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參數(shù)資料
| 型號(hào)： | MAX1802EHJ |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Digital Camera Step-Down Power Supply |
| 中文描述： | 0.75 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PQFP32 |
| 封裝： | 5 X 5 MM, 1 MM HEIGHT, TQFP-32 |
| 文件頁數(shù)： | 18/28頁 |
| 文件大?。?/td> | 469K |
| 代理商： | MAX1802EHJ |
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M
Digital Camera Step-Down
Power Supply
18
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age lockout threshold. The internal core converter, aux-
iliary controllers, and MAX1801 slave controllers each
sink up to 30μA REF current during startup. If multiple
MAX1801 controllers are turned on simultaneously,
ensure that the master voltage reference can provide
sufficient current, or buffer the reference with an appro-
priate unity-gain amplifier.
Oscillator
The oscillator uses a comparator, a 100ns one-shot,
and an internal N-channel MOSFET switch in conjunc-
tion with an external timing resistor and capacitor to
generate the oscillator signal at OSC (Figure 4). The
capacitor voltage exponentially approaches VL from
zero with a time constant given by the R
OSC
C
OSC
product when the switch is open, and the comparator
output becomes high when the capacitor voltage
reaches V
REF
(1.25V). At that time, the one-shot acti-
vates the internal MOSFET switch to discharge the
capacitor within a 100ns interval, and the cycle
repeats. Note that the oscillation frequency changes as
VL changes during startup. The oscillation frequency is
constant while the VL voltage is constant.
Maximum Duty Cycle
The MAX1802
’
s three auxiliary controllers use the saw-
tooth oscillator signal generated at OSC, the voltage at
DCON_, and an internal comparator to limit their maxi-
mum duty cycles (see
Setting the Maximum Duty
Cycle
). Limiting the duty cycle can prevent saturation in
some magnetic components. A low maximum duty
cycle can also force the converter to operate in discon-
tinuous current mode, simplifying design stability at the
cost of a slight reduction in efficiency.
Soft-Start
All the MAX1802 converters feature a soft-start function
that limits inrush current and prevents excessive bat-
tery loading at startup by ramping the output voltage to
the regulation voltage. This is achieved by increasing
the internal reference inputs to the controller transcon-
ductance amplifiers from 0 to the 1.25V reference volt-
age over 1024 oscillator cycles when initial power is
applied or when the controller is enabled.
Overload Protection
The MAX1802
’
s three auxiliary controllers have fault
protection that prevents damage to transformer-cou-
pled or SEPIC circuits due to an output overload condi-
tion. When the output voltage drops out of regulation
for 1024 oscillator clock periods, the auxiliary controller
is disabled to prevent excessive output current. Restart
the controller by cycling the voltage at ON_ or DCON_
to GND and back to the on state. For a step-up appli-
cation, short-circuit current is not limited, due to the DC
current path through the inductor and output rectifier to
the short circuit. If short-circuit protection is required in
a step-up configuration, use a protection device such
as a fuse to limit short-circuit current.
Design Procedure
Setting the Switching Frequency
Choose a switching frequency to optimize external
component size or circuit efficiency for the particular
MAX1802 application. Switching frequencies between
400kHz and 500kHz offer a good balance between
component size and circuit efficiency. Higher frequen-
cies allow smaller components, and lower frequencies
improve efficiency.
The switching frequency is set with an external timing
resistor (R
OSC
) and capacitor (C
OSC
). At the beginning
of a cycle, the timing capacitor charges through the
resistor until it reaches V
REF
. The charge time t
1
is:
t
1
= -R
OSC
(C
OSC
+10pF)
In
[1 - (V
REF
/ V
VL
)]
Once the voltage at OSC reaches V
REF
, it discharges
through an internal switch over time t
2
= 200ns. The
oscillator frequency is f
OSC
= 1 / (t
1
+ t
2
). Set f
OSC
in
the range 100kHz
≤
f
OSC
≤
1MHz. Choose C
OSC
between 47pF and 470pF. Determine R
OSC
from the
relation:
R
OSC
C
OSC
V
REF
(1.25V)
100ns
ONE-SHOT
VL
OSC
MAX1802
Figure 4. Oscillator
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相關(guān)代理商/技術(shù)參數(shù) |
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| MAX1802EHJ+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1802EHJ+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1802EHJ-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1804EUB | 功能描述:電流和電力監(jiān)控器、調(diào)節(jié)器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:Current Regulators 電源電壓-最大:48 V 電源電壓-最小:5.5 V 工作溫度范圍:- 40 C to + 150 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:HPSO-8 封裝:Reel |
| MAX1804EUB+ | 功能描述:電流和電力監(jiān)控器、調(diào)節(jié)器 Feedback Integrator for Power Supply RoHS:否 制造商:STMicroelectronics 產(chǎn)品:Current Regulators 電源電壓-最大:48 V 電源電壓-最小:5.5 V 工作溫度范圍:- 40 C to + 150 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:HPSO-8 封裝:Reel |
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