Nokia 9000i Service Manual page 153

After Sales
Technical Documentation
Table 25. Electrical characteristics (continued)
Parameter Mini-
mum
VCC5 4.825
3.04
PWRGOOD
140
VBACK 2.5
Operating tem- –25
perature range
Functional Description
VSYS regulator
System voltage regulator is current–mode pulse width modulation (PWM)
dc–dc step–down converter. It has internal switch transistor and current
sense resistor for current–mode control. Oscillator makes the switch
transistor to turn on at fixed frequency. Switch transistor on time is
determined by load taken at output. Current mode feedback makes
transient response fast and provides cycle by cycle current limiting. This
means that outer loop determines threshold voltage for current sense
amplifier to reach to turn switch transistor off. Inner current feedback loop
makes response to load current changes fast.
Outer feedback loop takes output voltage information and compares it to
reference and drives the error towards zero in order to keep regulation.
This kind of control keeps good regulation at output in rapidly changing
load conditions. Tradeoff is high operation current in very light loads
because oscillator is running all the time.
VSYS regulator operates at discontinuous conduction mode (DCM) at light
loads. This means that current through inductor decreases to zero before
new switch transistor turn–on pulse comes and current through inductor
starts to increase. At heavy loads inductor current does not go to zero
and operation is in continuous conduction mode (CCM).
Original, 08/96
Typi- Max- Units
cal mum
5.0 5.175 V
120 225 mV
30 mA
0.4 1.2 mA
3.08 3.11 V
240 560 ms
30 ppm/C reset threshold temperature
3.0 3.2 V
µA
7
130 mAh
+85 C
RAE/RAK–1N
PDA Hardware
Notes/conditions
tolerance over temperature and
load range
dropout voltage at I=50mA
regulator I =50mA
max
peak current 100mA
ground pin current (supply current)
reset threshold at room temperature
power–on reset pulse width
coefficient
nominal load when used
capacity, charging not possible
some circuits tolerate
wider temperature range
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