参数资料
型号: IR3504MTRPBF
厂商: International Rectifier
文件页数: 12/42页
文件大小: 0K
描述: IC CTRL XPHASE3 SVID 32-MLPQ
标准包装: 3,000
系列: XPhase3™
应用: 处理器
电流 - 电源: 10mA
电源电压: 4.75 V ~ 7.5 V
工作温度: 0°C ~ 100°C
安装类型: 表面贴装
封装/外壳: 32-VFQFN 裸露焊盘
供应商设备封装: 32-MLPQ(5x5)
包装: 带卷 (TR)
IR3504
PHASE IC
CLOCK
PULSE
EAIN
PWMRMP
VDAC
GATEH
GATEL
STEADY-STATE
OPERATION
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
DUTY CYCLE DECREASE
DUE TO VIN INCREASE
(FEED-FORWARD)
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
(VCC UV, OCP, VID FAULT)
STEADY-STATE
OPERATION
Figure 6 PWM Operating Waveforms
Body Braking
TM
In a conventional synchronous buck converter, the minimum time required to reduce the current in the inductor in
response to a load step decrease is;
T SLEW =
L * ( I MAX ? I MIN )
V O
The slew rate of the inductor current can be significantly increased by turning off the synchronous rectifier in
response to a load step decrease. The switch node voltage is then forced to decrease until conduction of the
synchronous rectifier’s body diode occurs. This increases the voltage across the inductor from Vout to Vout +
V BODYDIODE . The minimum time required to reduce the current in the inductor in response to a load transient
decrease is now;
T SLEW =
L * ( I MAX ? I MIN )
V O + V BODYDIODE
Since the voltage drop in the body diode is often higher than output voltage, the inductor current slew rate can be
increased by 2X or more. This patent pending technique is referred to as “body braking” and is accomplished
through the “body braking comparator” located in the phase IC. If the error amplifier’s output voltage drops below
the VDAC voltage or a programmable voltage, this comparator turns off the low side gate driver.
Lossless Average Inductor Current Sensing
Inductor current can be sensed by connecting a series resistor and a capacitor network in parallel with the inductor
and measuring the voltage across the capacitor, as shown in Figure 7. The equation of the sensing network is,
v C ( s ) = v L ( s )
1
1 + sR CS C CS
= i L ( s )
R L + sL
1 + sR CS C CS
Usually the resistor Rcs and capacitor Ccs are chosen so that the time constant of Rcs and Ccs equals the time
constant of the inductor which is the inductance L over the inductor DCR (R L ). If the two time constants match, the
voltage across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense
resistor with the value of R L was used. The mismatch of the time constants does not affect the measurement of
inductor DC current, but affects the AC component of the inductor current.
Page 12
July 28, 2009
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