參數(shù)資料
型號(hào)： DS1244Y
廠商： MAXIM INTEGRATED PRODUCTS INC
元件分類： Timer or RTC
英文描述： 0 TIMER(S), REAL TIME CLOCK, PDIP28
封裝： 0.740 INCH, PLASTIC, DIP-28
文件頁(yè)數(shù)： 5/21頁(yè)
文件大小： 1965K
代理商： DS1244Y
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
13
Detailed Description
The MAX17129/MAX17149 are high-efficiency drivers for
arrays of white LEDs. They contain a Quick-PWM step-up
controller, a 3.8V linear regulator, PWM dimming control
circuit, internal power MOSFET, and six regulated current
sources. Figure 2 shows the devices' functional diagram.
When enabled, the step-up controller boosts the output
voltage to provide sufficient headroom for the current
sources to regulate their respective string currents. The
devices feature adjustable pseudo-fixed frequency,
which allows trade-offs between external component
size and operating efficiency.
Both devices have a wide input voltage range, from 6V
to 26V; when IN and VCC are tied together, the range is
extended to the 3V to 5.5V range.
Both devices can implement two different brightness-
control methods: PWM dimming and hybid dimming.
When in direct PWM mode, the LED brightness is con-
trolled by the frequency and duty cycle of the square-
wave signal applied on the BRT pin. When in hybrid
dimming mode, the amplitude of LED current is adjusted
to 25% of the full-scale value, which is set by the resistor
from the ISET pin to GND.
The devices have multiple features to protect the control-
ler from faulty conditions. A separate feedback loop lim-
its the output voltage in all circumstances. The devices
monitor each FB_ voltage during the operation. If one or
more strings are open, the corresponding FB_ voltages
are pulled below 700mV (max) and the OVP output is
forced to increase over the overvoltage threshold; once
the open fault is detected, the respective current sources
are so disabled. When one or more LEDs are shorted
and the related FB_ voltage exceeds 8V, short fault is
detected and the respective current source is disabled.
When in LED open or short conditions, only the faulty
string is disabled while other strings can still operate
normally.
The devices also feature other kinds of fault protec-
tions, which are overcurrent, output overvoltage, and
thermal shutdown. The cycle-by-cycle current limit is to
provide consistent operation and soft-start protection;
when in overcurrent condition, the devices latch off after
a 0.8ms typical (at full brighteness) overcurrent fault
timer expires. An output overvoltage protection prevents
the devices from switching when the output exceeds a
threshold voltage; A thermal-shutdown circuit prevents
the devices from excessive power dissipation.
Quick-PWM Step-Up Controller
The step-up converter is a Quick-PWM type for good
performance. The Quick-PWM control architecture is
a pseudo-fixed-frequency, constant-off-time, current-
mode regulator. The control algorithm is simple: the
internal switch off-time is determined solely by a one-
shot whose period is inversely proportional to output volt-
age, and directly proportional to input voltage. Figure 4
shows the functional diagram with Quick-PWM control
architecture. The off-time one-shot triggers when the
error comparator goes low, the inductor current is below
the current-limit threshold, and the minimum on-time
one-shot times out.
Once the step-up starts up, the output voltage is regu-
lated by selecting the minimum FB voltage between the
detected active current-balancer outputs and compar-
ing it to the OVP divider. The soft-start mechanism is
inserted to provide a controlled current profile during
step-up startup phases.
Off-Time One-Shot
The Quick-PWM core contains a fast, low-jitter, adjust-
able one-shot that sets the internal MOSFETs off-time.
The one-shot varies the off-time in response to the input
and feedback voltages. The internal switch off-time is
inversely proportional to the output voltage (VOVP), and
proportional to the input voltage (VIN):
IN
OFF
OVP
V
T
V
K
=
×
where the switching period (K) is set by the FSEL pin.
This algorithm results in a nearly constant switching
frequency and balanced inductor currents despite the
lack of a fixed-frequency clock generator. The benefits
of a near-constant switching frequency are two-fold: first,
the frequency can be selected to avoid noise-sensitive
regions; second, the inductor ripple-current operating
point remains relatively constant, resulting in easy design
methodology and predictable output-voltage ripple. The
off-time one-shots have good accuracy at the operating
points specified in the Electrical Characteristics table.
Off-times translate only roughly to switching frequencies.
The off-times guaranteed in the Electrical Characteristics
table are influenced by internal switching delays. Resistive
losses, including the inductor, internal MOSFET, the for-
ward voltage of the output diode, output capacitor ESR,
and PCB copper losses in the output and ground tend to
raise the switching frequency at higher output currents.
相關(guān)PDF資料
PDF描述
DS1245AB-100 128K X 8 NON-VOLATILE SRAM MODULE, 100 ns, DMA32
DS1245Y-120 128K X 8 NON-VOLATILE SRAM MODULE, 120 ns, DMA32
DS1245AB-85 128K X 8 NON-VOLATILE SRAM MODULE, 85 ns, DMA32
DS1245Y-85 128K X 8 NON-VOLATILE SRAM MODULE, 85 ns, DMA32
DS1245Y-70 128K X 8 NON-VOLATILE SRAM MODULE, 70 ns, DMA32
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
DS1244Y120 制造商:Maxim Integrated Products 功能描述:
DS1244Y-120 制造商:Maxim Integrated Products 功能描述:
DS1244Y-150 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述:
DS1244Y-200 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:256K NV SRAM with Phantom Clock
DS1244Y-70 功能描述:實(shí)時(shí)時(shí)鐘 RoHS:否 制造商:Microchip Technology 功能:Clock, Calendar. Alarm RTC 總線接口:I2C 日期格式:DW:DM:M:Y 時(shí)間格式:HH:MM:SS RTC 存儲(chǔ)容量:64 B 電源電壓-最大:5.5 V 電源電壓-最小:1.8 V 最大工作溫度:+ 85 C 最小工作溫度: 安裝風(fēng)格:Through Hole 封裝 / 箱體:PDIP-8 封裝:Tube
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