User`s guide

Intel
®
StrongARM
®
SA-1110 Microprocessor Development Board User’s Guide 4-21
Hardware Considerations
cells result in a 8.2 V to 5.4 V terminal voltage discharge curve, while a single cell Li-ion batteries
produce 4.1 V to 2.7 V through out its discharge cycle with a 3.6 V nominal voltage. The discharge
curves of Li-ion batteries are very flat when compared to lead acid or alkaline types. Li-ion
batteries do not exhibit the memory effects associated with NiCd batteries or the high self
discharge rates associated with NiMH batteries. In addition, Li-ion batteries have the highest
energy density (watt hours per CC) of any available, affordable battery technology.
Figure 5-1 shows the effect of higher discharge rates on a Li-ion cell. This voltage sag effect under
heavy loads is due to the internal resistance of the Li-ion cell which is less then 0.2 ohms typically.
Discharge loads that are less then 20% (0.2C) of the battery capacity result in the most power
efficient use of this battery type.
4.10.2.1 1.5V Core Power
The single Li-ion cell 1.5 V core power regulator solution is very simple and efficient. A
MAX1692 buck regulator is fed from the 4.1 V – 2.7 V single cell Li-ion battery. This regulator,
which is described in detail in Section 4.11.1, can achieve greater than 90% efficiency and is turned
off during sleep mode by the SA-1110 SA_PWR_EN signal. The MAX1692 buck regulator is a
high frequency type regulator. Powering the 1.5 V switching regulator from two Li-ion cells (8.2 V
to 5.4 V) results in less than 85% power conversion efficiency. Using a single Li-ion design instead
of two results in a greater than 90% conversion efficiency for the 1.5 V rail.
Figure 4-1. Li-ion Discharge Curves
A7267-01
Chrg
on
off
off
track
5.5v Radio power @900ma
or 3.5V during sleep
LCD
5V
Main
3.3V
Vcore
1.55V
LCD en
SA PWR EN
Batt Lockout
PWR IN
3.3V
LDO
5V
LDO
3.2V
LDO
Super
cap
3.6V
batt
SMPS
1.55V
SMPS
4.5
4.0
3.5
3.0
2.5
2.0
0 500
2C
0.2C
1000 1500
1C
Voltage / V
Capacity / mAh
Discharge Rate Characteristics
1C discharge (4.1V cccv)
20˚C