LTC3788IGN-1#PBF Linear Technology, LTC3788IGN-1#PBF Datasheet - Page 18

• Manufacturer Part Number: LTC3788IGN-1#PBF
• Description: IC CTLR BOOST 2PH DUAL 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LTC3788IGN-1#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Adj to 60V
• Current - Output: 25A
• Frequency - Switching: 105kHz ~ 760kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC3788-1
APPLICATIONS INFORMATION
output capacitor depend on the duty cycle, the number
of phases and the maximum output current. Figure 3 il-
lustrates the normalized output capacitor ripple current
as a function of duty cycle in a 2-phase confi guration. To
choose a ripple current rating for the output capacitor,
fi rst establish the duty cycle range based on the output
voltage and range of input voltage. Referring to Figure 3,
choose the worst-case high normalized ripple current as
a percentage of the maximum load current.
Multiple capacitors placed in parallel may be needed to
meet the ESR and RMS current handling requirements.
Dry tantalum, special polymer, aluminum electrolytic and
ceramic capacitors are all available in surface mount
packages. Ceramic capacitors have excellent low ESR
characteristics but can have a high voltage coeffi cient.
Capacitors are now available with low ESR and high ripple
current ratings (i.e., OS-CON and POSCAP).
Setting Output Voltage
The LTC3788-1 output voltages are each set by an exter-
nal feedback resistor divider carefully placed across the
output, as shown in Figure 4. The regulated output voltage
is determined by:
Great care should be taken to route the V
noise sources, such as the inductor or the SW line.
18
V
OUT
Figure 3. Normalized Output Capacitor Ripple
Current (RMS) for a Boost Converter
=
3.25
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
1 2
0
0.1
.
V
0.2
⎛
⎜
⎝
1
DUTY CYCLE OR (1-V
0.3
+
R
R
0.4
B
A
⎞
⎟
⎠
1-PHASE
0.5
0.6
IN
/V
2-PHASE
0.7
OUT
)
0.8
FB
37881 F03
0.9
line away from
Soft-Start (SS Pins)
The start-up of each V
the respective SS pins. When the voltage on the SS pin
is less than the internal 1.2V reference, the LTC3788-1
regulates the VFB pin voltage to the voltage on the SS
pin instead of 1.2V.
Soft-start is enabled by simply connecting a capacitor from
the SS pin to ground, as shown in Figure 5. An internal
10μA current source charges the capacitor, providing a
linear ramping voltage at the SS pin. The LTC3788-1 will
regulate the VFB pin (and hence, V
voltage on the SS pin, allowing V
from V
time will be approximately:
INTV
The LTC3788-1 features two separate internal P-channel
low dropout linear regulators (LDO) that supply power at
the INTV
EXTV
pin. INTV
LTC3788-1’s internal circuitry. The VBIAS LDO and the
EXTV
supply a peak current of 50mA and must be bypassed to
ground with a minimum of 4.7μF ceramic capacitor. Good
t
SS
CC
CC
CC
IN
Figure 5. Using the SS Pin to Program Soft-Start
=
Regulators
pin depending on the connection of the EXTV
LDO regulate INTV
CC
C
to its fi nal regulated value. The total soft-start
CC
SS
pin from either the VBIAS supply pin or the
powers the gate drivers and much of the
Figure 4. Setting Output Voltage
•
10
. 1 2
µA
LTC3788-1
V
C
SS
OUT
VFB
is controlled by the voltage on
SS
SGND
CC
LTC3788-1
to 5.4V. Each of these can
37881 F05
V
OUT
OUT
OUT
R
R
37881 F04
B
A
) according to the
to rise smoothly
37881fa
CC