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PDF MP3388 Data sheet ( Hoja de datos )
| Número de pieza | MP3388 | |
| Descripción | 8-String White LED Driver | |
| Fabricantes | MPS | |
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The Future of Analog IC Technology
MP3388
50V, 8-String White LED Driver
DESCRIPTION
The MP3388 is a step-up converter with
8-channel current sources designed for driving
the white LED arrays for large size LCD panel
backlighting applications.
The MP3388 uses current mode, fixed frequency
architecture. The switching frequency can be
selected at 1.25MHz or 625kHz. It generates an
output voltage up to 50V from a 4.5V to 25V input
supply. The MP3388 independently regulates the
current in each LED string to the user programmed
value set by an external current setting resistor.
The MP3388 applies 8 internal current sources in
each LED string terminal to achieve a current
balance of 3% regulation accuracy between
strings. Its low 600mV regulation voltage on LED
current sources reduces power loss and improves
efficiency.
The MP3388 features external PWM dimming or
DC input PWM dimming, which allows the flexible
control of the backlighting luminance. The dimming
PWM signal can be generated internally, and the
dimming frequency is programmed by an external
setting capacitor.
FEATURES
• High Efficiency and Small Size
• 4.5V to 25V Input Voltage Range
• 50V Maximum Step-up Voltage
• Balanced Driver for 8 Strings of WLED
• 3% Current Matching Accuracy Between
Strings
• Selectable Switching Frequency: 1.25MHz or
625kHz
• PWM or DC Input Burst PWM Dimming
• Programmable Over-voltage Protection
• Under Voltage Lockout
• Open and Short LED protection
• Thermal Shutdown
• Small QFN24 (4x4mm) and 28 pin SOIC
packages
• Halogens Free
APPLICATIONS
• Notebook PC
• Small LCD TV
• Handy Terminals Display
• Automotive System and Tablet Computer
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Quality Assurance.
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
VIN
4.5V~25V
C1
M1
L1
D1
C2
R1
Enable
PWM
DIMMING
C3
24
VCC
1 EN
23
VIN
C4
22 21 20
COMP VFAULT SW1
19
SW2
PGND1 18
NC 2 OSC
3 FSET
4 PWMO
C5 C6
5 GND
MP3388
PGND2 17
OVP 16
LED1 15
LED2 14
6 PWMI
LED3 13
LED8
7
LED7
8
LED6
9
LED5
10
ISET
11
LED4
12
RSET
R2
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
1
1 page  
MP3388- 50V, 8-STRING WHITE LED DRIVERS
PIN FUNCTIONS
QFN24 SOIC28
15
26
Name Description
EN Enable Control Input. Do not let this pin floating.
OSC
Switching Frequency Selection Input. When float this pin or connect this pin to
VCC, the step-up converter switching frequency is 1.25MHz. When connect this
pin to GND, the step-up converter switching frequency is 625kHz.
3
7
FSET
Dimming PWM Frequency Setting. Connect a capacitor between FSET and GND
to set the DPWM frequency by the equation: fDPWM=3.5uF/CFSET.
PWM Filter Output. To use external PWM dimming mode, connect a capacitor
between PWMO and GND to form a low-pass filter with an internal 400kΩ resistor.
It filters the external PWM logic signal on PWMI pin into a DC signal whose level is
4
8
PWMO
inversely proportional to the duty-cycle of the input PWM signal. Then the DC
signal is converted to a DPWM dimming signal with the same duty-cycle as the
external PWM signal. To use DC input PWM dimming mode, directly apply a DC
voltage from 0.2V to 1.2V on PWMO pin for dimming PWM duty cycle control. The
DC input PWM dimming polarity is negative.
5 9 GND Analog Ground.
PWM Signal Input. To use the external PWM dimming mode, apply a PWM signal
on this pin for brightness control. This signal is filtered and its duty cycle is
6 10 PWMI converted into a DC signal to calculate the DPWM duty cycle. And the DPWM duty
cycle equals to the input PWM duty cycle. To use DC input PWM dimming mode,
float this pin.
