参数资料
型号: LTC4098EUDC#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: BATTERY CHARGE CONTROLLER, 2650 kHz SWITCHING FREQ-MAX, PQCC20
封装: 4 X 3 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, QFN-20
文件页数: 7/32页
文件大小: 443K
代理商: LTC4098EUDC#PBF
LTC4098/LTC4098-1
15
40981fc
For very low battery voltages, the battery charger acts like
a load and, due to limited input power, its current will tend
to pull VOUT below the 3.6V instant-on voltage. To prevent
VOUT from falling below this level, an undervoltage circuit
automatically detects that VOUT is falling and reduces the
battery charge current as needed. This reduction ensures
that load current and voltage are always prioritized while
allowing as much battery charge current as possible. Refer
to Overprogramming the Battery Charger in the Applica-
tions Information section.
The voltage regulation loop compensation is controlled by
the capacitance on VOUT. An MLCC capacitor of 10μF is
required for loop stability. Additional capacitance beyond
this value will improve transient response.
An internal undervoltage lockout circuit monitors VBUS and
keeps the switching regulator off until VBUS rises above
the rising UVLO threshold (4.3V). If VBUS falls below the
falling UVLO threshold (4V), system power at VOUT will
be drawn from the battery via the ideal diodes. The volt-
age at VBUS must also be higher than the voltage at BAT
by approximately 170mV for the switching regulator to
operate.
Bat-Track High Voltage External Switching Regulator
Control
The WALL, ACPR and VC pins can be used in conjunction
with an external high voltage step-down switching regulator
such as the LT3653 or LT3480 to minimize heat production
when operating from higher voltage sources, as shown in
Figures 3 and 4. Bat-Track control circuitry regulates the
external switching regulator’s output voltage to the larger
of BAT + 300mV or 3.6V. This maximizes battery charger
efficiency while still allowing instant-on operation when
the battery is deeply discharged.
When using the LT3480, the feedback network should be set
to generate an output voltage between 4.5V and 5.5V. When
high voltage is applied to the external regulator, WALL will
rise toward this programmed output voltage. When WALL
exceeds approximately 4.3V, ACPR is brought low and the
Bat-Track control of the LTC4098/LTC4098-1 overdrives
the local VC control of the external high voltage step-down
switching regulator. Therefore, once the Bat-Track control
is enabled, the output voltage is set independent of the
switching regulator feedback network.
Bat-Track control provides a significant efficiency advantage
over the simple use of a 5V switching regulator output to
drive the battery charger. With a 5V output driving VOUT,
battery charger efficiency is approximately:
ηTOTAL BUCK
VBAT
5V
where
ηBUCK is the efficiency of the high voltage switching
regulator and 5V is the output voltage of the switching
regulator. With a typical switching regulator efficiency of
87% and a typical battery voltage of 3.8V, the total battery
charger efficiency is approximately 66%. Assuming a 1A
charge current, nearly 2W of power is dissipated just to
charge the battery!
OPERATION
ACPR
40981 F03
LTC4098/
LTC4098-1
VOUT
ISENSE
WALL
VC
LT3653
VC
HVOK
SYSTEM
LOAD
SW
ACPR
40981 F04
LTC4098/
LTC4098-1
VOUT
WALL
VC
LT3480
VC
SYSTEM
LOAD
SW
FB
Figure 3. LT3653 Typical Interface
Figure 4. LT3480 Typical Interface
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