, where the transition is from
Discontinuous Conduction Mode (DCM) to Continuous
Conduction Mode (CCM) :
2
L=
Brightness Control
The RT8577A features a digital dimming control scheme.
A very high contrast ratio true digital PWM dimming is
achieved by driving the PWM pin with a PWM signal. The
recommended PWM frequency is 100Hz to 10kHz, but
the LED current cannot be 100% proportional to duty cycle,
especially for high frequency and low duty ratio because
of physical limitation caused by inductor rising time.
Please refer to Table 1.
Table 1.
Dimming Frequency (Hz) Duty (Min.)
100 < f PWM 500
0.2%
500 < f PWM 1k
0.4%
1k < f PWM 2k
0.8%
2k < f PWM 5k
1.5%
5k < f PWM 10k
3%
Duty (Max.)
100%
100%
100%
100%
100%
Note : The minimum duty in Table 1 is based on the application
circuit and does not consider the deviation of current linearity.
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
D 1 D VOUT
2 f IOUT
The duty cycle can be calculated as the following
equation :
V
VIN
D = OUT
VOUT
where VOUT is the maximum output voltage, VIN is the
minimum input voltage, f is the operating frequency, and
IOUT is the sum of current from all LED strings.
The boost converter operates in DCM over the entire input
voltage range when the inductor value is less than this
value, L. With an inductance greater than L, the converter
operates in CCM at the minimum input voltage and may
be discontinuous at higher voltages.
The inductor must be selected with a saturated current
rating that is greater than the peak current as provided by
the following equation :
V
I
V D T
IPEAK = OUT OUT IN
η VIN
2L
where η is the efficiency of the power converter.
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Schottky diodes are recommended for most applications
because of their fast recovery time and low forward voltage.
Power dissipation, reverse voltage rating, and pulsating
peak current are important parameters for consideration
when making a Schottky diode selection. Make sure that
the diode's peak current rating exceeds IPEAK and reverse
voltage rating exceeds the maximum output voltage.
Capacitor Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
general applications, six 4.7μF ceramic capacitors are
sufficient. A value higher or lower may be used depending
on the noise level from the input supply and the input
current to the converter.
packages, the thermal resistance, θJA, is 28.2°C/W on a
standard JEDEC 51-7 four-layer thermal test board. The
maximum power dissipation at TA = 25°C can be calculated
by the following formula :
PD(MAX) = (125°C − 25°C / (28.2°C/W) = 3.54W for
WQFN-20L 5x5 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 2 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
4.0
Maximum Power Dissipation (W)1
Diode Selection
It is recommended to choose a ceramic capacitor based
on the output voltage ripple requirements. The minimum
value of the output capacitor, COUT, can be calculated by
the following equation :
COUT =
IOUT D
VOUT f
Four-Layer PCB
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
where ΔVOUT is the peak-to-peak ripple voltage at the
output.
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum Power Dissipation
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
Layout Considerations
Careful PCB layout is very important for designing
switching power converter circuits. The following layout
guidelines should be strictly followed for best performance
of the RT8577A.
The power components L1, D1, CIN, COUT must be placed
as close as possible to the IC to reduce current loop.
The PCB trace between power components must be as
short and wide as possible.
The compensation circuit should be kept away from
the power loops and shielded with a ground trace to
prevent any noise coupling. Place the compensation
components, RC and CC, as close as possible to pin 9.
The exposed pad of the chip should be connected to
ground plane for thermal consideration.
PD(MAX) = (TJ (MAX) − TA) / θJA
where TJ (MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C and TA is the
ambient temperature. The junction to ambient thermal
resistance, θJA, is layout dependent. For WQFN-20L 5x5
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8577A
OVP Protection
VIN
PWM
Delay time 50µs
STATUS
Status latch until EN goes low
VOUT
OVP
2V
OVP
EN
SW Frequency = 2.1MHz
Time
DRV
Short Protection
VIN
PWM
ILEDX(1)
10µs
10µs
ILEDX(2)
Delay time 50µs
STATUS
Status latch until EN goes low
VLEDX(1)
LED SHORT
VLEDX(2)
EN
7V
SW Frequency = 2.1MHz
DRV
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
Time
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
OTP Function
Thermal
130°C
150°C
150°C
130°C
STATUS
VOUT
DRV
Protection Functions
Description
LED Short
Detect VLEDx voltage.
Triggered if VLEDx 7V.
Protection
Behavior
V
If one of LED1 to LED4 pin voltages exceeds a
threshold of approximately 7V during normal
operation, the STATUS pin will be pulled to low
for a fault signal. Internal switching does not stop.
OVP
Use OVP pin voltage for
detection. Triggered if OVP
pin voltage 2V.
V
OTP
Triggered if TJ 150C
V
STATUS pin is used as fault
indicator. Fault and pull low.
V
Fault Indicator
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
DS8577A-02 April 2020
The internal switch will be turned off and
STATUS pin will be pulled to low.
The Internal switch will be turned on again once
the voltage at the OVP pin returns to normal
range.
The IC will shut down and the STATUS pin will
be pulled to low when junction temperature
exceeds 150C and IC returns to normal
operation when temperature falls to 130C.
If fault condition (LED short, OVP or OTP)
occurs, the STATUS pin will be pulled to low.
It will be reset after VIN or EN is re-applied.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT8577A
Locate the CVCC as close to
VCC as possible.
CVCC
CC
PGND
LED1
NC
PWM
VC
20
19
18
17
16
VIN
GND
1
15
GND
2
14
STATUS
R1
VCC
GND
3
13
NC
LED3
4
12
CREG
LED4
5
11
DRV
GND
21
VIN
L1
RISET
9
D1
VOUT
MSW
10
CF
SEN
8
EN
7
RISET
RT
OVP
6
COUT
RDRV
RF1
AGND
CIN
+
Separate power ground (PGND) and
analog ground (AGND). Connect AGND
and PGND islands at a single end. Make
sure there are no other connections
between these separate ground planes.
The PGND should be wide and short
enough to connect ground plane.
LED2
RC
RSENSE
Place the power components as
Close as possible. The traces
should be wide and short especially
for the high current loop.
PGND
RRT
AGND
The exposed pad of the chip
should be connected to ground
plane for thermal consideration.
The compensation circuit and RISET resistor
should be kept away from the power loops and
should be shielded with a ground trace to prevent
any noise coupling.
Figure 3. PCB Layout Guide
Copyright © 2020 Richtek Technology Corporation. All rights reserved.
www.richtek.com
16
is a registered trademark of Richtek Technology Corporation.
DS8577A-02 April 2020
RT8577A
Outline Dimension
1
2
DETAIL A
Pin #1 ID and Tie Bar Mark
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.250
0.350
0.010
0.014
D
4.900
5.100
0.193
0.201
D2
3.100
3.200
0.122
0.126
E
4.900
5.100
0.193
0.201
E2
3.100
3.200
0.122
0.126
e
L
0.650
0.500
0.026
0.600
0.020
0.024
W-Type 20L QFN 5x5 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. 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.
DS8577A-02 April 2020
www.richtek.com
17
工商网监
湘ICP备2023018690号
