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參數(shù)資料
| 型號： | MAX1855 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | 數(shù)字信號處理 |
| 英文描述： | Fixed-Point Digital Signal Processor 352-FC/CSP 0 to 0 |
| 中文描述： | 高速、數(shù)字可調(diào)、同步降壓型控制器，集成電壓定位電路 |
| 文件頁數(shù)： | 21/33頁 |
| 文件大?。?/td> | 840K |
| 代理商： | MAX1855 |
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M
High-Speed, Adjustable, Synchronous Step-Down
Controllers with Integrated Voltage Positioning
______________________________________________________________________________________
21
clamped with a Schottky diode to GND to reduce the
negative excursion.
To ensure correct startup, V+ should be present before
V
CC
. If the converter attempts to bring the output into
regulation without V+ present, the fault latch will trip.
After V
CC
rises above 4.2V, an internal digital soft-start
timer begins to ramp up the maximum allowed current
limit. The ramp occurs in five steps: 20%, 40%, 60%,
80%, and 100%, with 100% load current available after
1.7ms ±50%.
Power-Good Output (VGATE)
VGATE is the open-drain output of a window compara-
tor. This power-good output remains high impedance
as long as the output voltage is within ±10% of the reg-
ulation voltage. When the output voltage is greater than
or less than the ±10% window limits, the internal MOS-
FET is activated and pulls the output low. Any fault con-
dition forces VGATE low until the fault is cleared.
VGATE is also low in shutdown, undervoltage lockout,
and during soft-start. For logic-level output voltages,
connect an external pullup resistor between VGATE
and V
CC
(or V
DD
). A 100k
resistor works well in most
applications.
Output Overvoltage Protection
(MAX1716/MAX1855 only)
The overvoltage protection (OVP) circuit is designed to
protect against a shorted high-side MOSFET by draw-
ing high current and activating the battery
’
s protection
circuit. The output voltage is continuously monitored for
overvoltage. If the output exceeds the OVP threshold
(1.9V with the MAX1716, 2.0V with the MAX1855), OVP
is triggered and the circuit shuts down. The DL low-
side gate-driver output latches high until
SHDN
toggles
or V
CC
pulses below 1V. This action turns on the syn-
chronous-rectifier MOSFET with 100% duty cycle and,
in turn, rapidly discharges the output filter capacitor,
forcing the output to ground. If the condition that
caused the overvoltage (such as a shorted high-side
MOSFET) persists, the battery
’
s internal protection cir-
cuit will engage.
OVP can be defeated through the no-fault test mode
(see
No-Fault Test Mode
).
Output Undervoltage Protection
The output undervoltage protection (UVP) function is
similar to foldback current limiting, but employs a timer
rather than a variable current limit. If the regulator
’
s out-
put voltage is under 40% of the nominal value, anytime
after the 20ms undervoltage fault-blanking time, the
PWM is latched off and won
’
t restart until
SHDN
toggles
or V
CC
pulses below 1V.
UVP can be defeated through the no-fault test mode
(see
No-Fault Test Mode
).
Thermal Fault Protection
The MAX1716/MAX1854/MAX1855 feature a thermal
fault protection circuit. When the temperature rises
above +150
°
C, the DL low-side gate-driver output
latches high until
SHDN
toggles or V
CC
pulses below
1V. The threshold has +10
°
C of thermal hysteresis,
which prevents the regulator from restarting until the
die cools off.
No-Fault Test Mode
The over/undervoltage protection features can compli-
cate the process of debugging prototype breadboards
since there are at most a few milliseconds in which to
determine what went wrong. Therefore, a test mode is
provided to disable the OVP, UVP, and thermal shut-
down features, and clear the fault latch if it has been
set. The PWM operates as if
SKIP
were low (SKIP
mode).
The no-fault test mode is entered by sinking 1.5mA
from
SKIP
through an external negative voltage source
in series with a resistor.
SKIP
is clamped to GND with a
silicon diode, so choose the resistor value equal to
(V
FORCE
- 0.65V) / 1.5mA.
Design Procedure
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point. The follow-
ing four factors dictate the design:
Input voltage range:
The maximum value (V+
(MAX)
)
must accommodate the worst-case high AC-adapter
voltage. The minimum value (V+
(MIN)
) must account for
the lowest input voltage after drops due to connectors,
fuses, and battery selector switches. If there is a choice
at all, lower input voltages result in better efficiency.
Maximum load current:
There are two values to con-
sider. The peak load current (I
LOAD(MAX)
) determines
the instantaneous component stresses and filtering
requirements, and thus drives output capacitor selec-
tion, inductor saturation rating, and the design of the
current-limit circuit. The continuous load current
(I
LOAD
) determines the thermal stresses and thus dri-
ves the selection of input capacitors, MOSFETs, and
other critical heat-contributing components. Modern
notebook CPUs generally exhibit I
LOAD
= I
LOAD(MAX)
×
80%.
Switching frequency:
This choice determines the
basic trade-off between size and efficiency. The opti-
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1854EEG | High-Speed, Adjustable, Synchronous Step-Down Controllers with Integrated Voltage Positioning |
| MAX1855EEG | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
| MAX1854 | High-Speed, Adjustable, Synchronous Step-Down Controllers with Integrated Voltage Positioning |
| MAX1857EUA47 | 500mA, Low-Dropout, Ripple-Rejecting LDO in MAX |
| MAX1857 | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1855EEG | 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(fēng)格: 封裝 / 箱體:CPAK |
| MAX1855EEG+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1855EEG-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(fēng)格: 封裝 / 箱體:CPAK |
| MAX1855EVKIT | 功能描述:DC/DC 開關(guān)控制器 Evaluation Kit for the MAX1716 MAX1854 MAX1855 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(fēng)格: 封裝 / 箱體:CPAK |
| MAX1856EUB | 功能描述:電信線路管理 IC RoHS:否 制造商:STMicroelectronics 產(chǎn)品:PHY 接口類型:UART 電源電壓-最大:18 V 電源電壓-最小:8 V 電源電流:30 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VFQFPN-48 封裝:Tray |
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