LTC1142(RevC) 查看數據表（PDF） - Linear Technology
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LTC1142 Datasheet PDF : 20 Pages
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APPLICATIO S I FOR ATIO
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
LTC1142/LTC1142L/LTC1142HV
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 APPLICATIONS N
VIN
5.2V TO 18V
VOUT1
3.6V/2A
COUT1
220µF
10V
×2
RSENSE1
0.05Ω
CIN1
22µF
35V
×2
L1
25µH
R2
100k
1%
R1
52.3k
1%
D1
MBRS130T3
100pF
0.22µF
P-CH
24
Si9430DY
23
VIN1
PDRIVE 1
0V = NORMAL
>1.5V = SHUTDOWN
3
17
SHUTDOWN 1
SHUTDOWN 2
0.22µF
10
VIN2 9
PDRIVE 2
P-CH
Si9430DY
1000pF
N-CH
Si9410DY
1 SENSE+1
SENSE –1
28
2 VFB1
NDRIVE 1
6
PGND1 SGND1 CT1
5
4 25
SENSE+2 15
LTC1142HV-ADJ
SENSE –2
14
VFB2 16
NDRIVE 2
20
ITH1 ITH2 CT2 SGND2 PGND2
27
13 11
18 19
RC1 RC2
1k
1k
1000pF
N-CH
Si9410DY
CT1 CC1 CC2 CT2
270pF 3300pF 3300pF 270pF
+
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%
RSENSE1, RSENSE2 : KRL SL-1/2-R050J
L1: COILTRONICS CTX25-4
L2: COILTRONICS CTX33-5
1142 F11
Figure 11. LTC1142HV-ADJ Dual Regulator with 3.6V/2A and 5V/2A Outputs
17
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