LTC3576 Datasheet, PDF (30/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go + Triple Step-Down DC/DCs

LTC3576/LTC3576-1
OPERATION
The third data byte at sub-address 2 controls the operating
modes of each switching regulator as well as the input
current limit settings. Each switching regulator can be
independently set to one of three operating modes listed
in Table 5.
The input current limit settings are decoded according
to Table 6. This table indicates the maximum current
that will be drawn from the V_BUS pin in the event that the
load at V_OUT (battery charger plus system load) exceeds
the power available. Any additional power will be drawn
from the battery. The start-up state for the input current
limit setting is 00 representing the low power 100mA
USB setting.
The fourth and final byte of input data at sub-address 3
provides bits for disabling the battery charger and enabling
the high power suspend mode current limit of 2.5mA.
Table 5. General Purpose Switching Regulator Modes
C7 (SDA)* C6 (SCL)* Switching Regulator 1 Mode
C5 (SDA)* C4 (SCL)* Switching Regulator 2 Mode
C3 (SDA)* C2 (SCL)* Switching Regulator 3 Mode
0
X
Pulse Skip Mode
1
0
LDO Mode
1
1
Burst Mode Operation
*SDA and SCL take on this context only when DV_CC = 0V.
Table 6. USB Current Limit Settings
C1
C0
D6 (I_LIM1)* (I_LIM0)* USB SETTING
X
0
0 1x Mode (USB 100mA Limit)
X
0
1 10x Mode (Wall 1A Limit)
0
1
0 Low Power Suspend (USB 500μA Limit)
1
1
0 High Power Suspend (USB 2.5mA Limit)
X
1
1 5x Mode (USB 500mA Limit)
*I_LIM1 and I_LIM0 can only be used to enable the low power suspend mode
and are logically ORed with C1 and C0, respectively.
Disabling the I²C Port
The I²C serial port can be disabled by grounding the DV_CC
pin. In this mode, the LTC3576/LTC3576-1 are controlled
through the individual logic input pins EN1, EN2, EN3,
ENOTG, I_LIM0, I_LIM1, SDA and SCL. Some functionality is
not available in this mode such as the programmability of
switching regulators 1, 2 and 3’s output voltage, the battery
charger disable feature and the high power suspend mode.
In this mode, the programmable switching regulators have
a fixed servo voltage of 0.8V. Because the SDA and SCL
pins have no other context when DV_CC is grounded, these
pins are re-mapped to control the switching regulator
mode bits C2 to C7. SCL maps to C2, C4 and C6 while
SDA maps to C3, C5 and C7.
RST3 Pin
The RST3 pin is an open-drain output used to indicate that
switching regulator 3 has been enabled and has reached
its final voltage. RST3 remains low impedance until regula-
tor 3 reaches 92% of its regulation value.
A 230ms delay is included to allow a system microcontroller
ample time to reset itself. RST3 may be used as a power-
on reset to the microprocessor powered by regulator 3
or may be used to enable regulators 1 and/or 2 for supply
sequencing. RST3 is an open-drain output and requires
a pull-up resistor to the output voltage of regulator 3 or
another appropriate power source.
Shutdown Mode
The bidirectional USB switching regulator in step-down
mode is enabled whenever V_BUS is above V_UVLO and the
LTC3576/LTC3576-1are not in one of the two USB suspend
modes (500μA or 2.5mA). When power is available from
both the USB and auxiliary inputs, the auxiliary input is given
priority and the USB switching regulator is disabled.
The ideal diode(s) are enabled at all times and cannot be
disabled.
3576f
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