RICHCO RT8525

®
RT8525
Boost Controller with Dimming Control
General Description
Features
The RT8525 is a wide input operating voltage range step
up controller. High voltage output and large output current
are feasible by using an external N-MOSFET. The RT8525
input operating range is from 4.5V to 29V.
z
Programmable Soft-Start Time
z Programmable Boost SW Frequency from 50kHz to
600kHz
z Output Over Voltage Protection
z Output Under Voltage Protection
z 14-Lead SOP Package
z RoHS Compliant and Halogen Free
z
The RT8525 is an optimized design for wide output voltage
range applications. The output voltage of the RT8525 can
be adjusted by the FB pin. The PWMI pin can be used as
a digital input, allowing WLED brightness control with a
logic-level PWM signal.
Applications
Ordering Information
z
RT8525
z
Note :
VIN Range : 4.5V to 29V
Package Type
S : SOP-14
Lead Plating System
G : Green (Halogen Free and Pb Free)
LCD TV, Monitor Display Backlight
LED Driver Application
Pin Configurations
(TOP VIEW)
VDC
VIN
COMP
SS
FSW
AGND
PWMI
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
14
2
13
3
12
4
11
5
10
6
9
7
8
DRV
PGND
EN
ISW
OOVP
FB
FAULT
SOP-14
RT8525GS : Product Number
RT8525
GSYMDNN
YMDNN : Date Code
Typical Application Circuit
VIN
24V
CIN
100µF
2 VIN
CVIN
1µF
RC
33k
CC1
27nF
L1
33µH
RT8525
14
DRV
1
VDC
CDC
1µF
3 COMP
CC2
RSW
56k
5 FSW
4 SS
CSS
0.33µF
Chip Enable
12 EN
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8525-01 March 2012
D1
ISW
PGND
RSLP
11 2.4k
13
FB 9
7
PWMI
RFLT
8 100k
FAULT
OOVP 10
AGND 6
M1
RS
50m
RFB1
117k
PWMI
12V
COVP
VOUT
50V
COUT
100µF x 2
ROVP1
150k
RFB2
3k
ROVP2
6k
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1
RT8525
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VDC
Output of Internal Pre-Regulator.
2
VIN
IC Power Supply.
3
COMP
Compensation for Error Amplifier. Connect a compensation network to ground.
4
SS
External Capacitor to Adjust Soft-Start Time.
5
FSW
6
AGND
Frequency Adjust Pin. This pin allows setting the switching frequency with a resistor
from 50kHz to 600kHz.
Analog Ground.
7
PWMI
External Digital Input for Dimming Function.
8
FAULT
Open Drain Output for Fault Detection.
9
FB
Feedback to Error Amplifier Input.
10
OOVP
Sense Output Voltage for Over Voltage Protection and Under Voltage Protection.
11
ISW
External MOSFET Switch Current Sense Pin. Connect the current sense resistor
between the external N-MOSFET switch and ground.
12
EN
Chip Enable (Active High).
13
PGND
Power Ground of Boost Controller.
14
DRV
Drive Output for the N-MOSFET.
Function Block Diagram
FSW
VIN
VDC
UVLO
+
OTP
OOVP/OUVP
Logic
12V LDO
OSC
+
OC
-
EN
PWMI
PGND
S
Q
R
Q
+
-
DRV
Blanking
VOS
PWM
Controller
2.5V
0.4V
+
-
FAULT
Protection
OOVP
+
-
FAULT
0.1V
-
+
EA
-
AGND
4µA
ISW
1.25V
FB
COMP
SS
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is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
RT8525
Absolute Maximum Ratings
z
z
z
z
z
z
z
z
z
(Note 1)
VIN to GND -----------------------------------------------------------------------------------------------------------------VDC, DRV, FAULT to GND ----------------------------------------------------------------------------------------------EN, COMP, SS, FSW, FB, OOVP, ISW, PWMI to GND --------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-14 ---------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-14 , θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM -------------------------------------------------------------------------------------------------------------------------MM ----------------------------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
z
z
z
−0.3V to 32V
−0.3V to 13.2V
−0.3V to 6V
1.000W
100°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 29V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 21V, VOUT = 50V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max Unit
Input Power Supply
Quiescent Current
IQ
No Switching, RSW = 56kΩ
--
1.3
2
mA
Shutdown Current
Under Voltage Lockout
Threshold
Under Voltage Lockout
Hysteresis
