LT1956IGN#TRPBF Linear Technology, LT1956IGN#TRPBF Datasheet - Page 24

• Manufacturer Part Number: LT1956IGN#TRPBF
• Description: IC SW REG STP-DWN HI VOLT 16SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1956IGN#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 45 V
• Current - Output: 1.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 5.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LT1956/LT1956-5
APPLICATIO S I FOR ATIO
couples energy to L2 and ensures equal voltages across
L2 and L1 during steady state. Instead of using a trans-
former for L1 and L2, uncoupled inductors were used
because they require less height than a single transformer,
can be placed separately in the circuit layout for optimized
space savings and reduce overall cost. This is true even
when the uncoupled inductors are sized (twice the value of
inductance of the transformer) in order to keep ripple
current comparable to the transformer solution. If a single
24
300
500
450
400
350
250
200
150
100
50
0
Figure 14b. V
Allowable Load Current vs V
(5V) Load Current
0
V
200
OUT1
LOAD CURRENT (mA)
OUT2
400
U
(–5V) Maximum
(TRANSIENTS
9V TO 12V
U
TO 36V)
600
CERAMIC
GND
V
OUT1
IN
**SEE FIGURE 14c FOR V
2.2 F
50V
*SUMIDA CDRH4D28-150
†
1956 F15b
LOAD CURRENT RELATIONSHIP
IF LOAD CAN GO TO ZERO, AN OPTIONAL
PRELOAD OF 500 CAN BE
USED TO IMPROVE REGULATION
C3
800
W
Figure 14a. Dual Polarity Output Converter
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
4.75
V
SHDN
SYNC
IN
GND
0
U
OUT1
Figure 14c. V
Voltage vs Load Current
LT1956
BOOST
V
750mA
R
2.2k
, V
100
OUT1
C
C
3300pF
OUT2
C
V
OUT2
LOAD CURRENT
V
500mA
200
OUT1
V
LOAD CURRENT (mA)
SW
C
FB
10 F
6.3V
C
220pF
CER
0.1 F
LOAD CURRENT
OUT2
F
C4
300
C2
V
250mA
transformer becomes available to provide a better height/
cost solution, refer to the dual output SEPIC circuit de-
scription in Design Note 100 for correct transformer
connection.
During switch on-time, in steady state, the voltage across
both L1 and L2 is positive and equal; with energy (and
current) ramping up in each inductor. The current in L2 is
provided by the coupling capacitor C4. During switch off-
time, current ramps downward in each inductor. The
OUT1
+
(–5V) Output
400
LOAD CURRENT
B0540W
L2*
MMSD914TI
D1
B0540W
D3
500
15 H
D2
L1*
1956 F14c
15.4k
4.99k
R2
R1
600
6.3V CER
10 F
C6
+
+
100
C5
10 F
6.3V
CER
90
80
70
60
50
40
30
20
10
0
0
Figure 14d. Dual Polarity Output
Converter Efficiency
V
1956 F14a
OUT1
V
5V
V
–5V
OUT1
OUT2
100
LOAD CURRENT
V
250mA
**
**
OUT2
V
†
OUT1
LOAD CURRENT (mA)
200
LOAD CURRENT
750mA
300
400
1956 F14d
1956f
500