RT8525 [RICHCO]
Boost Controller with Dimming Control; 升压控制器，调光控制
| 型号： | RT8525 |
| 厂家： | 
RICHCO, INC. |
| 描述： | Boost Controller with Dimming Control |
| 文件： | 总10页 (文件大小：222K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
®
RT8525
Boost Controller with Dimming Control
General Description
Features
z VIN Range : 4.5V to 29V
The RT8525 is a wide input operating voltage range step
up controller. High voltage output and large output current
are feasible by using an externalN-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
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.
z RoHS Compliant and Halogen Free
Applications
z LCD TV, Monitor Display Backlight
Ordering Information
RT8525
z LEDDriverApplication
Package Type
S : SOP-14
Pin Configurations
Lead Plating System
G : Green (Halogen Free and Pb Free)
(TOP VIEW)
Note :
14
VDC
VIN
COMP
SS
FSW
AGND
PWMI
DRV
PGND
EN
ISW
OOVP
FB
Richtek products are :
2
3
4
5
6
7
13
12
11
10
9
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
8
FAULT
Marking Information
SOP-14
RT8525GS : Product Number
RT8525
GSYMDNN
YMDNN : Date Code
Typical Application Circuit
L1
33µH
D1
V
V
50V
IN
OUT
24V
C
C
OUT
IN
RT8525
100µF x 2
100µF
14
11
2
1
VIN
M1
DRV
R
SLP
C
VIN
2.4k
1µF
VDC
ISW
C
1µF
DC
R
S
50m
3
COMP
R
13
FB1
117k
PGND
C
C2
R
C
9
7
33k
C
FB
5
4
PWMI
PWMI
12V
R
3k
C1
FSW
SS
FB2
R
FLT
27nF
R
150k
OVP1
R
100k
SW
8
FAULT
OOVP
56k
C
SS
10
0.33µF
R
OVP2
6k
6
C
12
OVP
AGND
Chip Enable
EN
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
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1
RT8525
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
2
3
4
VDC
Output of Internal Pre-Regulator.
IC Power Supply.
VIN
COMP
SS
Compensation for Error Amplifier. Connect a compensation network to ground.
External Capacitor to Adjust Soft-Start Time.
Frequency Adjust Pin. This pin allows setting the switching frequency with a resistor
from 50kHz to 600kHz.
5
FSW
6
7
AGND
PWMI
Analog Ground.
External Digital Input for Dimming Function.
Open Drain Output for Fault Detection.
Feedback to Error Amplifier Input.
8
FAULT
FB
9
10
OOVP
Sense Output Voltage for Over Voltage Protection and Under Voltage Protection.
External MOSFET Switch Current Sense Pin. Connect the current sense resistor
between the external N-MOSFET switch and ground.
11
ISW
12
13
14
EN
Chip Enable (Active High).
PGND
DRV
Power Ground of Boost Controller.
Drive Output for the N-MOSFET.
Function Block Diagram
FSW
+
-
0.1V
2.5V
VIN
UVLO
OTP
OOVP/OUVP
Logic
OOVP
DRV
+
-
VDC
12V LDO
FAULT
Protection
OSC
S
R
Q
Q
FAULT
+
OC
EN
PWMI
PGND
AGND
0.4V
-
Blanking
ISW
V
OS
+
-
-
PWM
Controller
+
1.25V
EA
FB
-
COMP
4µA
SS
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
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2
RT8525
Absolute Maximum Ratings (Note 1)
z VINtoGND------------------------------------------------------------------------------------------------------------------ −0.3V to 32V
z VDC, DRV, FAULT toGND----------------------------------------------------------------------------------------------- −0.3V to 13.2V
z EN, COMP, SS, FSW, FB, OOVP, ISW, PWMI to GND--------------------------------------------------------- −0.3V to 6V
z Power Dissipation, PD @ TA = 25°C
SOP-14 ---------------------------------------------------------------------------------------------------------------------- 1.000W
z Package Thermal Resistance (Note 2)
SOP-14 , θJA ---------------------------------------------------------------------------------------------------------------- 100°C/W
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C
z Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM -------------------------------------------------------------------------------------------------------------------------- 2kV
