MP1015
Full System
Precision CCFL Driver
Monolithic Power Systems
Application Information (Continued)
Pin 15 (Cref):
Cref is the bypass cap for the internal 5.0V supply.
This capacitor must be placed as close as possible
to the pin. A maximum of 100 mils is recommended
between the cap and the IC. The value of the cap
is typically 0.47µF
Pin 14, Pin 7 & Pin 9 (Batt & PGnd): CbaR/L, Cba
These caps are used as the bypass caps for the
battery voltage supply line. These capacitors will
absorb most of the input switching current of the
inverter and will require adequate ripple rating. The
typical current rating for Cba is > 500mArms.
Typically CbaR and CbaL are 1µF and Cba is equal
to 2 caps of 2.2µF.
Pin 13 & Pin 8 (OutL & OutR): Cp1, Rdamp,
Rbleed
The primary transformer current flows through this
capacitor. Its value is typically 1µF and its voltage
rating is sufficient for a 5V bias. The capacitor
should be ceramic and have a ripple current rating
greater than the primary current (typically 0.8Arms).
It is more optimal to use two parallel 0.47µF
ceramic caps for minimal ESR losses.
Rdamp and Rbleed are used to ensure that the
bridge outputs are at 0V prior to startup. Typically
Rbleed = 4.3KΩ and Rdamp = 1KΩ.
Pin 11 and Pin 10 (BtL and BtR): Cbtl and Cbtr
These are the reservoir caps for the upper
switches’ gate drive. They should be 10nF and
made of X7R ceramic material and have a voltage
rating for 6.6V
biasing.
Pin 6 (Drv): Cdrv
This bypasses the 6.2V gate supply for the lower
switches. The value should be 100nF ceramic Y5V
or X7R material.
Pin 5: (En)
This pin will enable and disable the chip. Do not
float this pin.
Pin 4 (DBrt) : Rdbr, Cdbr
This pin is used for burst brightness control. The
DC voltage on this pin will control the burst
percentage on the output. The signal is filtered for
optimal
operation.
The
active
range
is
approximately 0.1V to 1.8V. The value of Rdbr and
Cdbr is not critical.
Pin 3 (Bosc): Cbosc, Rbosc
The Cbosc and Rbosc will set the burst repetition
rate and the minimum Ton. Set Tmin to achieve the
minimum required system brightness. Ensure that
Tmin is long enough that the lamp does not
extinguish. These values are determined by the
following steps:
1) Select a Minimum Duty Cycle (DMIN). This is the
ratio TFALL / (TFALL + TRISE) for the burst oscillator.
For example: 10%
2) Determine Rbosc by the formula:
1.68 * [(1 / DMIN) – 1] + 4
Rbosc =
0.42
350 * 10
-6
3) Select a burst frequency and find TTOTAL where
TTOTAL = 1/burst frequency. Then determine Cbosc
by the formula:
(1-DMIN)
0.42 * Rbosc *
fbosc
Cbosc =
Where:
fbosc= burst frequency rate in Hz
Tmin= Minimum burst time in sec
MP1015 Rev 2.7_03/25/03
www.monolithicpower.com
6
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