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参数资料
| 型号： | SC4503WLTRT |
| 厂商： | Semtech |
| 文件页数： | 10/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 1.4A 8MLPD |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 27V |
| 输入电压： | 2.5 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.3MHz |
| 电流 - 输出： | 1.4A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-WFDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-MLPD（2x2） |
| 其它名称： | SC4503WLDKR |
SC4503
POWER MANAGEMENT
Applications Information (Cont.)
lessen jittery tendency but not so steep that large ? ux swing
=
?
?
?
(5)
Assuming that the voltage of a nearly discharged Li-ion cell
is 2.6V. Using V D =0.5V, V CESAT =0.3V and D=0.86 in (5),
decreases ef ? ciency. For continuous-conduction mode
operation, inductor ripple current Δ I L between 0.35A and
0.6A is a good compromise. Setting Δ I L = 0.43A, V D = 0.5V
and f = 1.3MHz in (7),
<
?
?
?
?
=
=
?
?
+
=
?
+
(8)
where L is in μ H.
Transient headroom requirement further reduces the maxi-
) . If V varies over a wide range, then
( +
mumachievableoutputvoltagetobelow16V.
Minimum Controllable On-Time
The operating duty cycle of a boost converter decreases as
V IN approaches V OUT . Sensed switch current ramp modulates
the pulse width in a current-mode switching regulator. This
current ramp is absent unless the switch is turned on. The
intersection of this ramp with the error ampli ? er output
determines the switch on-time. The propagation delay
time required to immediately turn off the switch after it is
turned on is the minimum controllable on time. Measured
minimum on time of the SC4503 is load-dependent and
ranges from 180ns to 220ns at room temperature. The
switch in the SC4503 is either not turned on, or, for at least
this minimum. If the regulator requires a switch on-time
less than this controllable minimum, then it will either skip
cycles or start to jitter.
Equation (7) shows that for a given V OUT , Δ I L is the highest
when = IN
choose L based on the nominal input voltage.
The saturation current of the inductor should be 20-30%
higher than the peak current limit (1.9 A). Low-cost powder
iron cores are not suitable for high-frequency switching
power supplies due to their high core losses. Inductors
with ferrite cores should be used.
Discontinuous-Conduction Mode
The output-to-input voltage conversion ratio = in
continuous-conduction mode is limited by the maximum
duty cycle D MAX :
Inductor Selection
<
?
=
?
=
( ? )
duction mode (DCM). De ? ne R = OUT as the equivalent
TheinductorripplecurrentΔI L ofaboostconverterincon-
tinuous-conduction mode is
? = (6)
where f is the switching frequency and L is the induc-
tance.
Higher voltage conversion ratios can be achieved by oper-
ating the boost converter in full-time discontinuous-con-
V
I OUT
output load resistance. The following inequalities must be
satis ? ed for DCM operation:
Substituting (3) into (6) and neglecting V CESAT ,
<
?
(9)
? =
?
+
(7)
and,
In current-mode control, the slope of the modulating
(sensed switch current) ramp should be steep enough to
? 2007 Semtech Corp.
10
=
<
(10)
www.semtech.com
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