LTC3704EMS Linear Technology, LTC3704EMS Datasheet - Page 20

• Manufacturer Part Number: LTC3704EMS
• Description: IC INV SYNC 5.2V 50MA 10MSOP
• Manufacturer: Linear Technology
• Type: Invertingr

Specifications of LTC3704EMS

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -5.2V
• Current - Output: 50mA
• Frequency - Switching: 50kHz ~ 1MHz
• Voltage - Input: 2.5 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
LTC3704
regulator feedback loop acts on the resulting error amp
output signal to return V
this recovery time, V
ringing that would indicate a stability problem.
A second, more severe transient can occur when connect-
ing loads with large (> 1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C
regulator can deliver enough current to prevent this prob-
lem if the load switch resistance is low and it is driven
quickly. The only solution is to limit the rise time of the
switch drive in order to limit the inrush current di/dt to the
load.
Design Example: A 5V to 15V Input, –5V at 2A Output
Positive-to-Negative Converter
The design example presented here will be for the circuit
shown in Figure 1. The input voltage range is 5V to 15V,
and the output is -5V. The maximum load current is 2A at
an input voltage of 5V (3A peak), and 3A at an input voltage
of 15V (5A peak).
1. The maximum duty cycle of the main switch is:
2. Pulse-Skip operation is chosen, so the MODE/SYNC pin
is connected to the INTV
3. The operating frequency is chosen to be 300kHz to
reduce the size of the inductors. From Figure 5, the resistor
from the FREQ pin to ground is 80.6k.
4. A total inductor ripple current of 40% of the maximum
is chosen, so the inductor ripple current is:
For a standard 1:1 coupled inductor, the inductance is
therefore:
20
D
Δ
Δ
MAX
I
I
L
L
O
1
1
, causing a nearly instantaneous drop in V
= −
=
=
0 4 2 0
. • . •
V
χ •
OUT
I
O MAX
(
V
−
OUT
U
V
1 0 5
O
IN MIN
)
– .
0 5
can be monitored for overshoot or
(
•
.
O
1
CC
U
to its steady-state value. During
–
D
)
pin.
MAX
D
=
=
MAX
0 8
–
.
–
10
5
A
W
=
50
%
U
O
. No
The minimum saturation current for this inductor is:
The inductor chosen is a BH Electronics part # 510-1009,
which has an open circuit parallel inductance of 4.56μH
and a maximum dc current rating of 6.5A.
5. For the power MOSFET,
At the maximum duty cycle of 50%, the maximum SENSE
pin voltage is reduced to 130mV due to slope compensa-
tion, as shown in Figure 11. Assuming a maximum
junction temperature of 125°C for the power MOSFET,
ρ
The MOSFET chosen was Siliconix/Vishay’s Si4884, which
has a maximum R
The minimum BV
is Q
6. The output diode must withstand a reverse voltage of
V
I
current in the diode is:
The power dissipated in this diode at full load is:
O(MAX)
Τ
IN(MAX)
I
R
R
I
L
= 1.5, and
LSAT MIN
D PEAK
G
1
DS ON
DS ON
(
=
= 20nC.
(
(
= 5.0A (peak output current at V
L
(
2
– V
)
)
)
=
=
=
≤
≤
)
2
2 0 8 300
≥
=
V
0 130
⎛
⎜
⎝
V
O
•
1
SENSE MAX
.
• . •
IN MIN
–
1 2 2 0
Δ
+
= 20V and a continuous current of
DSS
(
. • . •
⎛
⎜
⎝
DS(ON)
I
L
1
χ
2
5
1
+
•
⎞
⎟
⎠
(
= 30V and the maximum gate charge
•
)
– . • . • .
•
χ
f
2
1 2 2 0 1 5
I
•
O MAX
⎞
⎟
⎠
= 16.5mΩ at V
D
(
k
)
0 5 1
•
1 0 5
MAX
•
I
. –
• .
– .
O MAX
⎛
⎜
⎝
0 5 5 2
1
(
1
)
+
=
=
χ
2
=
)
6
D
•
⎞
⎟
⎠
A
4 8
.
1
MAX
•
.
=
μ
–
I
O MAX
IN
A
18 1
GS
H
D
(
1
= 15V). The peak
–
MAX
.
= 4.5V at 25°C.
1
m
)
Ω
•
ρ
Τ
3704fb