LTC4099 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4099' PDF : 36 Pages View PDF
LTC4099
Operation
Introduction
The LTC4099 is an I2C controlled power manager and
Li‑Ion charger designed to make optimal use of the power
available from a variety of sources while minimizing power
dissipation and easing thermal budgeting constraints. The
innovative PowerPath architecture ensures that the ap-
plication is powered immediately after external voltage is
applied, even with a completely dead battery, by prioritizing
power to the application.
The LTC4099 includes a Bat-Track monolithic step-down
switching regulator for USB, wall adapters and other 5V
sources. Designed specifically for USB applications, the
switching regulator incorporates a precision average in-
put current limit for USB compatibility. Because power is
conserved, the LTC4099 allows the load current on VOUT to
exceed the current drawn by the USB port making maximum
use of the allowable USB power for battery charging. The
switching regulator and battery charger communicate to
ensure that the average input current never exceeds the
USB specifications.
For automotive and other high voltage applications, the
LTC4099 provides Bat-Track control of an external Linear
Technology step-down switching regulator to maximize bat-
tery charger efficiency and minimize heat production.
When power is available from both the USB and an aux-
iliary input, the auxiliary input is prioritized.
The LTC4099 contains both an internal 180mΩ ideal diode
as well as an ideal diode controller for use with an external
P-channel MOSFET. The ideal diodes from BAT to VOUT
guarantee that ample power is always available to VOUT even
if there is insufficient or absent power at VBUS or WALL.
The LTC4099 features an overvoltage protection circuit
which is designed to work with an external N-channel
MOSFET to prevent damage to its input caused by ac-
cidental application of high voltage.
To prevent battery drain when a device is connected to a
suspended USB port, an LDO from VBUS to VOUT provides
either a low power or high power USB suspend current
to the application.
Finally, the LTC4099 has considerable adjustability built
in so that power levels and status information can be
controlled and monitored via a simple two wire I2C port.
14
Bat-Track Input Current Limited Step-Down Switching
Regulator
The power delivered from VBUS to VOUT is controlled by a
2.25MHz constant-frequency step-down switching regu-
lator. To meet the maximum USB load specification, the
switching regulator contains a measurement and control
system which ensures that the average input current re-
mains below the level programmed at the CLPROG pin
and I2C port. VOUT drives the combination of the external
load and the battery charger.
If the combined load does not cause the switching power
supply to reach the programmed input current limit, VOUT
will track approximately 0.3V above the battery voltage.
By keeping the voltage across the battery charger at this
low level, power lost to the battery charger is minimized.
Figure 1 shows the power path components.
If the combined external load plus battery charge current
is large enough to cause the switching power supply to
reach the programmed input current limit, the battery
charger will reduce its charge current by precisely the
amount necessary to enable the external load to be satis-
fied. Even if the battery charge current is programmed to
exceed the allowable USB power, the USB specification
for average input current will not be violated; the battery
charger will reduce its current as needed. Furthermore, if
the load current at VOUT exceeds the programmed power
from VBUS, the extra load current will be drawn from the
battery via the ideal diodes even when the battery charger
is enabled.
The current out of CLPROG is a precise fraction of the
VBUS current. When a programming resistor and an av-
eraging capacitor are connected from CLPROG to GND,
the voltage on CLPROG represents the average input
current of the switching regulator. As the input current
approaches the programmed limit, CLPROG reaches
1.18V and power delivered by the switching regulator
is held constant.
The input current limit has eight possible settings rang-
ing from the USB suspend limit of 500µA up to 1.2A
for wall adapter applications. Two of these settings are
specifically intended for use in the 100mA and 500mA
USB applications.
4099fd
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