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参数资料
| 型号： | LTC3812IFE-5#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, PDSO16 |
| 封装： | 4.40 MM, PLASTIC, TSSOP-16 |
| 文件页数： | 18/32页 |
| 文件大小： | 425K |
| 代理商： | LTC3812IFE-5#TR |
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LTC3812-5
25
38125fb
where H(s) was given in equation 2 and A(s) depends on
compensation circuit used:
Type 2:
A (s)
=
1
+ sR3 C2
s RFB1 C2 + C3
()1+sR3
C2 C3
C2
+ C3
Type 3:
A (s)
=
1
s R1 C2
+ C3
(
)
1
+ s R1+R3
()C3
()1+sR2C1
()
1
+ sR3 C3
()1+sR2
C1 C2
C1
+ C2
For SPICE, replace VSTIM line in the previous PSPICE
code with following code and generate a gain/phase plot
of V(out)/V(outin):
rfb1 outin vfb 52.5k
rfb2 vfb 0 10k
eithx ithx 0 laplace {0.8-v(vfb)} =
{1/(1+s/1000)}
eith ith 0 value={limit(1e6*v(ithx),0,2.4)}
cc1 ith vfb 4p
cc2 ith x1 8p
rc x1 vfb 210k
rf outin x2 11k ;delete this line for Type 2
cf x2 vfb 120p ;delete this line for Type 2
vstim out outin dc=0 ac=1m
PULSE SKIP MODE OPERATION AND FCB PIN
The FCB pin determines whether the bottom MOSFET
remains on when current reverses in the inductor. Tying
this pin above its 0.8V threshold enables pulse skip mode
operation where the bottom MOSFET turns off when in-
ductor current reverses. The load current at which current
reverses and discontinuous operation begins depends on
the amplitude of the inductor ripple current and will vary
with changes in VIN. Tying the FCB pin below the 0.8V
threshold forces continuous synchronous operation, al-
lowing current to reverse at light loads and maintaining
high frequency operation. To prevent forcing current back
into the main power supply, potentially boosting the input
supply to a dangerous voltage level, forced continuous
mode of operation is disabled when the RUN/SS voltage
is below 2.5V during soft-start or tracking. During these
two periods, the PGOOD signal is forced low.
In addition to providing a logic input to force continuous
operation, the FCB pin provides a mean to maintain a yback
winding output when the primary is operating in pulse
skip mode. The secondary output VOUT2 is normally set as
shown in Figure 13 by the turns ratio N of the transformer.
However, if the controller goes into pulse skip mode and
halts switching due to a light primary load current, then
VOUT2 will droop. An external resistor divider from VOUT2
to the FCB pin sets a minimum voltage VOUT2(MIN) below
which continuous operation is forced until VOUT2 has risen
above its minimum.
VOUT2(MIN) = 0.8V 1+
R4
R3
Table 1
FCB PIN
CONDITION
DC Voltage: 0V to 0.75V
Forced Continuous
Current Reversal Enabled
DC Voltage: ≥0.85V
Pulse Skip Mode Operation
No Current Reversal
Feedback Resistors
Regulating a Secondary Winding
APPLICATIONS INFORMATION
Figure 13. Secondary Output Loop
VIN
LTC3812-5
SGND
FCB
TG
SW
R3
R4
38125 F13
T1
1:N
BG
PGND
+
COUT2
1μF
R3
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