参数资料
| 型号： | LTC3444EDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/20页 |
| 文件大小： | 0K |
| 描述： | IC DC/DC CONV WCDMA 8-DFN |
| 标准包装： | 2,500 |
| 应用： | 转换器，WCDMA 功率放大器应用 |
| 输入电压： | 2.75 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | 0.5 V ~ 5 V |
| 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 |
| 供应商设备封装： | 8-DFN-EP（3x3） |
| 包装： | 带卷 (TR) |
LTC3444
OPERATIO
Optional Schottky Diodes
Schottky diodes across the synchronous switches B and
A troublesome problem when operating in boost mode is
dealing with the right-half plane zero (RHP), given by:
D are not required, but provide a lower drop during the
break-before-make time (typically 15ns) of the NMOS to
PMOS transition, improving efficiency. Use a surface
f RHPZ =
V IN 2
2 ? π ? I OUT ? L ? V OUT
Hz
mount Schottky diode such as an MBRM120T3 or equiva-
lent. Do not use ordinary rectifier diodes, since the slow
recovery times will compromise efficiency.
Closing the Feedback Loop
The LTC3444 incorporates voltage mode PWM control.
The control to output gain varies with operation region
(buck, boost, buck-boost), but is usually ~20dB. The
output filter exhibits a double pole response, as given by:
The RHP zero has a +20dB/dec gain typical of a zero but
the –90 ° phase lag of a pole. This causes the loop gain to
flatten out while the phase margin decreases. The only way
to combat a RHP zero is to roll off the loop well before the
RHP zero frequency.
LOOP COMPENSATION NETWORKS
A simple Type I compensation network, refer to Figure 7,
can be incorporated to stabilize the loop, but at a cost of
f FILTER _ POLE =
( in buck mod e )
1
2 ? π ? L ? C OUT
Hz
reduced bandwidth and slower transient response. To
ensure proper phase margin using Type I compensation,
the loop must be crossed over at least a decade before the
output LC double pole frequency. The unity-gain fre-
quency of the error amplifier with the Type I compensation
f FILTER _ POLE =
V IN
2 ? V OUT ? π ? L ? C OUT
( in boost mod e )
Hz
is given by:
f UG =
1
2 ? π ? R 1 ? C 2
Hz
where L is in Henries and C OUT is in farads.
The output filter zero is given by:
WCDMA applications demand an improved transient re-
sponse to the input control voltage. In other applications,
the output capacitor can be increased to meet help meet
f FILTER _ ZERO =
1
2 ? π ? R ESR ? C OUT
Hz
the load transient requirements.
where R ESR is the equivalent series resistance of the
output cap.
C2
7
V C
FB
8
V REF
R2
R1
V OUT
3444 F07
Figure 7. Error Amplifier with Type I Compensation
3444fb
16
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