12V Regulator
I SHDN
VEN = 0V
--
10
--
μA
VUVLO
VIN Rising
--
3.8
--
V
--
500
--
mV
11.4
12
12.6
V
--
500
--
mV
--
270
--
mA
Logic-High VIH
2
--
--
Logic-Low
--
--
0.8
ΔVUVLO
Regulator Output Voltage
VDC
Dropout Voltage
VDROP
13.5V < VIN < 16V, 1mA < I LOAD < 100mA
16V < VIN < 20V, 1mA < I LOAD < 50mA
20V < VIN < 29V, 1mA < I LOAD < 20mA
VIN − VDC, VIN = 12V, I LOAD = 100mA
Short-Circuit Current Limit
I SC
VDC Short to GND
Control Input
EN Threshold
Voltage
EN Sink Current
Sleeping
Mode
Shutdown Delay
Shutdown
Mode
VIL
I IH
VEN = 5V
--
5
--
μA
t SLEEP
RSW = 56kΩ, EN = L, 12V Regular Shutdown
55
--
--
ms
t SHDN
RSW = 56kΩ, EN = L, IC Shutdown
110
--
--
ms
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8525-01 March 2012
V
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3
RT8525
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
200
--
kHz
--
250
--
ns
90
--
--
%
1.225
1.25
1.275
V
ISLOPE, PK
--
50
--
μA
ISS
3
4
5
μA
Boost Controller
Switching Frequency
f SW
Minimum On-Time
tMON
Maximum Duty
D MAX
Feedback Voltage
VFB
R SW = 56kΩ
Switching
Slope Compensation
Peak Magnitude of Slope
Compensation Current
Soft-Start
Soft-Start Current
Gate Driver
R DS(ON)_N
ISINK = 100mA (N-MOSFET)
--
1
--
Ω
R DS(ON)_P
ISOURCE = 100mA (P-MOSFET)
--
1.5
--
Ω
Peak Sink Current
IPEAKsk
C LOAD = 1nF
--
2.2
--
A
Peak Source Current
IPEAKsr
C LOAD = 1nF
--
2.55
--
A
Rise Time
tr
C LOAD = 1nF
--
6
--
ns
Fall Time
tf
C LOAD = 1nF
--
5
--
ns
DRV On-Resistance
PWM Dimming Control
PWMI
Threshold
Voltage
Logic-High
VPWMI_H
2
--
--
Logic-Low
VPWMI_L
--
--
0.8
--
0.4
--
V
V
Protection Function
OCP Threshold
VOCP
Including Slope Compensation Magnitude
VOUT OVP Threshold
VOVP
2.375
2.5
2.625
V
VOUT UVP Threshold
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
VUVP
--
0.1
--
V
TSD
--
150
--
°C
ΔTSD
--
50
--
°C
Note 1. Stresses beyond those listed “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 low effective thermal conductivity single-layer test board per JEDEC 51-3.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions..
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is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
RT8525
Typical Operating Characteristics
Quiescent Current vs. Temperature
3.0
2.5
2.5
Quiescent Current (mA)
Quiescent Current (mA)
Quiescent Current vs. Input Voltage
3.0
2.0
1.5
1.0
0.5
No Switching
9
14
19
24
1.5
1.0
0.5
No Switching
0.0
0.0
4
2.0
-50
29
-25
0
Feedback Voltage vs. Input Voltage
75
100
125
Feedback Voltage vs. Temperature
1.5
1.5
1.4
1.4
Feedback Voltage (V)
Feedback Voltage (V)
50
Temperature (°C)
Input Voltage (V)
1.3
1.2
1.1
1.0
1.3
1.2
1.1
1.0
4
9
14
19
24
29
-50
-25
0
25
50
75
100
125
Temperature (°C)
Input Voltage (V)
Switching Frequency vs. Temperature
Boost Efficiency vs. Load Current
300
100
260
90
Efficiency(%)
Switching Frequency (kHz)1
25
220
180
140
80
70
60
RSW = 56kΩ
100
VIN = 24V, VOUT = 50V
50
-50
-25
0
25
50
75
100
Temperature (°C)
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8525-01 March 2012
125
0
0.4
0.8
1.2
1.6
2
Load Current (A)
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RT8525
Applications Information
The RT8525 is a wide input operating voltage range step
up controller. High voltage output and large output current
are feasible by using an external N-MOSFET. The
protection functions include output over voltage, output
under voltage, over temperature and current limiting
protection.
Boost Output Voltage Setting
The regulated output voltage is set by an external resistor
divider according to the following equation :
R
VOUT = VFB × ⎛⎜ 1+ FB1 ⎞⎟ , where VFB = 1.25V (typ.)
⎝ RFB2 ⎠
The recommended value of RFB2 should be at least 1kΩ
for saving sacrificing. Moreover, placing the resistor divider
as close as possible to the chip can reduce noise
sensitivity.
Boost Switching Frequency
The RT8525 boost driver switching frequency is able to
be adjusted by a resistor RSW ranging from 18kΩ to
220kΩ. The following figure illustrates the corresponding
switching frequency within the resistor range.
