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| 型号： | MAX1777EEI+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 28/32页 |
| 文件大小： | 0K |
| 描述： | IC REG QD BUCK/LINEAR 28QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 拓扑： | 降压（降压）（2），线性（LDO）（2） |
| 功能： | 任何功能 |
| 输出数： | 4 |
| 频率 - 开关： | 200kHz ~ 500kHz |
| 电压/电流 - 输出 1： | 控制器 |
| 电压/电流 - 输出 2： | 控制器 |
| 电压/电流 - 输出 3： | 3.3V，100mA |
| 带 LED 驱动器： | 无 |
| 带监控器： | 无 |
| 带序列发生器： | 是 |
| 电源电压： | 4.5 V ~ 24 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 28-QSOP |
| 包装： | 带卷 (TR) |
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High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
an MBR0530 (500mA-rated) type for loads up to 1.5A, a
1N5819 type for loads up to 3A, or a 1N5822 type for
loads up to 10A. The rectifier’s rated reverse breakdown
voltage must be at least equal to the maximum input volt-
age, preferably with a 20% derating factor.
Boost Supply Diode
A signal diode, such as a 1N4148, works well in most
applications. Use a small (20mA) Schottky diode for
slightly improved efficiency and dropout characteris-
tics, if the input voltage can go below 6V. Do not use
large power diodes, such as 1N5817 or 1N4001, since
high-junction capacitance can force LDO5 to excessive
voltages.
Applications Information
where V DROP1 and V DROP2 are the parasitic voltage
drops in the discharge and charge paths (see the On-
Time One-Shot section), t OFF(MIN) is from the EC table,
and K is taken from Table 2. The absolute minimum
input voltage is calculated with h = 1.
Operating frequency must be reduced or h must be
increased and output capacitance added to obtain an
acceptable V SAG if calculated V+ (MIN) is greater than
the required minimum input voltage. Calculate V SAG to
be sure of adequate transient response if operation
near dropout is anticipated.
Dropout Design Example
MAX1977: With V OUT5 = 5V, fsw = 400kHz, K = 2.25μs,
t OFF(MIN) = 350ns, V DROP1 = V DROP2 = 100mV, and h = 1.5,
? 0 . 35 μ s × 1 . 5 ?
1 ? ? ?
Dropout Performance
The output voltage-adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 350ns
(max) minimum off-time one-shot. Use the slower 5V
SMPS for the higher of the two output voltages for best
dropout performance in adjustable feedback mode. The
the minimum V+ is:
V + ( MIN ) = ( 5 V + 0 . 1 V )
? 2 . 25 μ s ?
+ 0 . 1 V ? 0 . 1 V = 6 . 65 V
( ) V 1 . 0
? 0 . 35 μ s × 1 ?
duty-factor limit must be calculated using worst-case val-
ues for on- and off-times, when working with low input
voltages. Manufacturing tolerances and internal propaga-
tion delays introduce an error to the t ON K factor. Also,
keep in mind that transient response performance of
buck regulators operated close to dropout is poor, and
bulk output capacitance must often be added (see the
Calculating with h = 1 yields:
5 V +
V + ( MIN ) =
1 ? ? ?
? 2 . 25 μ s ?
+ 0 . 1 V ? 0 . 1 V = 6 . 04 V
V SAG equation in the Output Capacitor Selection section).
The absolute point of dropout occurs when the inductor
current ramps down during the minimum off-time
( ? I DOWN ) as much as it ramps up during the on-time
( ? I UP ). The ratio h = ? I UP / ? I DOWN indicates the ability to
slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
Therefore, V+ must be greater than 6.65V. A practical
input voltage with reasonable output capacitance
would be 7.5V.
MAX1658/
the inductor current is less able to increase during each
switching cycle and V SAG greatly increases unless
additional output capacitance is used.
DH_
V+
MAX1659
LDO
12V
POSITIVE
SECONDARY
OUTPUT
A reasonable minimum value for h is 1.5, but this may
be adjusted up or down to allow tradeoffs between
OFF ( MIN ) × h
?
?
?
?
MAX1999
V SAG , output capacitance, and minimum operating
voltage. For a given value of h, the minimum operating
voltage can be calculated as:
V + ( MIN ) = ( V OUT _ + V DROP 1 ) + V DROP 2 ? V DROP 1
? t ?
1 ? ? ?
K
MAX1777
MAX1977
T1
10 μ H
1:2.2
DL_
T1 = TRANSPOWER TECHNOLOGIES TTI-5870
Figure 12. Transformer-Coupled Secondary Output
5V
MAIN
OUTPUT
28
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