AT1731A
Preliminary Product Information
DC-DC Power IC for TFT Panel
rising rate of output voltage.
Short-Circuit Protection
If feedback voltage of the main regulator falls below 0.8V, positive charge-pump falls below
1.1V and negative charge-pump falls below 130mV , the built-in constant current will charge
external capacitor CSCP . If VSCP reaches 0.8V ,the ready pin goes high impedance and all
outputs shut down.; however , the reference remains active. When short- circuit problem is to
eliminate, toggle shutdown or cycle the input voltage to clear the fault latch .
Voltage Reference
The voltage at REF is nominally 1.23V. The reference can source up to 50uA with good
regulation. Connect a 0.22uF bypass capacitor between REF and GND.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the AT1731A. When the
junction temperature exceeds Tj=160 ℃, a thermal sensor activates the thermal protection,
which shuts down the IC, allowing the IC to cool. Once the device cools down by 15 ℃, IC
will automatically recover normal operation. For continuous operation , do not exceed the
absolute maximum junction-temperature rating of Tj=150 ℃.
Power dissipation consideration
The AT1731A maximum power dissipation depends on the thermal resistance of the IC
package and circuit board, the temperature difference between the die junction and ambient
air, and the rate of any airflow. The power dissipation in the device depends on the operating
conditions of each regulator.
The step-up converter dissipates power across the internal N-MOS as the controller ramps up
the inductor current. In continuous condition, the power dissipated internally can be
approximated by :
IMAIN ×V
Vin × D
12 fOSC × L
1
PMAIN−boost = [(
MAIN )2 +
(
)2 ]× RDS (ON ) × D
Vin
where
IMAIN : It includes the primary load current and the input supply current for the
charge-pumps.
The charge-pumps provide regulated output voltages by dissipating power in the low-side
N-MOS, so they could be modeled as linear regulators followed by unregulated
charge-pumps. Therefore, their power dissipation is similar to a linear regulator :
PNEG = INEG ×[(VDDN − 2×VDIODE )× N −VNEG−OUT
PPOS = IPOS ×[(VDDP − 2×VDIODE )× N −VPOS−OUT
]
]
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Tel: 886-3-563-0878
2/8/2006 REV:1.1
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15
AIMTRON [ AIMTRON TECHNOLOGY ]