Switching Frequency vs. RSW
600
f SW (kHz)
500
400
300
200
100
VIN = 24V, VOUT = 50V, COUT = 100μF x 2, L1 = 33μH,
while the recommended value for compensation is as
follows : RC = 33kΩ, CC1 = 27nF.
Soft-Start
The soft-start of the RT8525 can be achieved by connecting
a capacitor from the SS pin to GND. The built-in soft-start
circuit reduces the start-up current spike and output
voltage overshoot. The external capacitor charged by an
internal 4μA constant charging current determines the softstart time. The SS pin limits the rising rate of the COMP
pin voltage and thereby limits the peak switch current.
The soft-start interval is set by the soft-start capacitor
according to the following equation :
tSS ≅ CSS × 5 × 105
A typical value for the soft-start capacitor is 0.33μF. The
soft-start capacitor is discharged when EN voltage falls
below its threshold after shutdown delay or UVLO occurs.
Slope Compensation and Current Limiting
A slope compensation is applied to avoid sub-harmonic
oscillation in current-mode control. The slope
compensation voltage is generated by the internal ramp
current flow through a slope compensation resistor RSLP.
The inductor current is sensed by the sensing resistor
RS. Both of them are added and presented on the ISW
pin. The internal ramp current is rising linearly form zero
at the beginning of each switching cycle to 50μA in
maximum on-time of each cycle. The slope compensation
resistor RSLP can be calculated by the following equation :
( VOUT − VIN ) × RS
RSLP >
2 × L × 50μ × fSW
where RS is current sensing resistor, L is inductor value,
0
0
50
100
150
200
250
RSW (kΩ)
Figure 1. Boost Switching Frequency
Boost Loop Compensation
The voltage feedback loop can be compensated by an
external compensation network consisted of RC, CC1 and
CC2. Choose RC to set high frequency gain for fast
transient response. Select CC1 and CC2 to set the zero
and pole to maintain loop stability. For typical application,
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6
and fSW is boost switching frequency.
The current flow through inductor during charging period
is detected by a sensing resistor RS. Besides, the slope
compensation voltage also attributes magnitude to ISW.
As the voltage at the ISW pin is over 0.4V, the DRV will
be pulled low and turn off the external N-MOSFET. So
that the inductor will be forced to leave charging stage
and enter discharging stage to prevent over current. The
current limiting can be calculated by the following equation:
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DS8525-01 March 2012
RT8525
RS <
0.4 − DMAX × RSLP × 50μ
IL, PK
be under 0.25V. Then the protection function will perform
action 2 to turn off the driver. When protection function is
released, the RT8525 will re-start.
where IL, PK is peak inductor current, and DMAX is maximum
duty.
On the other hand, if the triggered protection is OOVP,
the voltage at node A will be decided by voltage divider
composed of RFLT and the internal 8kΩ resistor. This
voltage must be designed between 0.25V and 1.25V by
choosing RFLT appropriately. Once the OOVP turns on the
Switch 2, the divided FAULT voltage will activate action 1
to turn off the driver without resetting soft-start. Therefore,
when protection function OOVP is released, the RT8525
will be in normal operation.
Output Over Voltage Protection
The output voltage can be clamped at the voltage level
determined by the following equation :
R
VOUT (OOVP) = VOOVP × ⎛⎜ 1+ OVP1 ⎞⎟ ,
R
OVP2 ⎠
⎝
where VOOVP = 2.5V (typ.)
where ROVP1 and ROVP2 are the voltage divider connected
to the OOVP pin.
Power MOSFET Selection
Fault Protection
For the applications operating at high output voltage,
switching losses dominate the overall power loss.
Therefore, the power N-MOSFET switch is typically
chosen for drain voltage, VDS, rating and low gate charge.
Consideration of switch on-resistance RDS(ON) is usually
The FAULT pin will be pulled low once a protection is
triggered, and a suitable pulled-high RFLT is required. The
suggested RFLT is 100kΩ if the pulled-high voltage was
12V. The following figure illustrates the fault protection
function block. If one of the OUVP and OTP occurs, the
switch 1 will be turned on, and the voltage at node A will
secondary. The VDC regulator in the RT8525 has a fixed
output current limit to protect the IC and provide 12V DRV
voltage for N-MOSFET switch gate driver.
