User`s guide

Intel
®
StrongARM
®
SA-1110 Microprocessor Development Board User’s Guide 4-27
Hardware Considerations
4.11.2.5 LCD Power
The Sharp 3.9” LCD requires +5.0 V, +3.3 V +15 V, -14 V, and -11.7 V, all at low or very low
power levels. A MAX633 boost switching regulator is used to provide +15 V and to provide a
charge pump driver to allow the generation of a –14 V, and from that a 3.3 V Zener diode drops it to
–11.7 V. All LCD interfaces require proper sequencing of their power pins. To achieve the
sequencing, the SA-1110 Development Board powers all LCD circuits from a MIC5219 5.0 V
LDO linear regulator powered from the 5.5 V CDMA radio power rail. The battery power
conversion efficiency for this linear regulated 5 V rail powered from the boost 5.5 V output is
0.9 X 5/5.5 X 100 = 81%. The MIC5219 5.0V LDO LCD regulator regulates the 5.5 V down to
5.0 V, supports an output enable signal, and provides a very clean power rail to the LCD. The very
clean power rail to the LCD requires fewer bulk capacitors to smooth out, and results in a noise free
display. The LCD 5.0 V MIC5219 powers the MAX633 boost regulator as well as two more
MIC5219 regulators that are cascaded to provide correctly sequenced 4.0 V and 3.3 V for the LCD
and its control logic.
Most handheld devices turn on the LCD when the system is turned on. However, the SA-1110
Development Platform also supports high quality stereo audio that permits the unit to play MP3
entertainment audio like a personal stereo player. In this mode, the LCD is not needed for long
periods of time and battery charge can be substantially extended by allowing the LCD to be turned
off during audio only mode. Bit 11 in the Board Control Register, LCD On, controls the LCD
power enable.
4.11.2.6 System Power Limits
The following list defines the SA-1110 Development Board’s maximum available power:
• +3.3 V 300 mA main power–Always on to preserve DRAM contents in sleep mode
• +1.5 V to +2 V (depends on SA-1110 order number) 500 mA SA-1110 core power–Demand
switched
1
• +4.1 V to 2.7 V 1000 mA–Main Li-ion battery power to GSM radio
• +5.5 V 850 mA. CDMA radio module power–Demand switched
1
• +5.0 V 180 mA LCD power – Demand switched
1
• +15 V 25 mA LCD power – Demand switched
1
• -15 V 10 mA LCD power – Demand switched
1
• -11.7 V 1 mA LCD power – Demand switched
1
These numbers represent the maximum load limits on each rail. It is unlikely that all rails would be
fully loaded at the same time, and typical loading is much less than the maximums. The SA-1110
Development Board’s power system can sustain these maximum loads, however, the battery life
would be shortened substantially. Ideally the battery discharge current would never exceed 2C or
two times the rated battery capacity current (1000 mah to 1500 mah). The 2C limit would be
approached when using the radio module. Typical loads when not using the radio should be in the
0.1C to 0.2C range which is optimal for Li-ion batteries.
1. Controlled by the SA-1110 PWR_EN signal.