Datasheet

ADP8860
Rev. 0 | Page 14 of 52
07967-012
NOTES
1.
V
DMAX
IS THE CALCULATED GAIN DOWN TRANSITION POINT.
WAIT
100µs (TYP)
MIN (V
D1:D7
) < V
HR(UP)
0
0
1
1
1
1
0
0
STATUP:
CHARGE
V
IN
TO V
OUT
EXIT STBY
VOUT > V
OUT(START)
1
WAIT
100µs (TYP)
WAIT
100µs (TYP)
MIN (V
D1:D7
) < V
HR(UP)
MIN (V
D1:D7
) > V
DMAX
MIN (V
D1:D7
) < V
DMAX
G = 2
G = 3/2
EXIT
STARTUP
G = 1
STBY
0
Figure 27. State Diagram for Automatic Gain Selection
Soft Start Feature
At startup (either from UVLO activation or fault/standby
recovery), the output is first charged by I
SS
(3.75 mA typical)
until it reaches about 92% of V
IN
. This soft start feature reduces
the inrush current that is otherwise present when the output
capacitance is initially charged to V
IN
. When this point is
reached, the controller enters 1× mode. If the output voltage is
not sufficient, then the automatic gain selection determines the
optimal point as defined in the Automatic Gain Selection section.
OPERATING MODES
There are four different operating modes: active, standby,
shutdown, and reset.
Active Mode
In active mode, all circuits are powered up and in a fully
operational state. This mode is entered when nSTBY (in
Register MDCR) is set to 1.
Standby Mode
Standby mode disables all circuitry except for the I
2
C receivers.
Current consumption is reduced to less than 1 A. This mode is
entered when nSTBY is set to 0 or when the nRST pin is held
low for more than 100 s (maximum). When standby is exited,
a soft start sequence is performed.
Shutdown Mode
Shutdown mode disables all circuitry, including the I
2
C receivers.
Shutdown occurs when V
IN
is below the undervoltage thresholds.
When V
IN
rises above V
IN(START)
(2.05 V typical), all registers are
reset and the part is placed into standby mode.
Reset Mode
In reset mode, all registers are set to their default values and the
part is placed into standby. There are two ways to reset the part:
power-on reset (POR) and the nRST pin. POR is activated any-
time that the part exits shutdown mode. After a POR sequence
is complete, the part automatically enters standby mode.
After startup, the part can be reset by pulling the nRST pin low.
As long as the nRST pin is low, the part is held in a standby state
but no I
2
C commands are acknowledged (all registers are kept
at their default values). After releasing the nRST pin, all registers
remain at their default values, and the part remains in standby;
however, the part does accept I
2
C commands.
The nRST pin has a 50 s (typical) noise filter to prevent inad-
vertent activation of the reset function. The nRST pin must be
held low for this entire time to activate reset.
The operating modes function according to the timing diagram
in Figure 28.