MM---------------------------------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 29V
z Junction Temperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 21V, VOUT = 50V, TA = 25°C, unless otherwise specified)
Parameter
Input Power Supply
Quiescent Current
Shutdown Current
Symbol
Test Conditions
Min Typ Max Unit
I
No Switching, R = 56kΩ
--
--
1.3
10
2
mA
Q
SW
I
V
EN
= 0V
--
μA
SHDN
Under Voltage Lockout
Threshold
Under Voltage Lockout
Hysteresis
V
V
IN
Rising
--
--
3.8
--
--
V
UVLO
ΔV
500
mV
UVLO
12V Regulator
13.5V < V < 16V, 1mA < I
< 100mA
LOAD
IN
Regulator Output Voltage
V
11.4 12 12.6
V
16V < V < 20V, 1mA < I
< 50mA
LOAD
DC
IN
20V < V < 29V, 1mA < I
< 20mA
LOAD
IN
Dropout Voltage
V
V
− V , V = 12V, I = 100mA
LOAD
--
--
500
270
--
--
mV
mA
DROP
IN
DC IN
Short-Circuit Current Limit
Control Input
I
VDC Short to GND
SC
Logic-High V
2
--
--
--
--
5
--
0.8
--
EN Threshold
Voltage
IH
IL
V
Logic-Low
V
I
EN Sink Current
V
EN
= 5V
μA
IH
Sleeping
Mode
Shutdown
Mode
t
t
R
= 56kΩ, EN = L, 12V Regular Shutdown 55
--
--
--
--
ms
SLEEP
SHDN
SW
SW
Shutdown Delay
R
= 56kΩ, EN = L, IC Shutdown
110
ms
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
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3
DS8525-01 March 2012
RT8525
Parameter
Symbol
Test Conditions
Min
Typ
Max Unit
Boost Controller
Switching Frequency
Minimum On-Time
Maximum Duty
f
t
R
= 56kΩ
SW
--
--
200
250
--
--
--
--
kHz
ns
%
SW
MON
D
Switching
90
MAX
Feedback Voltage
Slope Compensation
V
I
1.225 1.25 1.275
V
FB
Peak Magnitude of Slope
Compensation Current
--
3
50
4
--
5
μA
μA
SLOPE, PK
Soft-Start
Soft-Start Current
Gate Driver
I
SS
R
R
I
I
= 100mA (N-MOSFET)
= 100mA (P-MOSFET)
SOURCE
--
--
--
--
--
--
1
1.5
2.2
2.55
6
--
--
--
--
--
--
Ω
Ω
DS(ON)_N
SINK
DRV On-Resistance
DS(ON)_P
Peak Sink Current
Peak Source Current
Rise Time
I
I
t
t
C
C
C
C
= 1nF
= 1nF
= 1nF
= 1nF
A
PEAKsk
LOAD
LOAD
LOAD
LOAD
A
PEAKsr
ns
ns
r
f
Fall Time
5
PWM Dimming Control
PWMI
Threshold
Logic-Low
Voltage
Logic-High
V
V
2
--
--
--
PWMI_H
PWMI_L
V
--
0.8
Protection Function
OCP Threshold
V
V
V
Including Slope Compensation Magnitude
--
0.4
--
V
V
V
OCP
OVP
UVP
V
V
OVP Threshold
UVP Threshold
2.375 2.5 2.625
OUT
--
--
0.1
--
--
OUT
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
T
150
°C
°C
SD
ΔT
--
50
--
SD
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..
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
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4
RT8525
Typical Operating Characteristics
Quiescent Current vs. Temperature
Quiescent Current vs. Input Voltage
3.0
2.5
2.0
1.5
1.0
0.5
0.0
3.0
2.5
2.0
1.5
1.0
0.5
No Switching
24 29
No Switching
0.0
-50
-25
0
25
50
75
100
125
4
9
14
19
Temperature (°C)
Input Voltage (V)
Feedback Voltage vs. Input Voltage
Feedback Voltage vs. Temperature
1.5
1.4
1.3
1.2
1.1
1.0
1.5
1.4
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
260
220
180
140
100
100
90
80
70
60
50
RSW = 56kΩ
VIN = 24V, VOUT = 50V
1.2 1.6 2
-50
-25
0
25
50
75
100
125
0
0.4
0.8
Temperature (°C)
Load Current (A)
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
DS8525-01 March 2012
5
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.
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 toGND. The built-in soft-start
circuit reduces the start-up current spike and output
voltage overshoot. The external capacitor charged by an
internal 4μAconstant charging current determines the soft-
start 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
Boost Output Voltage Setting
The regulated output voltage is set by an external resistor
divider according to the following equation :
RFB1
RFB2
⎛
⎝
⎞
⎟
⎠
VOUT = VFB × 1+
, where VFB = 1.25V (typ.)
⎜
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.
according to the following equation :
5
t
≅ C ×5×10
SS
SS
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.
