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參數(shù)資料
| 型號(hào)： | SP6121EB |
| 英文描述： | Demo Board Manual |
| 中文描述： | 演示板手冊(cè) |
| 文件頁(yè)數(shù)： | 7/16頁(yè) |
| 文件大?。?/td> | 358K |
| 代理商： | SP6121EB |
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Date: 5/25/04
SP6121 Low Voltage, Synchronous Step Down PWM Controller Copyright 2004 Sipex Corporation
7
Over Current Protection
Over current protection on the SP6121 is imple-
mented through detection of an excess voltage
condition across the high side PMOS switch
during conduction. This is typically referred to
as high side R
DS(ON)
detection and eliminates the
need of an external sense resistor. The over
current comparator charges an internal sam-
pling capacitor each time V
(ISET)
- V
(ISENSE)
exceeds the 160mV (typ) internal threshold and
the PDRV voltage is low. The discharge/charge
current ratio on the sampling capacitor is about
2%. Therefore, provided that the over current
condition persists, the capacitor voltage will be
pumped up during each time PDRV switches
low. This voltage will trigger an over current
condition upon reaching a CMOS inverter thresh-
old. There are many advantages to this ap-
proach. First, the filtering action of the gated S/
H scheme protects against false and undesirable
triggering that could occur during a minor tran-
sient overload condition or supply line noise.
Furthermore, the total amount of time to trigger
the fault depends on the on-time of the PMOS
switch. Ten, 1
μ
s pulses are equivalent to twenty,
500ns pulses or one, 10
μ
s pulse, however, de-
pending on the period, each scenario takes a
different amount of total time to trigger a fault.
Therefore, the fault becomes an indicator of
average power in the PMOS switch.
Although the 160 mV internal threshold is fixed,
the overall R
DS(ON)
detection voltage can be
increased by placing a resistor from I
SET
to the
source of the PMOS. A 30
μ
A sink current pro-
grams the additional voltage.
In order for the current limit circuit to operate
properly and accurately, the I
SET
and I
SENSE
pins
must be Kelvin connected to the high side
PMOS’s source and drain pins.
The 160mV threshold and 30
μ
A I
SET
current
have 3300 ppm/
°
C temperature coefficients in
an effort to first order match the thermal charac-
teristics of the R
DS(ON)
of the PMOS switch. It
assumed that the SP6121 will be used in com-
pact designs where there is a high amount of
thermal coupling between the PMOS and the
controller.
Output Drivers
The SP6121, unlike some other bipolar control-
ler IC’s, incorporates gate drivers with rail-to-
rail swing that help prevent spurious turn on due
to capacitive coupling. The driver stage consists
of one high side PMOS, 4
driver, PDRV, and
one low side, 4
, NFET driver, NDRV, opti-
mized for driving external power MOSFET’s in
a synchronous buck topology. The output driv-
ers also provide gate drive non-overlap mecha-
nism that provides a dead time between PDRV
and NDRV transitions to avoid potential shoot-
through problems in the external MOSFET’s.
Figure 3 shows typical waveforms for the output
drivers. As with all synchronous designs, care
must be taken to ensure that the MOSFETs are
properly chosen for non-overlap time, enhance-
ment gate drive voltage, “on” resistance R
DS(ON)
,
reverse transfer capacitance Crss, input voltage
and maximum output current.
TIME
NDRV
Voltage
PDRV
Voltage
V(V
CC
)
- V(Diode) V
~ 0 V
Voltage
SWN
V(V
CC
)
0 V
0 V
V(V
CC
=V
IN
)
Vcc-2 V
NON-OVERLAP
2 V
10 %
RISE TIME
10 %
90 %
FALL TIME
NDRV(PDRV)
PDRV(NDRV)
5 V
90 %
5 V
GATE DRIVER TEST CONDITIONS
Figure 3. SP6121 Output Driver Waveforms.
THEORY OF OPERATION: continued
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| SP6122 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, Micro 8, PFET, Buck Controller Ideal for 1A to 5A, Small Footprint, DC-DC Power Converters |
| SP6122_04 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, Micro 8, PFET, Buck Controller Ideal for 1A to 5A, Small Footprint, DC-DC Power Converters |
| SP6122ACU | 制造商:Rochester Electronics LLC 功能描述: 制造商:Exar Corporation 功能描述: |
| SP6122ACU/TR | 制造商:Exar Corporation 功能描述: |
| SP6122ACU-1.5 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, Micro 8, PFET, Buck Controller Ideal for 1A to 5A, Small Footprint, DC-DC Power Converters |
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