LED Boost Driver, Dual channel, PWM, 1-Wire Dimming, using the LV52207NXB

AND9425/D
LED Boost Driver, Dual channel,
PWM, 1-Wire Dimming,
using the LV52207NXB
Overview
The LV52207NXB is a high voltage boost driver for LED drive with 2 channels
adjustable constant current sources.
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Features
 Operating Voltage from 2.7V to 5.5V
 Integrated 40V MOSFET
 1-Wire 255 level digital and PWM dimming
 Supports CABC
 600kHz Switching Frequency
 37.5V Over Voltage Protection (OVP) Threshold
APPLICATION NOTE
PACKAGE PICTURE
Typical Applications
LED Display Backlight Control
WLP9J, 1.31x1.31, 0.4mm pitch
(1.31mm x 1.31mm, Amax=0.65 mm)
PIN CONNECTION
TOP VIEW
Fig1. 5x2 LED Application
1
A
B
C
© Semiconductor Components Industries, LLC, 2016
April 2016- Rev. 0
1
RT
2
3
LEDO LEDO
2
1
PWM FCAP GND
EN
VIN
SW
Publication Order Number:
AND9425/D
AND9425/D
< Overall composition >
LV52207NXB is a Boost type DC-DC convertor for
White LED drive. It integrated a MOSFET which can
tolerate 40V. The maximum LED current is set by
resistance connected to RT terminal. Case of 63.4KΩ,
it is 20mA.
We can set 256 steps of current values by using
1-wire control. (Digital mode) We can adjust dimming
for LED currents by PWM signal. (PWM mode)
Change of LED current do not synchronize the PWM
signal. It is converted to DC current by LPF of FCAP
PIN.
The switching frequency of LV52207NXB is
600kHz to improve efficiency (The switching
frequency of LV52207XA is 1200kHz)
VBAT
D1
L1
4.7uH
C1
R1
1uF
SW
10Ω
VCC
C4
1uF
SWIRE
OCP
TSD
vref
EN
1uF
OVP
UVLO
GND
0.6MHz PWM
Controler
1-wire/EN
CONTROL
LEDO1
PWM
FCAP
C2
LEDO2
PWM
dimming
D/A
IREF
RT
R2
63.4kΩ
C3
330nF
Fig.2 Block Diagram
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AND9425/D
< Explanation of the terminal >
PIN PIN
Equivalent circuit
No. Sign
Explanations
A1
RT
Resistance connect PIN for
maximum LED current setting ;
Resistance to set the maximum LED
current is connected to this terminal
between GND.
Case of 63.4KΩ, the maximum LED
current is set 20mA to LEDO1 and
LEDO2.
A2
A3
LEDO2
LEDO1
Sink Pin of the LED current ;
This PIN connect to the cathodal of
the LED and pulls a set current.
The voltage is used for the feedback
control of DC-DC converter.
B1
PWM
Input PIN of PWM control signal ;
This PIN is used for dimming of the
LED.
Continued on next page
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AND9425/D
Continued from preceding page
PIN
No.
PIN
Sign
B2
FCAP
B3
C1
GND
EN
Equivalent circuit
Explanations
Filter PIN for input PWM signals ;
A capacitor to convert PWM signal
into DC is connected to this PIN.
GND PIN
Input PIN of EN and 1-wire control
signal ;
This PIN is used for enabling and
dimming ( 1-wire control ) of the
LED.
C2
C3
VIN
SW
Power supply PIN (2.7V-5.5V)
Switching PIN ;
SW is output PIN of DC-DC
convertor.
It is used for overvoltage detection at
the time of the LED opening.
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AND9425/D
< LED Current setting and Select of control mode >
The LED current is set in the IC inside.
The maximum LED current is 20mA, when you select
63.4KΩ to RT resistor.
LED Current Setting (max sink current)
LED_full current is set by an external resistor
connected between the RT pin and ground.
I(LED_full)= 2113 x (V(RT)/R(RT_res))
V(RT) : RT_pin DC Voltage typ=0.6V
R(RT_res) : RT_pin resistor
code
0
D8
0
D7
0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
6
0
0
7
0
0
8
0
0
9
0
0
10
0
0
.
