MP1529DR MPS [Monolithic Power Systems], MP1529DR Datasheet - Page 8

• Manufacturer Part Number: MP1529DR
• Description: Fixed Frequency Step-Up Converter LCD Backlight Plus Flash
• Manufacturer: MPS [Monolithic Power Systems]

Notes:
5) Backlight and Backlight plus Preview may use PWM for backlight brightness control. Only strings 1 & 2 will respond to high speed PWM.
6) Any combination of backlight string may be used. 1 or 2 or 1 & 2 will regulate properly. The part uses over voltage detection to determine
7) Changing from backlight plus preview to flash will have a delay equal to the soft-start timer due to the PWM filtering necessary for preview.
APPLICATION INFORMATION
Setting the LED currents
Resistors RS1, RS2 and RS3 set the backlight
LED string (LED1 and LED2) current, the flash
LED string (LED3) preview current, and the
flash
Determine each current setting resistor in kΩ by
the equations:
Where V
typically 1.216V. I
the backlight LED string current, the flash LED
string preview current, and the flash LED string
flash current in mA, respectively.
Selecting the Input Capacitor
An input capacitor is required to supply the AC
ripple current to the inductor, while limiting
noise at the input source. This capacitor must
have low ESR, so ceramic is the best choice.
MP1529 Rev. 1.0
11/23/2005
Backlight plus
String 3 will remain continuously on or off depending on the mode.
which strings are available to light. The remaining strings are then used for regulation. The part will not remain in an open loop mode if
there is at least one string of LEDs to light.
Switching the part to off mode then to flash will cancel the timer. This will take a few microseconds instead of the 10 milliseconds typically
associated with the timer being active.
Backlight
Preview
Mode
Flash
Off
LED
SET
TM
is the internal reference voltage,
MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
RS
RS
string
RS
3
2
1
LED_BL
=
=
H (PWM)
H (PWM)
=
1100
1000
950
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
EN1
I
I
L
L
I
LED
, I
LED
LED
current,
×
×
×
LED_PV
_
_
V
_
V
V
BL
PV
FL
SET
SET
SET
Table 1—Enable Operation Table
and I
EN2
respectively.
H
H
L
L
LED_FL
© 2005 MPS. All Rights Reserved.
www.MonolithicPower.com
Strings 1 & 2: LCD Backlight LEDs
Off
On (PWM)
On (PWM)
Off
are
Use an input capacitor value of 4.7µF or
greater.
physically close to the IN pin. Since it reduces
the voltage ripple seen at IN, it also reduces the
amount of EMI passed back along that line to
the other circuitry.
Selecting the Output Capacitor
A single 1µF to 4.7µF ceramic capacitor usually
provides sufficient output capacitance for most
applications. The impedance of the ceramic
capacitor
dominated by the capacitance, and so the
output voltage ripple is mostly independent of
the ESR. The output voltage ripple V
calculated as:
Where V
input voltage, I
the capacitance of the output capacitor, and f
is the 1.2MHz switching frequency.
OUT
This
(5, 6, 7)
at
V
RIPPLE
is the output voltage, V
LED
the
capacitor
is the total LED current, C2 is
=
I
V
LED
switching
O
UT
String 3: Flash LEDs
Off
Off
Preview current
Flash current
(
V
×
O
UT
C
must
2
−
×
V
f
SW
IN
frequency
)
be
IN
RIPPLE
placed
is the
SW
is
is
8