BELLING BL8588 High efficiency charge pump 4-channels led driver Datasheet

BL8588
High Efficiency 1×/1.5× Charge Pump 4-Channels LED Driver
DESCRIPTION
FEATURES
BL8588 is a low noise, high efficiency, and
constant frequency charge pump DC/DC
converter for white LED application. The
operation frequency is 1MHz.
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BL8588 works in load switch (1×) and
fractional (1.5×) modes with four independent
control outputs, each channel can provide
20mA constant current precisely from a 2.8V
to 5.5V supply. Only two external 1µF and
two 0.47µF capacitors are required to build a
compact and low-cost power supply solution.
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BL8588 uses EN pin for simple on/off control
and single wire serial pulse dimming in 16
steps. A low current shutdown feature
disconnects the load from VIN and reduces
quiescent current to less than 1µA.
APPLICATION
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TYPICAL APPLICATION CIRCUIT
BL8588
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Input range: 2.8-5.5V
±1% LED current accuracy
20mA driver capacity each channel
Auto 1×/1.5× mode switchover
PWM dimming control
Serial-pulse dimming control in linear 16
steps
Short-circuit protection
Thermal shutdown
1MHz constant switching frequency
3mm×3mm QFN package
1
Programmable Current Sinks
White LED Backlighting
Cell Phones and Smart phones
PDAs, Digital Cameras, and Camcorders
Color (RGB) Lighting
BL8588
PIN DISCRIPTIONS
Pin No.
Symbol
1
2
3
4
5
6
7
NC
NC
D4
D3
D2
D1
GND
8
VOUT
9
C2+
10
C1+
11
12
13
14
15
16
C1C2VIN
PGND
EN
NC
Description
No connection
No connection
Channel 4 sink current input
Channel 3 sink current input
Channel 2 sink current input
Channel 1 sink current input
Signal ground
Charge pump output to drive load circuit, a 1µF capacitor should be used to short
this pin to ground.
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and
C2-.
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and
C1-.
Flying capacitor 1 negative terminal.
Flying capacitor 2 negative terminal.
Power supply input, a 1µF capacitor is required to connect this pin to ground.
Power ground
Enable pin and can use this pin to program the sink current.
No connection
PIN CONFIGURATION
NC
EN
PGND
VIN
16
15
14
13
12 C2-
NC 2
11 C1-
LF
YYNZZ
NC 1
D4 3
10
D3 4
9
5
6
7
8
D2
D1
GND
VOUT
Marking :
LF: Product code
YY: LOT NO.
N: Fab code
C1+
ZZ: Date code
C2+
Top view QFN 3mm×3mm
ORDERING INFORMATION
Product NO
Ordering Number
Pin Package
BL8588
BL8588CJKTR
3*3 QFN-16
Devices per
reel
3K/reel
Temperature range & Rohs
-40~85°C & Pb free
ABSOLUTE MAXIMUM RATING
Item
VIN
Iomax
TJ
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Description
Input supply voltage
Maximum load current
Operating junction temperature range
2
Value
Unit
-0.3-6
100
-40-150
mA
V
°C
BL8588
ELECTRICAL CHARACTERISTICS
CIN=COUT=1µF, C1=C2=0.47µF, Ta=25°C, unless otherwise noted.
Symbol
VIN
V_UVLO
IQ
ISD
ILED
VTH
Description
Supply voltage range
Under voltage-lockout threshold
Quiescent operating current
Shutdown current
Sink current accuracy
1.5× mode to 1× mode
transition threshold
ROUT
Open loop out resistance
VEN
Enable voltage
TEN_PULSE
VDROPOUT
The positive and negative pulse
width of EN pin
D pin Dropout voltage
ISHORT
FOSC
TSD
Output short current
Oscillator frequency
Thermal shutdown temperature
T_H
Condition
1× mode/No load current
1.5× mode/No load current
EN=0
ISET=20mA
Min
2.8
2.5
Typical
0.3
Max
5.5
2.8
0.5
6
1
-10
+10
3.7
1x mode, (Vin-Vout)/Iout
1.5x mode, (1.5VinVout)/Iout
Logic high voltage
Logic low voltage
Dimming control
1.2
0.4
Thermal shutdown hysteretic
20
120
0.7
100
1
150
30
µA
%
Ω
5
100% LED current setting
(Note1)
Short output to ground
mA
V
2.2
4
Unit
V
V
V
µS
mV
1.3
mA
MHZ
°C
°C
Note1: Dropout voltage is defined as the D pin to GND voltage at which current into D pin drops 10% from the
value at VD=0.2V.
