LTC1624CS8 Linear Technology, LTC1624CS8 Datasheet - Page 19

• Manufacturer Part Number: LTC1624CS8
• Description: IC SW REG CONTROLLER N-CH 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost), Inverting, Sepicr

Specifications of LTC1624CS8

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 30 V
• Current - Output: 2A
• Frequency - Switching: 200kHz
• Voltage - Input: 3.5 ~ 36 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS
constant inversely related to the gate drive current. The
maximum switch current occurs at V
switch current is I
across the switch is V
MOSFETs have I
includes an additional term for transition losses that are
highest at high total input plus output voltages. For
( V
improves with larger MOSFETs, while for ( V
> 20V the transition losses rapidly increase to the point
that the use of a higher R
actual provides higher efficiency. For additional informa-
tion refer to the Step-Down Converter: Power MOSFET
Selection in the Applications Information section.
Positive-to-Negative Converter: Inductor Selection
For most applications the inductor will fall in the range of
10 H to 100 H. Higher values reduce the input and output
ripple voltage (although not as much as step-down con-
verters) and also reduce core loss. Lower inductor values
are chosen to reduce physical size and improve transient
response but do increase output ripple.
Like the boost converter, the input current of the positive-
to-negative converter is calculated at full load current.
Peak inductor current can be significantly higher than
output current, especially with smaller inductors (with
high I
ous mode operation and calculates maximum peak induc-
tor current at minimum V
The ripple current in the inductor ( I
50% of the peak inductor current occuring at V
I
at minimum V
where
OUT(MAX)
is the temperature dependency of R
I
L PEAK
OUT
L
I
values). The following formula assumes continu-
SW MAX
+ V
to minimize output ripple. Maximum I
IN
I
) < 20V the high current efficiency generally
OUT MAX
IN
.
SW(MAX)
2
R losses plus the P
U
I
OUT MAX
IN(MAX)
INFORMATION
V
IN
U
+ I
DS(ON)
IN
:
+ V
L
/2. The maximum voltage
V
V
OUT
V
device with lower C
IN
IN
OUT
W
L
IN(MIN)
) is typically 20% to
V
V
DS(ON)
OUT
.
IN
V
MAIN
D
and the peak
OUT
IN(MIN)
V
and k is a
U
D
equation
L
2
I
occurs
L
+ V
and
RSS
IN
)
Specify the maximum inductor current to safely handle
I
ing (current when inductance begins to fall) exceeds the
maximum current rating set by R
Positive-to-Negative Converter: R
Maximum Output Current
R
Remember the LTC1624 current comparator has a maxi-
mum threshold of 160mV/R
tor threshold sets the peak of the inductor current, yielding
a maximum average output current I
I
remainder divided by the duty cycle.
Allowing a margin for variations in the LTC1624 (without
considering variation in R
current in the inductor, yields:
Positive-to-Negative Converter: Output Diode
The output diode conducts current only during the switch
off-time. Peak reverse voltage for positive-to-negative
converters is equal to V
current in normal operation is equal to I
Peak diode current (occurring at V
Positive-to-Negative Converter: Input and
Output Capacitors
The output capacitor is normally chosen by its effective
series resistance (ESR), because this is what determines
output ripple voltage. Both input and output capacitors
need to be sized to handle the ripple current safely.
L(PEAK)
L(PEAK)
SENSE
I
R
D PEAK
SENSE
I
L
P-P
. Make sure the inductor’s saturation current rat-
is chosen based on the required output current.
less half the peak-to-peak ripple current with the
I
I
OUT MAX
OUT MAX
200
100
kHz L V
mV
V
IN
SENSE
V
V
V
IN MIN
OUT
OUT
OUT
SENSE
IN
V
) and assuming 30% ripple
IN
+ V
V
V
SENSE
. The current compara-
IN MIN
OUT
V
IN(MIN)
V
SENSE
D
IN
D
V
. Average forward
OUT
OUT(MAX)
.
D(PEAK)
1
V
Selection for
LTC1624
) is:
D
V
D
2
I
L
equal to
– I
19
L
/2.