IRU3073CQTR【PDF 6/21 页】IC REG DL BCK/LINEAR 16-QSOP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录40

2页 3页 4页 5页 [6页]7页 8页 9页 10页

Rev. 1.0

09/17/03

IRU3073

www.irf.com

LDO Controller

The LDO section is powered directly from Vcc. The out-

put of LDO can be set as low as 0.8V and can be pro-

grammed to higher voltages by using two external resis-

tors.

Supply Voltage Under-Voltage Lockout

The under-voltage lockout circuit assures that the

MOSFET driver outputs, remain in the off state when-

ever the supply voltage drops below set parameters. Lock-

out occurs if Vcc or VcH fall below 4.0V and 3.3V re-

spectively. Normal operation resumes once these volt-

ages rise above the set values.

Shutdown

The PWM section can be shutdown by pulling the soft-

start pin below 0.4V. The control MOSFET turns off and

the synchronous MOSFET turns on during shutdown.

Over-Current Protection

Over-current protection is achieved with a cycle by cycle

scheme and it is performed by sensing current through

the RDS(ON) of low side MOSFET. As shown in Figure 5,

an external resistor (RSET) is connected between OCSet

pin and the drain of low side MOSFET (Q2) and sets the

current limit set point. The internal current source devel-

ops a voltage across RSET. When the low side switch is

turned on, the inductor current flows through the Q2 and

results a voltage which is given by:

Figure 5 - Diagram of the over current sensing.

When voltage VOCSET is below zero, the current sensing

comparator flips and disables the oscillator. The high

side MOSFET is turned off and the low side MOSFET is

turned on until the inductor current reduces to below

current set value. The critical inductor current can be

calculated by setting:

CSS = 20mA3TSTART/1V

20mA3TSTART/CSS = 2V-1V

Soft-Start

Voltage

Voltage at negative input

of Error Amp and Feedback

UVLO comparator

Voltage at Fb1 pin

Current flowing

into Fb1 pin

64uA

0uA

0.8V

E1.6V

0.8V

E2V

E1V

Output of UVLO

POR

The feedback voltage increases linearly as the injecting

current goes down. The injecting current drops to zero

when soft-start voltage is around 2V and the output volt-

age goes into steady state.

As shown in Figure 4, the positive pin of feedback UVLO

comparator is always higher than 0.4V, therefore, feed-

back UVLO is not functional during soft-start.

Figure 4 - Theoretical operation waveforms

during Soft-Start.

From this analysis, the output start-up time is defined

as when soft-start capacitor voltage increases from 1V

to 2V. The start-up time will be dependent on the size of

the external soft-start capacitor and can be estimated

by:

For a given start up time, the soft-start capacitor can be

calculated as:

MOSFET Drivers

The driver capabilities of both high and low side drivers

are optimized to maintain fast switching transitions. They

are sized to drive a MOSFET that can deliver up to 20A

output current.

The low side MOSFET diver is supplied directly by VCC

while the high side driver is supplied by VC.

An internal dead time control is implemented to prevent

cross-conduction and allows the use of several kinds of

MOSFETs.

VOCSET = IOCSET3RSET-RDS(ON)3iL ---(1)

RSET

IRU3073

OCSet

IOCSET

VOUT

Osc

ISET = IL(CRITICAL) = ---(2)

RSET3IOCSET

RDS(ON)

VOCSET = IOCSET3RSET - RDS(ON)3IL = 0

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式