.
.
.
.
.
246
1
1
247
1
1
248
1
1
249
1
1
250
1
1
251
1
1
252
1
1
253
1
1
254
1
1
255
1
1
Default code=255
RT_res=63.4kΩ : I(LED_full)=20mA
LED Current setting Address=00 RT resistor
= 63.4KΩ
LED current = I (maximum LED current) x code /
255 = LEDO1current = LEDO2current.
Table.1 Conversion list of LEDI Setting v.s. LED
Current
D6
0
D5
0
D4
0
D3
0
D2
0
D1
0
LED Current (mA)
0 Unavailable
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0.22
0.3
0.38
0.47
0.55
0.63
0.7
0.78
0.86
0.94
.
.
.
19.3
19.38
19.46
19.54
19.61
19.69
19.77
19.84
19.93
20
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AND9425/D
Fig.3 shows the control curve by the digital mode.
Fig.4 shows the control curve by the PWM mode.
By the PWM mode, the LED current is decided
with input signal DUTY.
Fig.4 PWM Mode
Fig.3 Digital Mode
Fig.5 RT resistance value VS LED CURRENT
Fig.7 PWM frequency VS LED CURRENT
Fig.6 CABC DIMMING
PWM DIMMING + 1-wire DIMMING
PAIR=(Imax-Iaverage)/Iaverage
Iaverage=(LEDO1current+LEDO2current)/2
Fig.8 Output Current Matching
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AND9425/D
< Start/Shut Down sequences >
1. Please set PWM PIN "High", when you use only
1-wire control for dimming.
IC will start by 1-wire signal input.
2. Please set EN PIN "High", when you use only
PWM control for dimming.
IC will start by PWM signal input.
3. When you perform dimming with 1-wire and
PWM, the next condition is necessary for IC start.
During Tw0 period of 1-wire, PWM must be set
"High".
Because Tw0 must be more than 100uS, please
4.
1-wire timing
PWM timing
1-wire + PWM timing
Fig.9 SWIRE Timing Diagram
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use frequency of more than 10KHz for PWM
signal.
In the case of less than 10kHz PWM frequency,
after starting IC with PWM PIN "High", please
input PWM signal and then transmit 1-wire data.
It will shut down when EN PIN is set "Low" for
longer than Toffen(2.5ms) period or
PWM PIN is set "Low" for longer than
Toffpwm(20ms) period.
The Data register will get initialized when IC is
shut down.
AND9425/D
PWM=50%(10kHz) EN=1-WIRE START_UP VCC=3.6V
CH1(Yellow):VCC(5V/DIV)
CH2(Green):EN(5V/DIV)
CH3(Red):PWM(5V/DIV)
CH4(Blue):VOUT(5V/DIV)
Note: When starting up at 1-wire(EN)+PWM , PWM freq.>10KHz is required
Fig.10 1-wire(EN)+PWM START_UP (CABC)
Table.2 BITMAP of the LED Control
R/W
DATA
D9
D8
D7
D6
D5
D4
D3
D2
LEDI [7:0]
1
1
1
1
1
1
1
1
Upper column : Register name Lower column : Default value
W
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AND9425/D
LED OPEN/SHORT
< When both LED strings become open.>
If both LED strings are open, LEDO1 pin voltage and
LEDO2 pin voltage is about ground,
and the boost output voltage is increased When SW
LED 7s2p
pin voltage is reached the SW OVP threshold the
LV52207NXB’s switching converter stops switching.
LED current=20mA setting
VOUT SW SHORT >> OPEN
SW_OVP: DCDC LATCH OFF
CH2(GREEN):DCDCOUT(10V/DIV)
CH5(RED):SW_PIN(20V/DIV)
Fig.11 BOTH STRING OPEN
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AND9425/D
< When one LED string becomes open.>
If one LED string is open, open channel voltage is
about ground, the boost output voltage is
increased and other LEDO channel voltage is
increased. When SW pin voltage is reached
the SW OVP threshold the LV52207NXB’s switching
LED 7s2p
converter stops switching.
