
P95020 / Preliminary Datasheet
Revision 0.7.10
59
2010 Integrated Device Technology, Inc.
current limit configuration registers. If INT_ILIM (bit7) of current limit configuration register (0xA090) is 1, the current limit
is defined by I_ILIM[2:0]. If INT_ILIM is 0, the current limit is defined by GPIO4/CHRG_ILIM pin. Low stands for 500mA
current limit while high stands for 1.5A current limit. The default setting is 100mA when VSYS is not ready at start up.
When VSYS is ready, the current limit value is obtained from the internal register setting, which can be a default setting
(power up) or dynamic setting (after the external application processor programs it).
VSYS drives both the system load and the battery charger. If the combined load does not cause the switching regulator to
exceed the programmed input current limit, VSYS will track approximately 0.3V above the battery. By keeping the voltage
across the battery charger low, efficiency is optimized because power lost to the linear battery charger is minimized.
Power available to the external load is therfore optimized.
If the combined system load at VSYS is large enough to cause the switching power supply to reach the programmed input
current limit, VSYS will drop. Depending on the configuration, the battery charger will reduce its charge current when the
VSYS drop below 3.6V to enable the external load to be satisfied.
If the voltage at VBAT is below 3.3V and the load requirement does not cause the switching regulator to exceed the
programmed input current limit, VSYS will regulate at 3.6V. If the load exceeds the available power, VSYS will drop to a
voltage between 3.6V and the battery voltage. Figure 10 shows the range of possible voltages at VSYS as function of
battery voltage.
For very low battery voltage, due to limited input power, charging current will tend to pull VSYS below the 3.6V “instant-on”
voltage. If instant-on operation under low battery conditions is a requirement then DIS_INST_ON of Charger Special
Control Register (0xA094) should be set to 0. An under voltage circuit will automatic detects that VSYS is falling below 3.6V
and disable the battery charging. If maximun charge current at low battery voltage is preferred, the instant-on function
should be disabled by setting DIS_INST_ON to 1. If the load exceed the current limit at VBUS and the system is not in the
instant-on mode, the battery charger will reduce its charge current when under voltage circuit detects VSYS is falling below
3.6V.
4.2V
3.9V
3.6V
3.3V
3.0V
2.7V
2.4V
4
.2
V
3
.9
V
3
.6
V
3
.3
V
3
.0
V
2
.7
V
2
.4
V
VBAT
VSYS
4
.5
V
Figure 13
– V
SYS Regulation Curve (Tracking VBAT )
3.7
IDEAL DIODE FROM VBAT TO VSYS
The charger has and internal ideal diode as well as a controller for an optional external ideal diode. The ideal diode
controller is always on and will respond quickly whenever VSYS drops below VBAT. If the load current increases beyond the
power allowed from the switching regulator, additional power will be pulled from the battery via the ideal diode.
Furthermore, if power to VBUS (USB or wall power) is removed, then all of the application power will be provided by the
battery via the ideal diode. The ideal diode consists of a precision amplifier that enables a large on-chip P-channel
MOSFET transistor whenever the voltage at VSYS is approximately 15mV below the voltage at VBAT. The resistance of the
internal ideal diode is approximately 180m
If this is sufficient for the application, then no external components are
necessary. However, if more current is needed, an external P-channel MOSFET transistor can be added from VBAT to