lt3493edcb-3 Linear Technology Corporation, lt3493edcb-3 Datasheet - Page 8

• Manufacturer Part Number: lt3493edcb-3
• Description: 1.2a, 750khz Step-down Switching Regulator In 2mm X 3mm Dfn
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT3493-3
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1%
resistors according to:
R2 should be 20k or less to avoid bias current errors.
Reference designators refer to the Block Diagram.
An optional phase lead capacitor of 22pF between V
and FB reduces light-load output ripple.
Input Voltage Range
The input voltage range for LT3493-3 applications de-
pends on the output voltage and on the absolute maximum
ratings of the V
The minimum input voltage is determined by either the
LT3493-3’s minimum operating voltage of 6.8V, or by its
maximum duty cycle. The duty cycle is the fraction of time
that the internal switch is on and is determined by the input
and output voltages:
where V
(~0.4V) and V
(~0.4V at maximum load). This leads to a minimum input
voltage of:
with DC
8
R
DC
V
IN MIN
1
=
(
=
MAX
R
D
V
2
IN
is the forward voltage drop of the catch diode
)
⎛
⎝ ⎜
V
=
= 0.91 (0.88 over temperature).
0 78
OUT
–
V
SW
.
V
OUT
V
IN
OUT
DC
SW
is the voltage drop of the internal switch
+
V
and BOOST pins.
MAX
V
U
+
+
–
D
V
1
V
⎞
⎠ ⎟
D
D
–
U
V
D
+
V
SW
W
U
OUT
The maximum input voltage is determined by the absolute
maximum ratings of the V
stant-frequency operation, the maximum input voltage is
determined by the minimum duty cycle, DC
the duty cycle requirement is less than DC
enter pulse-skipping mode. The onset of pulse-skipping
occurs at:
In pulse-skipping mode, the part skips pulses to control
the inductor current and regulate the output voltage,
possibly producing a spectrum of frequencies below
750kHz.
Note that this is a restriction on the operating input voltage
to remain in constant-frequency operation; the circuit will
tolerate transient inputs up to the absolute maximum
ratings of the V
regulation. The input voltage should be limited to V
during overload conditions (short-circuit or start-up).
AC COUPLED
V
200mV/DIV
IN PS
0.5A/DIV
20V/DIV
(
V
V
OUT
)
SW
I
L
=
C
V
V
I
L = 10µH
LOAD
OUT
OUT
IN
V
= 30V
OUT
DC
= 10µF
= 3V
IN
= 0.75A
and BOOST pins when the output is in
MIN
+
V
D
Figure 1
–
IN
2µs/DIV
V
D
and BOOST pins. For con-
+
V
SW
MIN
3493-3 F01
MIN
, the part will
= 0.10. If
IN(PS)
3493-3f