When other LEDO pin voltage is reached the LEDO
OVP threshold, the LV52207NXB’s switching
converter stops switching.
Open channel is latch-off.
LED current=20mA setting
LEDO2 SW: OPEN >> SHORT
LED_OVP
CH1(YELLOW):LEDO1 (1V/DIV)
CH2(GREEN):DCDCOUT(10V/DIV)
CH6(ORANGE):LEDO2 (1V/DIV)
LEDO1 LATCH OFF
LEDO1 LATCH OFF
LEDO2 ON(20mA)
Fig.12 ONE LED SHORT
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AND9425/D
< When 2 LED SHORT>
LEDO pin over-voltage protection is set at 4.5V(rise)
3.5V(fall). This IC monitors the Voltage
at LEDO1 pin and LEDO2 pin. When the voltage
LED 7s2p
exceed LEDO OVP threshold,
the switching converter stops switching.
No short channel is latch-off.
LED current=20mA setting
LEDO2 SW: OPEN >> SHORT
LED_OVP
CH1(YELLOW):LEDO1 (1V/DIV)
CH2(GREEN):DCDCOUT(10V/DIV)
CH6(ORANGE):LEDO2 (1V/DIV)
LEDO1 LATCH OFF
LEDO1 LATCH OFF
LEDO2 ON(20mA)
Fig.13 TWO LED SHORT
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AND9425/D
< Board Layout >
The traces that carry the high-frequency switching
current have to be carefully designed on
the boradin order to minimize EMI, ripple and noise in
general. The loop shown on Fig.14
corresponds to the current path when LV52207N
internal switch is closed.
The thicker lines show the switching current path. All
these traces have to be short and
wide enough to minimize parasitic inductance and
resistance. Fig.15 shows the current loop,
when LV52207N switch is open. Both loop areas
should be as small as possible.
Capacitor C1(VBAT-GND) has to be placed as close
Fig.14 Closed-switch Current Loop
as possible to the VBAT pin and GND pin.
The connection between SW pin to the inductor and
schottky diode should be kept as short
and wide as possible.
The trace between schottky diode and the output
capacitor C2 should also be as short and
wide as possible.
Capacitor C2(VOUT-GND) has to be placed as close
as possible to the GND pin.
Resistor R1(FB-GND) has to be placed as close as
possible to the RT pin.
Capacitor C3(FCAP-GND) has to be placed as close
as possible to the FCAP pin.
Fig.15 Open-switch Current Loop
< External Part Selection >
< Capacitor >
The ceramic capacitor from 1uF to 4.7uF is
recommended as input capacitor C1.
A ceramic capacitor requires attention which
capacitance value decreases to by
applying rating DC voltage.
The ceramic capacitor from 1uF to 2.2uF is
recommended as output capacitor C2.
When LED become OPEN, because the OVP voltage
is applied to each parts,
please use parts which can endure 50V.
< Schottky diode >
To get the optimum efficiency, LV52207NXB
demands a low forward voltage, high-speed
and low capacitance schottky diode . Ensure that the
diode average and peak current
rating exceeds the average output current and peak
inductor current.
In addition, the diode’s reverse breakdown voltage
must exceed the open LED protection
voltage.
< Inductor >
Three different electrical parameters need to be
considered when selecting an inductor,
the value of the inductor, the saturation current and the
DCR.
Calculation formula of the peak current
Ipeak
1
2
1
D
VIN:battery voltage, IOUT:load current, L:inductor
value, Fosc: OSC frequency,
D:duty cycle, n:converter efficiency varies with load
current.
Vout:output voltage, Vf:forward voltage of Schottky
diode.
It is important to ensure that the inductor current rating
is high enough such that it not saturate.
As the inductor size is reduced, the peak current for a
given set of conditions increases along with higher
current ripple so it is not possible to deliver maximum
output power at lower inductor values.
DCR should be small to make efficiency better.
The inductor value from 4.7uH to 10uH is
recommended.
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AND9425/D
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