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| 型號(hào)： | UB2012AG-S08-R |
| 廠商： | UNISONIC TECHNOLOGIES CO LTD |
| 元件分類： | 電源管理 |
| 英文描述： | POWER SUPPLY SUPPORT CKT, PDSO8 |
| 封裝： | HALOGEN FREE, SOP-8 |
| 文件頁(yè)數(shù)： | 6/17頁(yè) |
| 文件大小： | 315K |
| 代理商： | UB2012AG-S08-R |
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UB2012
Preliminary
LINEAR INTEGRATED CIRCUIT
UNISONICTECHNOLOGIESCO.,LTD
14 of 17
www.unisonic.com.tw
QW-R121-018 .b
APPLICATION INFORMATION(Cont.)
SELECTING AN EXTERNAL PASS-TRANSISTOR (Cont.)
P-CHANNEL MOSFET:
Selection steps for a P-channel MOSFET: Example: VI = 5.5 V, I(REG) = 500mA, 4.2-V single-cell Li-Ion (UTC
UB2012
C). VI is the input voltage to the charger and I (REG) is the desired charge current (see Figure 4).
1. Determine the maximum power dissipation, PD , in the transistor.
The worst case power dissipation happens when the cell voltage, V (BAT), is at its lowest (typically 3 V at the
beginning of current regulation phase) and VI is at its maximum.
Where VD is the forward voltage drop across the reverse-blocking diode (if one is used), and VCS is the voltage
drop across the current sense resistor.
PD = (VI-VD-V(CS)-V(BAT))×I(REG)
(10)
PD = (5.5-0.4-0.1-3)×0.5A
PD = 1W
2.
Determine the package size needed in order to keep the junction temperature below the manufacturer’s
recommended value, TJMAX. Calculate the total theta, θ(°C/W), needed.
θJA =
D
A(MAX)
MAX(J)
P
)
T
-
(T
(11)
θJA =
1
)
40
-
150
(
θJA = 110°C/W
Now choose a device package with a theta at least 10% below this value to account for additional thetas other
than the device. A SOP-8 package, for instance, has typically a theta of 70°C/W.
3. Select a drain-source voltage, V(DS), rating greater than the maximum input voltage. A 12 V device will be
adequate in this example.
4. Select a device that has at least 50% higher drain current (ID) rating than the desired charge current I(REG).
5. Verify that the available drive is large enough to supply the desired charge current.
V(GS) = (VD+V(CS)+VOL(CC))-VI
(12)
V(GS) = ( 0.4+0.1+1.5)-5.5
V(GS) = -3.5
Where V(GS) is the gate-to-source voltage, VD is the forward voltage drop across the reverse-blocking diode (if
one is used), and VCS is the voltage drop across the current sense resistor, and VOL(CC) is the CC pin output low
voltage specification for the UTC UB2012.
Select a MOSFET with gate threshold voltage, V(GSTH), rating less than the calculated V(GS).
Now choose a P-channel MOSFET transistor that is rated for VDS≤-15 V, θJA ≤110°C /W, ID ≥1 A, V(GSTH)≥-3.5
V and in a SOP package.
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