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參數(shù)資料
| 型號： | MAX1994ETM |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Step-Down Controllers Plus Linear- Regulator Controller for Notebook Computers |
| 中文描述： | DUAL SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, CQCC48 |
| 封裝： | 7 X 7 MM, 0.80 MM HEIGHT, THIN, QFN-48 |
| 文件頁數(shù)： | 42/49頁 |
| 文件大小： | 983K |
| 代理商： | MAX1994ETM |
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M
Dual Step-Down Controllers Plus Linear-
Regulator Controller for Notebook Computers
42
______________________________________________________________________________________
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (I
RMS
) imposed by the switching currents
defined by the following equation:
The RMS input currents for BUCK1 and BUCK2 can be
calculated using the above equation. Use the sum
of these two currents as the total RMS current. Note
that this is a very conservative estimation because the
two regulators are never in phase 100% of the time.
The actual RMS current is always lower than the
calculated value.
For most applications, nontantalum chemistries (ceramic
or OSCON) are preferred due to their resilience to
inrush surge currents typical of systems with a switch
or a connector in series with the battery. If the
MAX1816/MAX1994 operate as the second stage of a
two-stage power conversion system, tantalum input
capacitors are acceptable. In either configuration,
choose an input capacitor that exhibits less than +10
°
C
temperature rise at the RMS input current for optimal
circuit longevity.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
challenge of obtaining high load-current capability
(>12A) when using high-voltage (>20V) AC adapters.
Low-current applications usually require less attention.
The high-side MOSFET (Q1 in Figure1) must be able to
dissipate the resistive losses plus the switching losses
at both V
IN(MIN)
and V
IN(MAX)
. Calculate both of these
sums. Ideally, the losses at V
IN(MIN)
should be roughly
equal to the losses at V
IN(MAX)
, with lower losses in
between. If the losses at V
IN(MIN)
are significantly high-
er than the losses at V
IN(MAX)
, consider increasing the
size of Q1. Conversely, if the losses at V
IN(MAX)
are sig-
nificantly higher than the losses at V
IN(MIN)
, consider
reducing the size of Q1. If V
IN
does not vary over a
wide range, the minimum power dissipation occurs
where the resistive losses equal the switching losses.
Choose a low-side MOSFET (Q2) that has the lowest
possible R
DS(ON)
, comes in a moderate-sized package
(i.e., two or more 8-pin SOs, DPAKs, or D
2
PAKs), and is
reasonably priced. Ensure that the MAX1816/MAX1994
DL_ gate driver can drive Q2; in other words, check that
the dV/dt caused by Q1 turning on does not pull up the
gate of Q2 due to drain-to-gate capacitance, causing
cross-conduction problems. Switching losses are not an
issue for the low-side MOSFET, since it is a zero-voltage
switched device when used in the buck topology.
MOSFET Power Dissipation
The high-side MOSFET conduction power dissipation
due to on-state channel resistance is:
Generally, a small high-side MOSFET is desired to
reduce switching losses at high input voltages.
However, the R
DS(ON)
required to stay within package
power-dissipation limits often constrains how small the
MOSFET can be.
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the
CV
2
f
SW
switching-loss equation. If the high-side MOSFET
chosen for adequate R
DS(ON)
at low battery voltages
becomes extraordinarily hot when subjected to V
IN(MAX)
,
reconsider the MOSFET selection.
Calculating the power dissipation in Q1 due to switch-
ing losses is difficult since it must allow for difficult
quantifying factors that influence the turn-on and turn-
off times. These factors include the internal gate resis-
tance, gate charge, threshold voltage, source induct-
ance, and PC board layout characteristics. The follow-
ing switching-loss calculation provides only a very
rough estimate and is no substitute for breadboard
evaluation and thermal measurements:
where C
RSS
is the reverse transfer capacitance of Q1
and I
GATE
is the peak gate-drive source/sink current
(1.5A typ for BUCK1, 0.75A typ for BUCK2).
For the low-side MOSFET (Q2), the worst-case power
dissipation always occurs at maximum battery voltage:
The worst case for MOSFET power dissipation occurs
under heavy overloads that are greater than I
LOAD(MAX)
but are not quite high enough to exceed the current limit
and cause the fault latch to trip. To protect against this
possibility,
“
overdesign
”
the circuit to tolerate:
I
LOAD
= I
LIMIT(HIGH )
+ (LIR/2)
I
LOAD(MAX)
PD Q
V
V
I
R
OUT
IN MAX
(
LOAD
DS ON
(
(
)
)
)
2
1
2
2
=
×
×
PD Q
Switching
C
V
f
I
I
RSS
IN MAX
(
SW
LOAD
GATE
(
_
)
)
1
2
=
×
×
×
PD Q
Conduction
V
V
I
R
OUT
IN
LOAD
DS ON
(
(
_
)
)
1
2
1
=
×
×
I
I
V
V
V
V
RMS
LOAD
OUT
IN
OUT
IN
=
(
)
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1816 | Replaced by TMS320VC5506 : Digital Signal Processors 144-LQFP |
| MAX1816ETM | Replaced by TMS320VC5506 : Digital Signal Processors 144-LQFP |
| MAX199AEWI | Fixed-Point Digital Signal Processor 532-FCBGA |
| MAX199AMYI | Circular Connector; No. of Contacts:18; Series:MS27505; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Socket; Circular Shell Style:Box Mount Receptacle RoHS Compliant: No |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1994ETM+ | 功能描述:DC/DC 開關(guān)控制器 Integrated Circuits (ICs) RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM+T | 功能描述:DC/DC 開關(guān)控制器 Integrated Circuits (ICs) RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994ETM-T | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1994EVKIT | 功能描述:DC/DC 開關(guān)控制器 Evaluation Kit for the MAX1816 MAX1980 MAX1994 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| MAX1995EGI | 功能描述:顯示驅(qū)動器和控制器 RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
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