BLOCK DIAGRAM
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3
BL8588
TYPICAL CHARACTERISTICS
LED Curent VS Dropout Voltage
LED Current VS Pulse Number
25
20
LED Current(mA)
LED Current(mA)
25
15
10
5
0
20
15
10
5
0
0
50
100
150
200
250
0
4
8
Dropout Voltage(mV)
14
26
13
LED Current(mA)
LED Current(mA)
28
24
22
20
D1
18
D2
16
D3
14
D4
3.1
3.5 3.9 4.3 4.7
Input Voltage(V)
5.1
Quiescent Current(mA)
4
3
2
1
0
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10
D1
D2
D3
D4
9
8
3.1
3.5
3.9
4.3
4.7
Input Voltage(V)
5
1.5X Mode
11
2.7
5.5
6
3.5
4.5
Input Voltage(V)
12
7
Quiescent Current VS Input Voltage
2.5
16
LED Current Matching VS Input Voltage
(10mA/LED)
LED Current Matching VS Input Voltage
(20mA/LED)
2.7
12
Pulse Number
5.5
1X Mode
4
5.1
5.5
BL8588
OPERATION WAVEFORMS
LED current
LED current
EN
EN
Fig. 2 Shutdown from EN pin
Fig. 1 Startup from EN pin
Output voltage ripple
Input current
Input voltage ripple
LED current
Output voltage ripple
Input voltage ripple
Fig. 4 Operating at 1x mode with 100% brightness
Fig. 3 Operating at 1.5x mode with 100% brightness
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BL8588
DETAIL DESCRIPTION
Startup sequence
The BL8588 starts to work only when
powered on and the EN pin became
after a delay, the delay time is at least
EN pin is not allowed to connect to
directly or keep it floating.
current can be programmed up to 16 levels
depends on the number of rise edges of the
input waveform. A high level input (“1”) with
pulse width wider than 20uS is regarded as a
signal to stop the build-in counter. The time
between two wide high levels (more than
20uS) is a counting period. When some rise
edges occur between two high level pulses of
20us, the equation as shown below can
calculate the active pulse number, called
Code_No.
VIN
high
4us.
VIN
The BL8588 starts with 1X mode, the output
follows closely to the supply voltage. If the
average voltage of pin D1 to D4 falls below
0.25V the IC switches to 1.5X mode, and it
can automatically switch back to 1X mode
when the input voltage is higher than 3.7V.
Code _ No = Mod ( N ,16) ,
In the equation, N is the number of rise edges
of the input waveform and mod function
returns the remainder of N divided by 16. For
example, if N=0, 16, or other integral multiple
of 16, the mod function returns a value of 0, if
N=1, 17 or other integral multiple of 16 plus 1,
the mod function returns a value of 1, and so
on.
PWM dimming control
If the frequency of the PWM signal to the EN
pin is less than 5KHz, the average LED
current is proportional to the duty cycle of the
PWM signal, and the EN works as a simple
on/off control. A high level turns on and a low
shuts down the LEDs. There is a delay time
between the input PWM signal and the output
LED current waveform, as shown in Fig.5, the
TD is about 20uS.
The relationship between LEDs’ brightness
and the Code_No is listed as the following
table.
Code No
0
1
2
3
4
5
6
7
ON duty
EN
Td=20uS
Td=20uS
20mA
I_LED
Fig. 5 PWM Dimming Control
The LEDs’ brightness can also be controlled
by the pulses applied to the EN pin, Refer to
the Fig. 6. Inside the device there is a 4-bit
counter connecting to the EN pin. The LED
Code_No=1
Code_No=4
EN
20uS
20uS
Iset/20mA=15/15
Iset/20mA=12/15
Fig. 6 Linear current Dimming Control
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Code No
8
9
10
11
12
13
14
15
ISET/20mA
8/15
7/15
6/15
5/15
4/15
3/15
2/15
1/15
The frequency of the input pulse should be
lower than 100KHz, and the width of the high
level and low level larger than 4uS to prevent
false trigger.
EN dimming control
I_LE
D
ISET/20mA
0
1
14/15
13/15
12/15
11/15
10/15
9/15
6
BL8588
Short Circuit Protection
lower supply voltage of 0.3V than a LED with
VF of 3.5V. For the BL8588, the LED with
dropout lower than 3.4V is adequate.
If the voltage difference between Vout pin
and any of a D pin exceeds 1V, for example,
a LED is shorted in the circuit, the
corresponding channel will be shutdown
internally by the IC.
Connect all unused
LEDs to VOUT to avoid the accuracy
reduction of the threshold of switching to 1.5X,
and it also avoids wasting battery current.
External Component
If the Vout is shorted to ground, the BL8588
will stop operating and keep a constant
source current of about 100mA until the short
circuit is removed.
The driver requires two external 1µF ceramic
capacitors for decoupling input, output, and
for the charge pump. Both capacitors type of
X5R and X7R are recommended for the LED
driver application. In charge pump modes, the
input current ripple is kept minimal. An input
bypass capacitor of 1µF is sufficient. In 1X
mode, the device operates linearly and does
not introduce switching noise to the supply.
Thermal Protection
Layout Consideration
When the device temperature exceeds 150°C
the driver enters a thermal protection
shutdown mode. The IC resumes normal
operation once the temperature drops by
about 30°C to 120°C.
Due to its high switching frequency and high
transient current, careful consideration of
PCB layout is necessary. The input capacitor
(CIN) and the device, as well as the ground of
CIN and COUT should be placed as close as
possible. To achieve best performance, it is
recommended to minimize the distance
between components. Maximum trace width
is recommended for connection. Make sure
each device connects to immediate ground
plane. The use of multiple via improves the
package heat dissipation.
LED selection
LEDs with lower VF are recommended. from
the efficiency perspective. It keeps the driver
in the 1X mode longer hence helps improve
the efficiency and extends battery life. For
example, a white LED with a VF of 3.2V can
keep the device working in the 1X mode for
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BL8588
PACKAGE INFORMATION
Package
QFN3X3-16
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Devices per reel
8
3000
Unit
mm
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