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参数资料
| 型号： | MAX1523 |
| 厂商： | Maxim Integrated Products, Inc. |
| 英文描述： | Simple SOT23 Boost Controllers |
| 中文描述： | 简单的SOT23封装boost控制器 |
| 文件页数： | 6/14页 |
| 文件大小： | 194K |
| 代理商： | MAX1523 |
M
S imple S OT 23 Boost Controllers
6
_______________________________________________________________________________________
guarantees startup with input voltages down to 1.5V at
V
CC
. The startup oscillator has a fixed 25% duty cycle
and will toggle the MOSFET gate and begin boosting
the output voltage. Once the output voltage exceeds
the UVLO threshold, the normal control circuitry is used
and the startup oscillator is disabled. However, N-chan-
nel MOSFETs are rarely specified for guaranteed
R
DS(ON)
with V
GS
below 2.5V; therefore, guaranteed
startup down to 1.5V input will be limited by the MOS-
FET specifications. Nevertheless, the MAX1524 boot-
strapped circuit on the MAX1524 EV kit typically starts
up with input voltage below 1V and no load.
The MAX1522/MAX1523 may also be utilized by con-
necting V
CC
to the output of an independent voltage
regulator between 2.5V and 5.5V to allow operation with
any combination of low or high input and output volt-
ages. In this case, the independent regulator must sup-
ply enough current to satisfy the I
GATE
current as
calculated in the
Power MOSFET Selection
section
when considering the maximum switching frequency as
calculated in the CCM or DCM design procedure.
On-T ime S ET Input
The MAX1522/MAX1523/MAX1524 feature pin-selec-
table fixed on-time control, allowing their operation to
be optimized for various input/output voltage combina-
tions. Connect SET to V
CC
for the 3μs fixed on-time.
Connect SET to GND for the 0.5μs fixed on-time.
The 3μs on-time setting (SET = V
CC
) permits higher
than 80% guaranteed maximum duty factor, providing
improved efficiency in applications with higher step-up
ratios (such as 3.3V boosting to 12V). This setting is
recommended for higher step-up ratio applications.
The 0.5μs on-time setting (SET = GND) permits higher
frequency operation, minimizing the size of the external
inductor and capacitors. The maximum duty factor is
limited to 45% guaranteed, making this setting suitable
for lower step-up ratios such as 3.3V to 5V converters.
S oft-S tart
The MAX1522/MAX1523/MAX1524 have a unique soft-
start mode that reduces inductor current during startup,
reducing battery, input capacitor, MOSFET, and induc-
tor stresses. The soft-start period is fixed at 3.2ms and
requires no external components.
Fault Detec tion
Once the soft-start period has expired, if the output
voltage falls to, or is less than, 50% of its regulation
value, a fault is detected. Under this condition, the
MAX1522 disables the regulator until either
SHDN
is
toggled low or power is removed and reapplied, after
which it attempts to power up again in soft-start. For the
MAX1523, the fault condition is not latched, and soft-
start is repetitively reinitiated until a valid output voltage
is realized. The MAX1524 has a latched fault detection,
but when bootstrapped, the latch will be cleared when
V
CC
falls below 2.37V.
S hutdown Mode
Drive
SHDN
to GND to place the MAX1522/MAX1523/
MAX1524 in shutdown mode. In shutdown, the internal
reference and control circuitry turn off, EXT is driven to
GND, the supply current is reduced to less than 1μA,
and the output drops to one diode drop below the input
voltage. Connect
SHDN
to V
CC
for normal operation.
When exiting shutdown mode, the 3.2ms soft-start is
always initiated.
Undervoltage Loc kout
The MAX1522/MAX1523 have undervoltage lockout
(UVLO) circuitry, which prevents circuit operation and
MOSFET switching when V
CC
is less than the UVLO
threshold (2.37V typ). The UVLO comparator has 70mV
of hysteresis to eliminate chatter due to V
CC
input
impedance.
Applic ations Information
S etting the Output V oltage
The output voltage is set by connecting FB to a resis-
tive voltage-divider between the output and GND
(Figures 1 and 2). Select feedback resistor R2 in the
30k
to 100k
range. R1 is then given by:
where V
FB
= 1.25V.
Design Proc edure
Continuous vs. Disc ontinuous Conduc tion
A switching regulator is operating in continuous con-
duction mode (CCM) when the inductor current is not
allowed to decay to zero. This is accomplished by
selecting an inductor value large enough that the
inductor ripple current becomes less than one half of
the input current. The advantage of this mode is that
peak current is lower, reducing I
2
R losses and output
ripple.
In general, the best transient performance and most of
the ripple reduction and efficiency increase of CCM are
realized when the inductance is large enough to
reduce the ripple current to 30% of the input current at
maximum load. It is important to note that CCM circuits
operate in discontinuous conduction mode (DCM)
R
R
V
V
OUT
FB
1
2
1
=
相关PDF资料 |
PDF描述 |
|---|---|
| MAX1524 | Simple SOT23 Boost Controllers |
| MAX1535A | Highly Integrated Level 2 SMBus Battery Charger |
| MAX1535AETJ | Highly Integrated Level 2 SMBus Battery Charger |
| MAX1535B | MAX1535B Evaluation Kit/MAX1535B Evaluation System |
| MAX1535BEVSYS | MAX1535B Evaluation Kit/MAX1535B Evaluation System |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1523EUT | 制造商:Maxim Integrated Products 功能描述:- Cut Tape Product 制造商:Rochester Electronics LLC 功能描述: |
| MAX1523EUT+ | 制造商:Maxim Integrated Products 功能描述:DC DC CNTRLR SGL-OUT STEP UP 2.5V TO 5.5V 6PIN SOT-23 - Cut Tape Product |
| MAX1523EUT+T | 功能描述:DC/DC 开关控制器 Boost Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1523EUT+T | 制造商:Maxim Integrated Products 功能描述:SOT23 Boost Controller IC |
| MAX1523EUT-T | 功能描述:DC/DC 开关控制器 Boost Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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