LTC4054L 查看數據表（PDF） - Linear Technology

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LTC4054L

150mA Standalone Linear Li-Ion Battery Charger in ThinSOT

Linear Technology 

LTC4054L-4.2

APPLICATIO S I FOR ATIO

Stability Considerations

The constant-voltage mode feedback loop is stable with-

out an output capacitor provided a battery is connected to

the charger output. With no battery present, an output

capacitor is recommended to reduce ripple voltage. When

using high value, low ESR ceramic capacitors, it is recom-

mended to add a 1Ω resistor in series with the capacitor.

No series resistor is needed if tantalum capacitors are

used.

In constant-current mode, the PROG pin is in the feedback

loop, not the battery. The constant-current mode stability

is affected by the impedance at the PROG pin. With no

additional capacitance on the PROG pin, the charger is

stable with program resistor values as high as 20k. How-

ever, additional capacitance on this node reduces the

maximum allowed program resistor. The pole frequency

at the PROG pin should be kept above 100kHz. Therefore,

if the PROG pin is loaded with a capacitance, CPROG, the

following equation can be used to calculate the maximum

resistance value for RPROG:

RPROG

≤

2π

1

• 105 •

CPROG

Average, rather than instantaneous, charge current may

be of interest to the user. For example, if a switching power

supply operating in low current mode is connected in

parallel with the battery, the average current being pulled

out of the BAT pin is typically of more interest than the

instantaneous current pulses. In such a case, a simple RC

filter can be used on the PROG pin to measure the average

battery current as shown in Figure 2. A 10k resistor has

been added between the PROG pin and the filter capacitor

to ensure stability.

Power Dissipation

The conditions that cause the LTC4054L to reduce charge

current through thermal feedback can be approximated by

considering the power dissipated in the IC. Nearly all of

this power dissipation is generated from the internal

MOSFET—this is calculated to be approximately:

PD = (VCC – VBAT) • IBAT

where PD is the power dissipated, VCC is the input supply

voltage, VBAT is the battery voltage and IBAT is the charge

current. The approximate ambient temperature at which

the thermal feedback begins to protect the IC is:

TA = 120°C – PDθJA

TA = 120°C – (VCC – VBAT) • IBAT • θJA

PROG

LTC4054L

GND

10k

RPROG

CHARGE

CURRENT

MONITOR

CIRCUITRY

CFILTER

4054L42 F02

Figure 2. Isolating Capacitive Load on PROG Pin and Filtering

4054l42f

11

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