参数资料
| 型号： | LTC4101EG#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 23/30页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR BATT CHRG 24-SSOP |
| 标准包装： | 59 |
| 功能： | 充电管理 |
| 电池化学： | 智能电池 |
| 电源电压： | 6 V ~ 28 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 24-SSOP |
| 包装： | 管件 |
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LTC4101
APPLICATIONS INFORMATION
Table 10. Recommended Inductor Values
The MOSFET power dissipations at maximum output
Inductance
V IN Range (V)
≤ 7.5
≤ 9.0
≤ 12.0
≤ 15.0
1
16μH ± 20%
20μH ± 20%
24μH ± 20%
26μH ± 20%
I MAX (A)
2
8μH ± 20%
10μH ± 20%
12μH ± 20%
13μH ± 20%
3* and 4
4μH ± 20%
5μH ± 20%
6μH ± 20%
6.5μH ± 20%
current are given by:
PMAIN = V OUT /V IN (I MAX ) 2 (1 + δΔ T)R DS(ON)
+ k(V IN ) 2 (I MAX )(C RSS )(f OSC )
PSYNC = (V IN – V OUT )/V IN (I MAX ) 2 (1 + δΔ T)R DS(ON)
Where δ ΔT is the temperature dependency of R DS(ON) and
≤ 28.0 30μH ± 20% 15μH ± 20% 7.5μH ± 20%
R SENSE 0.1Ω 0.05Ω 0.025Ω
* 3 Amp uses the same R SENSE that 4 amps uses. Thus the inductance
can be the same.
Choose and inductor who’s inductance value is equal to
or greater than the value shown. Values assume:
1. –32% RSS result from –20% inductance tolerance
and a –25% inductance loss at I MAX .
2. Inductor ripple current ratio of 0.51 of I OUT across
R SENSE .
3. V OUT is at 4.2V
Charger Switching Power MOSFET
and Diode Selection
Two external power MOSFETs must be selected for use
with the charger: a P-channel MOSFET for the top (main)
switch and an N-channel MOSFET for the bottom (syn-
chronous) switch.
The peak-to-peak gate drive levels are set internally. This
voltage is typically 6V. Consequently, logic-level threshold
MOSFETs must be used. Pay close attention to the BV DSS
speci?cation for the MOSFETs as well; many of the logic
level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the “ON”
resistance R DS(ON) , total gate capacitance Q G , reverse
transfer capacitance C RSS , input voltage and maximum
output current. The charger is operating in continuous
mode so the duty cycles for the top and bottom MOSFETs
are given by:
Main Switch Duty Cycle = V OUT /V IN
Synchronous Switch Duty Cycle = (V IN – V OUT )/V IN .
k is a constant inversely related to the gate drive current.
Both MOSFETs have I 2 R losses while the PMAIN equation
includes an additional term for transition losses, which
are highest at high input voltages. For V IN < 20V the high
current ef?ciency generally improves with larger MOSFETs,
while for V IN > 20V the transition losses rapidly increase to
the point that the use of a higher R DS(ON) device with lower
C RSS actually provides higher ef?ciency. The synchronous
MOSFET losses are greatest at high input voltage or during
a short circuit when the duty cycle in this switch in nearly
100%. The term (1 + δΔ T) is generally given for a MOSFET
in the form of a normalized R DS(ON) vs temperature curve,
but δ = 0.005/°C can be used as an approximation for low
voltage MOSFETs. C RSS = Q GD / Δ V DS is usually speci?ed
in the MOSFET characteristics. The constant k = 2 can be
used to estimate the contributions of the two terms in the
main switch dissipation equation.
If the charger is to operate in low dropout mode or with
a high duty cycle less than 50%, then the bottomside
N-Channel ef?ciency generally improves with a larger
MOSFET. Using asymmetrical MOSFETs may achieve cost
savings or ef?ciency gains.
Both of the LTC4101 MOSFET drivers are optimized to
take advantage of MOSFETs Q G values of less than 22nC
and a TD-off delay speci?cation of around 60ns or less.
Larger FETs may work, but you must qualify them and
monitor LTC4101 temperature rise.
Using excessively large MOSFETs relative to the I MAX
charge current they are working with will actually reduce
ef?ciency at lighter current levels with very limited gain
at high currents. A good place to start looking for a suit-
able MOSFET in a data sheet is to look for a part with
an I D rating a little over 2 times the I MAX charge current
rating. For the LTC4101, the P-channel FET can typically
be scaled down a bit to take advantage of the lower duty
cycle limits. However make sure you never exceed the P D
rating of the device.
4101fa
23
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