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.
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
Switching Frequency vs. RSW
600
current flow through a slope compensation resistor RSLP
.
500
400
300
200
100
0
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 :
V
− V ×R
IN S
(
>
)
OUT
RSLP
2×L×50μ×fSW
where RS is current sensing resistor, L is inductor value,
and fSW is boost switching frequency.
0
50
100
150
200
250
RSW (k )
Ω
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:
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,
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
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6
RT8525
0.4 −DMAX ×RSLP ×50μ
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.
RS
<
IL, PK
where IL, PK is peak inductor current, andDMAX 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 :
ROVP1
ROVP2
⎛
⎝
⎞
⎟
⎠
VOUT (OOVP) = VOOVP × 1+
,
⎜
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
secondary. The VDC regulator in the RT8525 has a fixed
output current limit to protect the IC and provide 12VDRV
voltage forN-MOSFET switch gate driver.
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
12V
R
FLT
100k
FAULT
+
-
+
+
8k
Action 1
Node A Comparator 1
1.25V
0.25V
OUVP, OTP
OOVP
+
Action 2
-
Switch 1
Switch 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,
and D is the duty cycle calculated by the following
equation :
V
− V
IN
OUT
OUT
V
D =
2
D× 1−D × V
(
)
OUT
L =
The boost converter operates inDCM 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
2×f
×I
SW OUT
where
VOUT is the maximum output voltage,
VIN is the minimum input voltage,
Copyright 2012 Richtek Technology Corporation. All rights reserved.
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7
DS8525-01 March 2012
RT8525
selected with a saturated current rating greater than the
peak current provided by the following equation :
ΔI
L
V
×I
VIN×D×T
2×L
Input Current
OUT OUT
Inductor Current
I
=
+
LPK
η × V
IN
where η is the efficiency of the power converter.
Output Current
Diode Selection
Time
Output Ripple
(1-D)T
S
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.
Voltage (ac)
Time
ΔV
OUT1
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 :
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 :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TAis
⎡
⎤
the ambient temperature, and θJA is the junction to ambient
V
1
2
1
2
1
2
⎛
⎜
⎝
⎞ ⎛
+ I
⎞
⎟
⎠
IN
Q =
×
I
IN
+
ΔI −I
−
ΔI −I
L OUT
×
L
OUT
IN
⎟ ⎜
⎠ ⎝
⎢
⎣
⎥
⎦
V
OUT
thermal resistance.
1
×
= C
× ΔV
OUT OUT1
f
SW
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 :
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 :
D×I
OUT
×f
ΔV
=
OUT1
η ×C
OUT SW
Finally, by taking ESR into consideration, the overall output
ripple voltage can be determined as the following
equation :
PD(MAX) = (125°C − 25°C) / (100°C/W) = 1.000W for
SOP-14 package
D×I
OUT
×f
ΔV
= I ×ESR+
IN
OUT
η×C
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(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.
OUT SW
Copyright 2012 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8525-01 March 2012
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8
RT8525
Layout Considerations
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Single-Layer PCB
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.
` 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.
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 4. Derating Curve of Maximum PowerDissipation
` 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
CC2.
Place the power components as close as possible. The traces
should be wide and short especially for the high-current loop.
V
IN
The compensation circuit
should be kept away from
the power loops and should
be shielded with a ground
trace to prevent any noise
PGND
V
V
IN
OUT
D1
L1
C
IN
C
coupling.
OUT
14
VDC
VIN
COMP
DRV
PGND
EN
ISW
OOVP
FB
M1
2
3
4
5
6
7
13
12
11
10
9
PGND
R
S
AGND is suggested
that connect to PGND
from the sense resistor
R
SLP
R
SS
FSW
AGND
PWMI
C
R
C
OVP2
C2
C
C1
R
for better stability.
S
R
OVP1
OUT
AGND
R
FB2
8
FAULT
R
FB1
V
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
Copyright 2012 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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DS8525-01 March 2012
9
RT8525
Outline Dimension
H
A
M
J
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
8.738
3.988
1.753
0.508
1.346
0.254
0.254
6.198
1.270
Min
Max
0.344
0.157
0.069
0.020
0.053
0.010
0.010
0.244
0.050
A
B
C
D
F
H
I
8.534
3.810
1.346
0.330
1.194
0.178
0.102
5.791
0.406
0.336
0.150
0.053
0.013
0.047
0.007
0.004
0.228
0.016
J
M
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.
DS8525-01 March 2012
www.richtek.com
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