LTC1142-ADJ Linear Technology, LTC1142-ADJ Datasheet - Page 17

• Manufacturer Part Number: LTC1142-ADJ
• Description: Dual High Efficiency Synchronous Step-Down Switching Regulators
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
3.6V/2A
TYPICAL APPLICATIONS
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 (I
applications when they are lightly loaded.
An external offset is put in series with the Sense
subtract from the built-in 25mV offset. An example of this
technique is shown in Figure 10. Two 100 resistors are
inserted in series with the sense leads from the sense
resistor.
V
C
220 F
OUT1
OUT1
10V
2
[PIN 28(14)]
[PIN 1(15)]
+
Figure 10. Suppression of Burst Mode Operation
52.3k
100k
SENSE
SENSE
R
1%
1%
0.05
R2
R1
SENSE1
+
–
+
MBRS130T3
100pF
C
22 F
35V
25 H
IN1
L1
R3
2
R
L1: COILTRONICS CTX25-4
L2: COILTRONICS CTX33-5
U U
SENSE1,
1000pF
D1
R
SENSE2
N-CH
Si9410DY
1000pF
100
100
P-CH
Si9430DY
Figure 11. LTC1142HV-ADJ Dual Regulator with 3.6V/2A and 5V/2A Outputs
R2
R1
: KRL SL-1/2-R050J
0.22 F
U
23
28
W
1
2
6
SENSE
PDRIVE 1
SENSE
NDRIVE 1
PGND1 SGND1 C
V
N
V
FB1
IN1
5
24
+
+
–
1
1
R
SENSE
1142 F10
C
OUT
SHUTDOWN 1
4
OUT
V
U
OUT
–
T1
> 5A)
25
pin to
3
C
270pF
T1
>1.5V = SHUTDOWN
0V = NORMAL
LTC1142HV-ADJ
I
5.2V TO 18V
TH1
27
C
3300pF
R
1k
C1
V
C1
IN
I
TH2
13
C
3300pF
With the addition of R3 a current is generated through R1
causing an offset of:
If V
Burst Mode operation is prevented from occurring. Since
V
decreased by the same offset. Thus, to get back to the
same I
To prevent noise spikes from erroneously tripping the
current comparator, a 1000pF capacitor is needed across
Pins 1 (15) and Pins 28 (14).
R
SHUTDOWN 2
R
1k
C2
LTC1142/LTC1142L/LTC1142HV
C2
OFFSET
SENSE
V
OFFSET
C
T2
OFFSET
11
17
C
270pF
T2
MAX
SGND2 PGND2
is constant, the maximum load current is also
> 25mV, the built-in offset will be cancelled and
18
75
, the value of the sense resistor must be lower:
I
NDRIVE 2
PDRIVE 2
SENSE
SENSE
MAX
mV
V
V
IN2
V
OUT
19
10
FB2
+
–
2
2
15
14
9
16
20
0.22 F
Si9430DY
Si9410DY
R
1000pF
N-CH
1
P-CH
R
1
R
3
D2
MBRS130T3
33 H
L2
100pF
+
C
22 F
35V
R
0.05
IN2
SENSE2
2
R3
49.9k
1%
R4
150k
1%
+
17
C
220 F
10V
1142 F11
V
5V/2A
OUT2
2
OUT2