MAX14720 Datasheet, PDF (15/38 Pages) Maxim Integrated Products – Extended System Battery Use Time

MAX14720/MAX14750
Power-Management Solution
When the device begins the shutdown process, reset
is driven low, all functions are disabled and outputs are
actively discharged. Then, 10ms later, the device will be in
the off state (seal mode) where all functions are disabled
except for the power button monitor.
Power Sequencing (MAX14720 Only)
The sequencing of the voltage regulators during power-
on is configurable. Each regulator can be configured to
be turned on at one of four points during the power-on
process. The four points are: t_BOOT after the power-on
event, after the RST signal is released, or at two points in
between. The two points in between are fixed proportionally
to the duration of the POR process, but the overall time of
the reset delay is configurable at 80ms, 120ms, 220ms,
and 420ms. (Note that the actual turn-on time of some
converters may be limited by the soft-starting of the output.)
Figure 2 shows the timing relationship. Additionally, the
regulators can be preselected to default off and can be
turned on with an I²C command after reset is released.
Battery Impedance Measurement
The MAX14720 contains circuitry to measure the impedance
of the power supply. To perform this measurement, SWIN
must be connected to V_CC, with no capacitor present
on the battery-side; all loads draw their power from the
power-switch output (see Typical Application Circuits).
By default, the power switch is configured with a soft-start
current limit that prevents potential high current drawn
from the battery. This soft-start lasts 60ms after the power
switch is turned on.
During battery measurement, the impedance measurement
circuitry will open the power switch and record the voltage
at the input to the switch before and after a current load is
POWER ON
RESET
TBOOT
tRST
RST
_OUT**
_Seq***
% of tRST
010
011
100
0%
25%
50%
111*
100%
*OUTPUT CONTROLLED BY STATE OF REGISTER ENABLE BITS.
**_OUT = HVOUT, BOUT, LOUT, or SWOUT
***_Seq = BoostSeq, BuckSeq, LDOSeq, OR SWSeq
Figure 2. Reset Sequence Programming (MAX14720)
applied. During the measurement, the system must rely
on the energy stored in the capacitor attached to the output
of the switch for operation. If the SWOUT voltage falls
below SWOUT UVLO threshold, the battery measurement is
immediately aborted and the power switch closes.
The parameters of the current load and the timing
of the pulse are specified in registers BatTime(0x0D)
and BatCfg(0x0E) when the measurement is requested
and the results are presented in registers BatV(0x0F),
BatOCV(0x10), and BatLCV(0x11) (see Figure 3).
I²C Interface
The devices use the two-wire I²C interface to communicate
with the host microcontroller. The configuration settings
and status information provided through this interface are
detailed in the register descriptions.
I²C Addresses
The registers of the devices are accessed through the
slave address of 010101Ax (A is configurable by OTP).
WAIT 1ms
RESET:
BCV, OCV, LCV
TAKE
MEASUREMENT
BCVTm = 0
YES
OCVTm = 0
YES
NO
WAIT BCVTm
MEASURE BCV
NO
OPEN SWITCH WAIT
OCVTm MEASURE OCV
NO
LCVTm = 0
YES
CLOSE SWITCH WAIT
1ms
*SKIPPED IF LcvDly2Skip = 1
ENABLE LOAD WAIT LCVTm
MEASURE LCV DISABLE
LOAD WAIT LCVTm*
DONE
Figure 3. Battery Impedance Measurement
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