LTC1142 查看數據表（PDF） - Linear Technology
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LTC1142 Datasheet PDF : 20 Pages
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LTC1142/LTC1142L/LTC1142HV
APPLICATIO S I FOR ATIO
may be loaded without regard to the primary output load,
providing that the loop remains in continuous mode
operation.
Burst Mode operation can be suppressed at low output
currents with a simple external network which cancels the
25mV minimum current comparator threshold. This tech-
nique is also useful for eliminating audible noise from
certain types of inductors in high current (IOUT > 5A)
applications when they are lightly loaded.
An external offset is put in series with the Sense – pin to
subtract from the built-in 25mV offset. An example of this
technique is shown in Figure 10. Two 100Ω resistors are
inserted in series with the sense leads from the sense
resistor.
SENSE +
[PIN 1(15)]
SENSE –
[PIN 28(14)]
R2
100Ω
1000pF
R1
100Ω
R3
RSENSE
VOUT
+
COUT
1142 F10
Figure 10. Suppression of Burst Mode Operation
With the addition of R3 a current is generated through R1
causing an offset of:
VOFFSET
=
VOUT
•
R1
R1+ R3
If VOFFSET > 25mV, the built-in offset will be cancelled and
Burst Mode operation is prevented from occurring. Since
VOFFSET is constant, the maximum load current is also
decreased by the same offset. Thus, to get back to the
same IMAX, the value of the sense resistor must be lower:
RSENSE
≈
75mV
IMAX
To prevent noise spikes from erroneously tripping the
current comparator, a 1000pF capacitor is needed across
Pins 1 (15) and Pins 28 (14).
TYPICAL APPLICATIO S (For additional high efficiency circuits, see Application Note 54)
VIN
5.2V TO 18V
VOUT1
3.6V/2A
COUT1
220µF
10V
×2
RSENSE1
0.05Ω
R2
100k
1%
R1
52.3k
1%
CIN1
22µF
35V
×2
L1
27µH
0.22µF
P-CH
24
Si9430DY
23
VIN1
PDRIVE 1
0V = NORMAL
>1.5V = SHDN
3
SHDN1
17
SHDN2
0.22µF
10
VIN2 9
PDRIVE 2
P-CH
Si9430DY
D1
MBRS130T3
1000pF
N-CH
Si9410DY
1 SENSE+1
SENSE+2 15
SENSE –1
28
2 VFB1
LTC1142HV-ADJ
SENSE –2
14
VFB2 16
NDRIVE 1
6
NDRIVE 2
20
PGND1 SGND1 CT1 ITH1 ITH2 CT2 SGND2 PGND2
5
4
25 27
13 11
18 19
RC1 RC2
1k
1k
1000pF
N-CH
Si9410DY
100pF
CT1 CC1
CC2
CT2
270pF 3300pF 3300pF 270pF
RSENSE1, RSENSE2 : DALE WSL-2010-.05
L1: SUMIDA CDRH125-270
L2: SUMIDA CDRH125-330
+
CIN2
22µF
35V
×2
L2
33µH
RSENSE2
0.05Ω
VOUT2
5V/2A
D2
MBRS130T3
100pF
+
R4
150k
1%
COUT2
220µF
10V
×2
R3
49.9k
1%
1142 F11
Figure 11. LTC1142HV-ADJ Dual Regulator with 3.6V/2A and 5V/2A Outputs
17
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