12V
RFLT
100k
FAULT
8k
OUVP, OTP
Action 1
1.25V Node A - Comparator 1
+
+
OOVP
Switch 1
Switch 2
+
+
0.25V
-
Action 2
Comparator 2
Figure 2. Fault Protection Function Block
Inductor Selection
fsw is the operating frequency,
The boundary value of the inductance L between
Discontinuous Conduction Mode (DCM) and Continuous
Conduction Mode (CCM) can be approximated by the
following equation :
IOUT is the sum of current from all LED strings,
2
D × (1− D ) × VOUT
2 × fSW × IOUT
where
L=
VOUT is the maximum output voltage,
VIN is the minimum input voltage,
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8525-01 March 2012
and D is the duty cycle calculated by the following
equation :
V
− VIN
D = OUT
VOUT
The boost converter operates in DCM over the entire input
voltage range if the inductor value is less than the boundary
value L. With an inductance greater than L, the converter
operates in CCM at the minimum input voltage and may
transit to DCM at higher voltages. The inductor must be
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7
RT8525
selected with a saturated current rating greater than the
peak current provided by the following equation :
ILPK =
VOUT × IOUT VIN × D × T
+
2×L
η × VIN
ΔIL
Input Current
Inductor Current
where η is the efficiency of the power converter.
Output Current
Diode Selection
Time
Schottky diodes are recommended for most applications
because of their fast recovery time and low forward voltage.
The power dissipation, reverse voltage rating and pulsating
peak current are the important parameters for Schottky
diode selection. Make sure that the diode's peak current
rating exceeds ILPK, and reverse voltage rating exceeds
the maximum output voltage.
Capacitor Selection
Output ripple voltage is an important index for estimating
the performance. This portion consists of two parts, one
is the product of input current and ESR of output capacitor,
another part is formed by charging and discharging
process of output capacitor. Refer to figure 3, evaluate
ΔVOUT1 by ideal energy equalization. According to the
definition of Q, the Q value can be calculated as following
equation :
⎡
⎤ V
Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥ × IN
2 ⎣⎝
2
2
⎠ ⎝
⎠ ⎦ VOUT
× 1 = COUT × ΔVOUT1
fSW
where fSW is the switching frequency, and ΔIL is the
inductor ripple current. Move COUT to the left side to
estimate the value of ΔVOUT1 as the following equation :
ΔVOUT1 =
D × IOUT
η × COUT × fSW
Finally, by taking ESR into consideration, the overall output
ripple voltage can be determined as the following
equation :
ΔVOUT = IIN × ESR +
D × IOUT
η × COUT × fSW
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8
(1-D)TS
Output Ripple
Voltage (ac)
Time
ΔVOUT1
Figure 3. The Output Ripple Voltage without the
Contribution of ESR
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 :
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. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOP-14 packages, the thermal resistance, θJA, is 100°C/
W on a standard JEDEC 51-3 single-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) / (100°C/W) = 1.000W for
SOP-14 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 4 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
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RT8525
Maximum Power Dissipation (W)1
1.1
Layout Considerations
Single-Layer PCB
1.0
PCB layout is very important for designing switching power
converter circuits. The following layout guides should be
strictly followed for best performance of the RT8525.
0.9
0.8
0.7
0.6
`
The power components L1, D1, CIN, COUT, M1 and RS
must be placed as close as possible to reduce current
loop. The PCB trace between power components must
be as short and wide as possible.
`
Place components RFB1, RFB2, ROVP1 and ROVP2 close
to IC as possible. The trace should be kept away from
the power loops and shielded with a ground trace to
prevent any noise coupling.
`
The compensation circuit should be kept away from
the power loops and should be shielded with a ground
trace to prevent any noise coupling. Place the
compensation components to the COMP pin as close
as possible, no matter the compensation is RC, CC1 or
0.5
0.4
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 4. Derating Curve of Maximum Power Dissipation
CC2.
Place the power components as close as possible. The traces
should be wide and short especially for the high-current loop.
The compensation circuit
PGND
should be kept away from
the power loops and should
be shielded with a ground
trace to prevent any noise
coupling.
14
VDC
2
13
VIN
3
12
COMP
4
11
RC
SS
CC2
5
10
FSW
CC1
9
6
AGND
7
8
PWMI
VIN
VIN
CIN
D1
L1
VOUT
COUT
DRV
M1
PGND
PGND
RS
EN R
SLP
ISW
ROVP2
OOVP
FB
ROVP1
RFB2 AGND
FAULT
RFB1
AGND is suggested
that connect to PGND
from the sense resistor
RS for better stability.
VOUT
The feedback voltage divider resistors must near the
feedback pin. The divider center trace must be
shorter and avoid the trace near any switching nodes.
Figure 5. PCB Layout Guide
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RT8525
Outline Dimension
H
A
M
J
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
8.534
8.738
0.336
0.344
B
3.810
3.988
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.508
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.178
0.254
0.007
0.010
I
0.102
0.254
0.004
0.010
J
5.791
6.198
0.228
0.244
M
0.406
1.270
0.016
0.050
14–Lead SOP Plastic Package
Richtek Technology Corporation
5F, No. 20, Taiyuen 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.
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DS8525-01 March 2012