at91sam7l128 ATMEL Corporation, at91sam7l128 Datasheet - Page 16

• Manufacturer Part Number: at91sam7l128
• Description: At91 Arm Thumb-based Microcontroller
• Manufacturer: ATMEL Corporation

5.6
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LCD Power Supply
AT91SAM7L128/64 Preliminary
Adequate input supply decoupling is mandatory for VDDIO1 in order to improve startup stability
and reduce source voltage drop. The input decoupling capacitor should be placed close to the
chip. For example, two capacitors can be used in parallel, 100 nF NPO and 4.7 µF X7R.
The AT91SAM7L128/64 embeds an on-chip LCD power supply comprising a regulated charge
pump and an adjustable voltage regulator.
The regulated charge pump output delivers 3.6V as long as its input is supplied between 1.8V
and 3.6V. The regulated charge pump only requires two external flying capacitors and one exter-
nal tank capacitor to operate.
Adequate input supply decoupling is mandatory for VDDINLCD in order to improve startup sta-
bility and reduce source voltage drop. The input decoupling capacitor should be placed close to
the chip.
Current consumption of the charge pump and LCD bias when active is 350 µA (max case).
The regulated charge pump can be used to supply the LCD voltage regulator or as a 3.6V volt-
age reference delivering up to 4 mA.
The LCD voltage regulator output voltage is software selectable from 2.4V to 3.4V with 16 lev-
els. Its input should be supplied in the range of 2.5 to 3.6V. The LCD voltage regulator can be
supplied by the regulated charge pump output or by an external supply.
When the LCD voltage regulator is not used, its output must be connected to an external source
in order to supply the PIOA and PIOB I/O lines.
Figure 5-3
Figure 5-3.
below shows the typical schematics needed:
External supply
The Charge Pump Supplies the LCD Regulator
R = 10
VDDINLCD
VDDLCD
VDD3V6
VDDIO2
Regulator
Voltage
Charge
Pump
LCD
CAPP1
CAPM1
CAPP2
CAPM2
6257AS–ATARM–28-Feb-08