LED String 8 Current Input. This pin is the open-drain output of an internal
7 11 LED8 dimming control switch. Connect the LED String 8 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 7 Current Input. This pin is the open-drain output of an internal
8 12 LED7 dimming control switch. Connect the LED String 7 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 6 Current Input. This pin is the open-drain output of an internal
9 13 LED6 dimming control switch. Connect the LED String 6 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 5 Current Input. This pin is the open-drain output of an internal
10 14 LED5 dimming control switch. Connect the LED String 8 cathode to this pin. If this string
is not used, connect Vout to this pin.
11
16
ISET
LED Current Setting. Tie a current setting resistor from this pin to ground to
program the current in each LED string. ILED = 1000 x 1.22V /( RSET+1kΩ)
LED String 4 Current Input. This pin is the open-drain output of an internal
12 18 LED4 dimming control switch. Connect the LED String 4 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 3 Current Input. This pin is the open-drain output of an internal
13 19 LED3 dimming control switch. Connect the LED String 3 cathode to this pin. If this string
is not used, connect Vout to this pin.
LED String 2 Current Input. This pin is the open-drain output of an internal
14 20 LED2 dimming control switch. Connect the LED String 2 cathode to this pin. If this string
is not used, connect Vout to this pin.
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
5
5 Page 
MP3388- 50V, 8-STRING WHITE LED DRIVERS
APPLICATION INFORMATION
Selecting the Switching Frequency
The switching frequency of the step-up converter
is alternative for 1.25MHz or 625kHz. A bi-level
Switching Frequency Selection (OSC) input sets
the internal oscillator frequency for the step-up
converter. Tie OSC pin to GND corresponds to
the frequency 625kHz and tie OSC pin to VCC or
floating corresponds to 1.25MHz.
Setting the LED Current
The LED string currents are identical and set
through the current setting resistor on the ISET
pin.
ILED = 1000 x 1.22V / (RSET+1kΩ)
For RSET=60.4kΩ, the LED current is set to
19.9mA. The ISET pin can not be open.
Setting the Over Voltage Protection
The open string protection is achieved through
the over voltage protection (OVP). In some cases,
an LED string failure results in the feedback
voltage always zero. The part then keeps
boosting the output voltage higher and higher. If
the output voltage reaches the programmed OVP
threshold, the protection will be triggered.
To make sure the chip functions properly, the
OVP setting resistor divider must be set with a
proper value. The recommended OVP point is
about 1.3 times higher than the output voltage for
normal operation.
VOVP=1.23V x (R1+R2)/R2
Selecting Dimming Control Mode
The MP3388 provides 4 different dimming
methods
1. PWM dimming mode with internal triangle
waveform generator
Apply a 100Hz to 50kHz square waveform to the
PWMI pin. The internal 400kΩ and external
capacitor on PWMO pin filters the dimming signal
to a DC voltage(0.2V~1.2V).Then the DC voltage
is modulated to an internal PWM dimming signal
whose frequency is set via the capacitor on FSET
pin according to the equation:
fDPWM = 3.5uF / CFSET
The minimum recommended amplitude of the
PWM signal is 2.1V (See Figure 3)
PWM Dimming
100Hz~50kHz
FSET
C1
MP3388
PWMI
PWMO
C2
Figure 3—PWM Dimming
with Internal Triangle Waveform Generator
2. Direct PWM dimming with positive logic
An external PWM dimming signal is directly
employed to achieve PWM dimming control.
Connect a 100kΩ resistor from FSET pin to GND
and apply the 100Hz to 2kHz PWM dimming
signal to PWMI pin. The minimum recommended
amplitude of the PWM signal is 1.5V (See Figure
4).
PWM Dimming
100Hz~2kHz
C1
R1
100 kO
VCC
FSET
MP3388
PWMI
PWMO
Figure 4—Direct PWM Dimming
with Positive Logic
3. Direct PWM dimming with negative logic
It is similar to method 2. Apply a 100Hz to 2 kHz
external square waveform to the PWMO pin for
negative logic PWM dimming. The minimum
recommended amplitude of the PWM signal is
1.5V (See Figure 5),
C1
R1
100 kO
VCC
FSET
MP3388
PWM Dimming
100Hz~2kHz
PWMI
PWMO
Figure 5— Direct PWM Dimming
with Negative Logic
MP3388 Rev. 1.0
12/16/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MP3388.PDF ] | |
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