3)  When GATE reaches the gate threshold voltage of
the power MOSFET, V
OUT
begins to ramp back
down toward V
EE
. In the interval where GATE is
below the MOSFET threshold, the MOSFET is off
and V
OUT
will droop depending on the RC time con-
stant of the load. [V
OUT
ramp]
4)  When V
OUT
ramps below 74% V
CB
, the GATE is
rapidly pulled to full enhancement and the OV GATE
cycle is complete. [Full enhancement]
OV GATE Cycle to Fault management:
1) Same as step 1 above. [GATE pulldown]
2) Same as step 2 above. [GATE turn-on]
3) Same as step 3 above. [V
OUT
ramp]
4) If GATE ramps to 90% of full enhancement and
V
OUT
remains above 74% V
CB
, GATE is rapidly
pulled to V
EE
, fault management is initiated, and
PGOOD is deasserted. [Fault management]
GATE Output
GATE is a complex output structure and its condition at
any moment is dependent on various timing
sequences in response to multiple inputs. A diode to
V
EE
prevents negative excursions. For positive excur-
sions, the states are:
1)  Power-off with 2V clamp.
2)  8& pulldown to V
EE.
a.  Continuous during startup delay and during
fault conditions.
b.  Pulsed following detected step or OV
condition.
3)  Floating with 16V clamp [prior to GATE ramp].
4)  52礎(chǔ) current source with 16V clamp [GATE ramp].
5)  Pullup to internal 10V supply with 16V clamp [full
enhancement].
Appendix B
Step Monitor Component
Selection Analysis
As mentioned previously in the Setting the Circuit-
Breaker and Short-Circuit Thresholds section, the AC
response from V
IN
to V
OUT
is dependent on the para-
sitics of the load. This is especially true for the load
capacitor in conjunction with the power MOSFETs
R
DS(ON)
. The load capacitor (with parasitic ESR and
LSR) and the power MOSFETs R
DS(ON)
can be mod-
eled as a heavily damped second-order system. As
such, this system functions as a bandpass filter from
V
IN
to V
OUT
limiting the ability of V
OUT
to follow the V
IN
ramp. STEP_MON lags the V
IN
ramp with a first-order
RC response, while V
OUT
lags with an overdamped
second-order response.
Given a positive V
IN
ramp with a ramp rate of dV/dt, the
approximate response of V
OUT
to V
IN
is:
V
OUT
(t) = (dV/dt) x ?/DIV>
C
x (1-e
(-t / 腖,eqv)
)
+ R
DS(ON)
x I
LOAD
(Equation 1)
where ?/DIV>
C
= C
LOAD
x R
DS(ON)
.
Equation 1 is a simplification for the overdampened
second-order response of the load to a ramp input, ?/DIV>
C
= C
LOAD
x R
DS(ON)
and corresponds to the ability of
the load capacitor to transfer dV/dt current to the fully
enhanced power MOSFETs R
DS(ON)
. The equivalent
time constant of the load (?/DIV>
L,eqv
) accounts for the para-
sitic series inductance and resistance of the capacitor
and board interconnect. To characterize the load
dynamic response to V
IN
ramps, determine ?/DIV>
L,eqv
empirically with a few tests.
Similarly, the response of STEP_MON to a V
IN
ramp is:
V
STEP_MON
(t) = (dV/dt) x ?/DIV>
STEP
x (1-e
(-t / 腟TEP)
)
+ 10礎(chǔ) x R
STEP_MON
(Equation 2)
where ?/DIV>
STEP
= R
STEP_MON
x C
STEP_MON.
For proper step detection, V
STEP_MON
must exceed
STEP
TH
prior to V
OUT
reaching V
SC
or within 1.4ms of
V
OUT
reaching V
CB
(or overall V
IN
ramp rates anticipat-
ed in the application). It is impossible to give a fixed set
of design guidelines that rigidly apply over the wide
array of applications using the MAX5938. There are,
however, limiting conditions and recommendations that
should be observed.
One limiting condition that must be observed is to
ensure that the STEP_MON time constant, ?/DIV>
STEP
, is not
so low that at the lowest ramp rate, the anticipated
STEP
TH
cannot be obtained. The product (dV/dt) x
?/DIV>
STEP
= ?/DIV>
STEP_MON,MAX
, is the maximum differential
voltage at STEP_MON if the V
IN
ramp were to continue
indefinitely. A related condition is setting the
STEP_MON voltage below STEP
TH
with adequate mar-
gin, V
STEP_MON
, to accommodate the tolerance of
both I
STEP_OS
(?%) and R
STEP_MON
. In determining
?/DIV>
STEP_MON
, use the 9.2礎(chǔ) limit to ensure sufficient mar-
gin with worst-case I
STEP_OS
.
The margin of V
OUT
(with respect to V
SC
and V
CB
) is
set when R
CB_ADJ
is selected as described in the
Setting the Circuit-Breaker and Short-Circuit Thresholds
section. This margin may be lower at one of the temper-
ature extremes and if so, that value should be used in
the following discussion. These margins will be called
-48V Hot-Swap Controller with V
IN
Step Immunity,
No R
SENSE
, and Overvoltage Protection
22   ______________________________________________________________________________________
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
MAX5938LEEE+ |
功能描述:熱插拔功率分布 48V- Hot-Swap Controller RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
MAX5938LEEE+T |
功能描述:熱插拔功率分布 48V- Hot-Swap Controller RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
MAX5938LEEE-T |
功能描述:熱插拔功率分布 RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
MAX5939AESA |
功能描述:熱插拔功率分布 RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
MAX5939AESA+ |
功能描述:熱插拔功率分布 48V- Hot-Swap Controller RoHS:否 制造商:Texas Instruments 產(chǎn)品:Controllers & Switches 電流限制: 電源電壓-最大:7 V 電源電壓-最小:- 0.3 V 工作溫度范圍: 功率耗散: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:MSOP-8 封裝:Tube |
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