参数资料
型号: MAX8730ETI+T
厂商: Maxim Integrated Products
文件页数: 24/29页
文件大小: 0K
描述: IC CHARGER BATTERY 28-TQFN
标准包装: 2,500
功能: 充电管理
电池化学: 多化学
电源电压: 8 V ~ 28 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 28-WFQFN 裸露焊盘
供应商设备封装: 28-TQFN-EP(5x5)
包装: 带卷 (TR)
Low-Cost Battery Charger
MOSFET Drivers
The DHI output is optimized for driving moderate-sized
power MOSFETs. This is consistent with the variable
duty factor that occurs in the notebook computer envi-
ronment where the battery voltage changes over a wide
range. DHI swings from SRC to DHIV and has a typical
impedance of 1 ? sourcing and 4 ? sinking.
Design Procedure
MOSFET Selection
Choose the p-channel MOSFETs according to the max-
imum required charge current. The MOSFET (P4) must
be able to dissipate the resistive losses plus the switch-
ing losses at both V SRC(MIN) and V SRC(MAX) .
The worst-case resistive power losses occur at the
maximum battery voltage. Calculate the resistive losses
according to the following equation:
where C RSS is the reverse transfer capacitance of the
MOSFET, and I GATE is the peak gate-drive source/sink
current.
These calculations provide an estimate and are not a
substitute for breadboard evaluation, preferably includ-
ing a verification using a thermocoupler mounted on
the MOSFET.
Generally, a small MOSFET is desired to reduce switch-
ing losses at V BATT = V SRC / 2. This requires a tradeoff
between gate charge and resistance. Switching losses
in the MOSFET can become significant when the maxi-
mum AC adapter voltage is applied. If the MOSFET that
was chosen for adequate R DS(ON) at low supply volt-
ages becomes hot when subjected to V SRC(MAX) , then
choose a MOSFET with lower gate charge. The actual
switching losses that can vary due to factors include
the internal gate resistance, threshold voltage, source
inductance, and PC board layout characteristics.
PD Re sis tan ce =
V BATT
V SRC
x I CHG 2 × R DS ( ON )
See Table 3 for suggestions about MOSFET selection.
Schottky Selection
Calculate the switching losses according to the follow-
ing equation:
The Schottky diode conducts the inductor current dur-
ing the off-time. Choose a Schottky diode with the
appropriate thermal resistance to guarantee that it does
PD SWITCHING =
(
x V SRC ( MAX ) x I CHG ? + V SRC ( MAX ) 2 x C RSS
V SRC _ MAX ? ?
V F x I CHG x ? 1 ?
? 2 xQ G
?
? I GATE
f
?
?
1
2
x
)
not overheat:
θ JA <
? V BATT _ MIN ?
?
T J _ MAX ? T A _ MAX
Table 3. Recommended MOSFETs
CHARGE CURRENT (A)
3
2.5
3.5
3.5
4
4
4.5
MOSFET
Si3457DV
FDC658P
FDS9435A
NDS9435A
FDS4435
FDS6685
FDS6675A
PIN-PACKAGE
6-SOT23
6-SOT23
8-SO
8-SO
8-SO
8-SO
8-SO
Q G (nC)
8
12
14
14
24
24
34
MAX
R DSON (m ? )
75
75
80
80
35
35
19
R θ JA
(°/W)
78
78
50
50
50
50
50
T MAX (°C)
+150
+150
+175
+175
+175
+175
+175
24
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