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| 型号： | LT1766IGN#TR |
| 厂商： | Linear Technology |
| 文件页数： | 14/30页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.5A 16SSOP |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.2 V ~ 54 V |
| 输入电压： | 5.5 V ~ 60 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz |
| 电流 - 输出： | 1.5A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-SSOP |
| 其它名称： | LT1766IGNTR |
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LT1766/LT1766-5
APPLICATIONS INFORMATION
Discontinuous mode is entered when the output load
current is less than one-half of the inductor ripple current
(I LP-P ). In this mode, inductor current falls to zero before
the next switch turn on (see Figure 8). Buck converters
will be in discontinuous mode for output load current
given by:
Short-Circuit Considerations
The LT1766 is a current mode controller. It uses the V C
node voltage as an input to a current comparator which
turns off the output switch on a cycle-by-cycle basis as
this peak current is reached. The internal clamp on the V C
node, nominally 2V, then acts as an output switch peak
I OUT
Discontinuous Mode
<
( V OUT + V F )( V IN – V OUT – V F )
( 2 )( V IN )( f )( L )
current limit. This action becomes the switch current limit
speci?cation. The maximum available output power is then
determined by the switch current limit.
I OUT(MAX) I P 2
=
( 2 )( I LP-P )
( I P ) ( 2 ( f )( L )( V IN ) )
+ V )( V – V
f ? t ON ≤ F
The inductor value in a buck converter is usually chosen
large enough to keep inductor ripple current (I LP-P ) low;
this is done to minimize output ripple voltage and maximize
output load current. In the case of large inductor values,
as seen in the equation above, discontinuous mode will
be associated with light loads .
When choosing small inductor values, however, discon-
tinuous mode will occur at much higher output load cur-
rents. The limit to the smallest inductor value that can be
chosen is set by the LT1766 peak switch current (I P ) and
the maximum output load current required, given by:
Discontinuous Mode
=
2 ( V OUT F IN OUT – V F )
Example: For V IN = 15V, V OUT = 5V, V F = 0.63V, f = 200kHz
and L = 10μH.
A potential controllability problem could occur under
short-circuit conditions. If the power supply output is
short circuited, the feedback ampli?er responds to the
low output voltage by raising the control voltage, V C ,
to its peak current limit value. Ideally, the output switch
would be turned on, and then turned off as its current
exceeded the value indicated by V C . However, there is ?nite
response time involved in both the current comparator and
turn-off of the output switch. These result in a minimum
on-time, t ON(MIN) . When combined with the large ratio of
V IN to (V F + I ? R), the diode forward voltage plus inductor
I ? R voltage drop, the potential exists for a loss of control.
Expressed mathematically the requirement to maintain
control is:
V + I ? R
V IN
where:
f = Switching frequency
t ON = Switch minimum on-time
( 1 . 5 ) ? ( 200 ? 10 3 )( 10 – 5 )( 15 )
I OUT(MAX)
Discontinuous
Mode
=
2
2 ( 5 + 0 . 63 )( 15 – 5 – 0 . 63 )
V F = Diode forward voltage
V IN = Input voltage
I ? R = Inductor I ? R voltage drop
I OUT(MAX) = 0.639A
Discontinuous Mode
What has been shown here is that if high inductor ripple
current and discontinuous mode operation can be tolerated,
small inductor values can be used. If a higher output load
current is required, the inductor value must be increased.
If I OUT(MAX) no longer meets the discontinuous mode
criteria, use the I OUT(MAX) equation for continuous mode;
the LT1766 is designed to operate well in both modes of
operation, allowing a large range of inductor values to
be used.
14
If this condition is not observed, the current will not be
limited at I PK , but will cycle-by-cycle ratchet up to some
higher value. Using the nominal LT1766 clock frequency
of 200KHz, a V IN of 40V and a (V F + I ? R) of say 0.7V, the
maximum t ON to maintain control would be approximately
90ns, an unacceptably short time.
The solution to this dilemma is to slow down the oscil-
lator when the FB pin voltage is abnormally low thereby
indicating some sort of short-circuit condition. Oscillator
frequency is unaffected until FB voltage drops to about
2/3 of its normal value. Below this point the oscillator
1766fc
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1766IGN-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:5.5V to 60V 1.5A, 200kHz Step-Down Switching Regulator |
| LT1767 | 制造商:LINER 制造商全称:Linear Technology 功能描述:1.4A, 500kHz Step-Down Switching Regulator |
| LT1767-1.8 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators |
| LT1767-2.5 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators |
| LT1767-3.3 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators |
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