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参数资料
| 型号： | IR3621FTR |
| 厂商： | International Rectifier |
| 文件页数： | 13/29页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 28TSSOP |
| 产品变化通告： | (EP) Parts Discontinuation 25/May/2012 |
| 标准包装： | 0 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 345kHz |
| 占空比： | 86.5% |
| 电源电压： | 5.5 V ~ 14.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 28-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 标准包装 |
| 产品目录页面： | 1383 (CN2011-ZH PDF) |
| 配用： | IRDC3621-ND - BOARD EVAL DUAL SYNC BUCK CTRLR |
| 其它名称： | IR3621FDKR |
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IR3621 & (PbF)
t r + t f × I LOAD
×
P COND (Upper Switch) = I LOAD × R DS(on) × D ×?
The gate drive requirement is almost the same for both
MOSFETs. Logic-level transistors can be used and cau-
tion should be taken with devices at very low V GS to pre-
vent undesired turn-on of the complementary MOSFET,
which results in a shoot-through.
The total power dissipation for MOSFETs includes con-
duction and switching losses. For the Buck converter,
the average inductor current is equal to the DC
load current. The conduction loss is defined as:
2
V DS(OFF)
P SW = ---(9)
2 T
Where:
V DS(OFF) = Drain to Source Voltage at off time
t r = Rise Time
t f = Fall Time
T = Switching Period
I LOAD = Load Current
V DS
90%
P COND (Lower Switch) = I LOAD × R DS(on) × (1 - D) ×?
2
? = R DS(on) Temperature Dependency
10%
The R DS(ON) temperature dependency should be consid-
ered for the worst case operation. This is typically given
V GS
t d (ON)
t r
t d (OFF)
t f
in the MOSFET data sheet. Ensure that the conduction
losses and switching losses do not exceed the package
Figure 13 - Switching time waveforms.
ratings or violate the overall thermal budget.
From IRF7821 data sheet we obtain:
Choose IRF7821 for control MOSFETs and IRF8113 for
synchronous MOSFETs. These devices provide low on-
resistance in a compact SOIC 8-Pin package.
The MOSFETs have the following data:
IRF7821
t r = 2.7ns
t f = 7.3ns
These values are taken under a certain condition test.
For more details please refer to the IRF7821 data sheet.
IRF7821
IRF8113
V DSS = 30V
R DS(on) = 9m ?
V DSS = 30V
R DS(on) = 6m ?
By using equation (9), we can calculate the total switch-
ing losses.
P SW(TOTAL,2.5V) = 0.18W
The total conduction losses for each output will be:
P CON(TOTAL, 2.5V) = P CON(UPPER) + P CON(LOWER)
P CON(TOTAL, 2.5V) = 1.0W
P CON(TOTAL, 1.8V) = P CON(UPPER) + P CON(LOWER)
P CON(TOTAL, 1.8V) = 1.0W
The switching loss is more difficult to calculate, even
though the switching transition is well understood. The
reason is the effect of the parasitic components and
switching times during the switching procedures such
as turn-on / turnoff delays and rise and fall times. The
control MOSFET contributes to the majority of the switch-
ing losses in a synchronous Buck converter. The syn-
chronous MOSFET turns on under zero voltage condi-
tions, therefore, the switching losses for synchronous
MOSFET can be neglected. With a linear approxima-
tion, the total switching loss can be expressed as:
P SW(TOTAL,1.8V) = 0.18W
Programming the Over-Current Limit
The over-current threshold can be set by connecting a
resistor (R SET ) from drain of low side MOSFET to the
OCSet pin. The resistor can be calculated by using equa-
tion (3).
The R DS(on) has a positive temperature coefficient and it
should be considered for the worse case operation.
R DS(on) = 6m ?× 1.5 = 9m ?
I SET ? I O(LIM) = 10A × 1.5 = 15A
(50% over nominal output current)
This results to:
R SET = R 1 =R 6 =6.75K ?
This resistor must be placed close to the IC, place a
small ceramic capacitor from this pin to ground for noise
rejection purposes.
www.irf.com
13
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| IR3621FTRPBF | 功能描述:DC/DC 开关控制器 2-PHASE DUAL SYNC PWM CTRLLER RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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