LT1312 Linear Technology, LT1312 Datasheet - Page 7

• Manufacturer Part Number: LT1312
• Description: Single PCMCIA VPP Driver/Regulator
• Manufacturer: Linear Technology

loaded without regard to the loading on the 5V output of
the LTC1142HV.
Continuous mode operation is only invoked when the
LT1312 is programmed to 12V. If the LT1312 is pro-
grammed to 0V, 3.3V or 5V, power is obtained directly
from the main power source (battery pack) through diode
D1. Again, the LT1312 output can be loaded without
regard to the loading of the main 5V output.
R4 and C4 absorb transient voltage spikes associated with
the leakage inductance inherent in T1's secondary winding
and ensure that the auxiliary supply does not exceed 20V.
Figure 2 is a graph of output voltage versus output current
for the auxiliary 14V supply shown in Figure 1. Note that
the auxiliary supply voltage is slightly higher when the 5V
output is heavily loaded. This is due to the increased
energy flowing through the main 5V inductor.
LTC1142 Auxiliary Power from the 3.3V Output
The circuit of Figure 1 can be modified for operation with
low-battery count applications (6 cell). As the input volt-
age falls, the 5V duty cycle increases to the point where
APPLICATIONS
1/2 LTC1142HV
VALID
5V REG
EN0
EN1
SENSE
PDRIVE
NDRIVE
SENSE
V
IN
–
U
Figure 1. Deriving 14V Power from an Auxiliary Winding on the LTC1142HV 5V Regulator
10
9
20
15
14
6.5V TO 18V
INFORMATION
U
V
IN
Q2
Q1
R3
18k
Q3
VN7002
C2
1000pF
*LPE-6562-A026 DALE [phone]
D3
MBRS130T3
W
100
100
R1
R2
+
+
C1
68µF
R5
0.033
C3
220µF
U
MBRS140
T1
1.8T
30µH*
D1
22
R4
MBRS140
D2
1000pF
C4
there is simply not enough time to transfer energy from the
5V primary to the auxiliary winding. For applications
where heavy 12V load currents exist in conjunction with
low input voltages (<6.5V), the auxiliary winding can be
derived from the 3.3V section instead of the 5V section of
the LTC1142. In this case, a transformer with a turns ratio
of 1:3.4 to 1:3.6 should be used in place of the 3.3V section
+
C5
22µF
5V
OUTPUT
14V AUXILIARY SUPPLY
Figure 2. LTC1142 Auxiliary Supply Voltage
17
16
15
14
13
12
11
0.1
V
EN0 = HI
IN
I
OUT5V
= 8V
AUXILIARY OUTPUT CURRENT (mA)
1
= 0mA
VALID
EN0
EN1
LT1312
I
OUT5V
GND
V
S
10
VPP
SENSE
= 1A
OUT
CARD V
0V, 3.3V, 5V, 12V OR HI-Z
FROM
100
TO CARD VPP PIN
CC
LT1312 F2
PIN
+
LT1312 F1
1000
LT1312
1µF
7