LTC3603 Linear Dimensions Semiconductor, LTC3603 Datasheet - Page 11

• Manufacturer Part Number: LTC3603
• Description: Monolithic Synchronous Step-Down Regulator
• Manufacturer: Linear Dimensions Semiconductor

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Burst Clamp Programming
If the voltage on the SYNC/MODE pin is less than INTV
by 1V or more, Burst Mode operation is enabled. During
Burst Mode operation, the voltage on the SYNC/MODE
pin determines the burst clamp level. This level sets the
minimum peak inductor current, I
cycle according to the following equation:
V
be programmed in the range of 0A to 3.5A, which cor-
responds to a V
load current drops, the peak inductor current decreases
to keep the output voltage in regulation. When the output
load current demands a peak inductor current that is less
than I
current to remain equal to I
reductions in the load current. Since the average inductor
current is therefore greater than the output load current,
the voltage on the ITH pin will decrease. When the I
voltage drops to 330mV, sleep mode is enabled in which
both power MOSFETs are shut off along with most of the
circuitry to minimize power consumption. All circuitry is
turned back on and the power MOSFETs begin switching
again when the output voltage drops out of regulation. The
value for I
output voltage ripple. As the value of I
sleep time between pulses and the output voltage ripple
increases. The burst clamp voltage, V
by a resistor divider from the INTV
the SYNC/MODE pin may be tied directly to the V
set V
divider resistor (R3) to set V
Figure 2).
APPLICATIONS INFORMATION
BURST
V
BURST
BURST
BURST
is the voltage on the SYNC/MODE pin. I
BURST
, the burst clamp will force the peak inductor
= 0.6V (I
=
I
BURST
6
BURST
A V
is determined by the desired amount of
/
BURST
+
range of 0.42V to 1V. As the output
0 42
.
= 1A), or through an additional
V
BURST
BURST
BURST
regardless of further
= 0.46V to 0.6V (see
CC
BURST
V
, for each switching
BURST
BURST
pin. Alternatively,
LTC3603
SYNC/MODE
Figure 2. Programing the Burst Clamp
= 0.46V TO 1V
increases, the
, can be set
INTV
SGND
BURST
CC
FB
pin to
can
CC
TH
R2
R1
Pulse-skipping, which is a compromise between low output
voltage ripple and effi ciency, can be implemented by con-
necting the SYNC/MODE pin to ground. This sets I
0A. In this condition, the peak inductor current is limited by
the minimum on-time of the current comparator and the
lowest output voltage ripple is achieved while still operating
discontinuously. During very light output loads, pulse-skip-
ping allows only a few switching cycles to be skipped while
maintaining the output voltage in regulation.
Frequency Synchronization
The LTC3603’s internal oscillator can be synchronized to
an external 5V clock signal. During synchronization, the
top MOSFET turn-on is locked to the falling edge of the
external frequency source. The synchronization frequency
range is 300kHz to 3MHz. Synchronization only occurs if
the external frequency is greater than the frequency set by
the R
by the oscillator’s internal ramp, the external frequency
should be set 25% higher than the frequency set by the
R
is present. When synchronized, the LTC3603 will operate
in pulse-skipping mode.
INTV
The LTC3603 features an integrated P-channel low dropout
linear regulator (LDO) that supplies power to the INTV
supply pin from the PV
designed to deliver up to 35mA of load current for the
powering of the internal gate drivers and other internal
circuitry. A small external load may also be applied provided
that the total current from the INTV
exceed 35mA. The INTV
no less than a 0.22μF ceramic capacitor. A 1μF ceramic
capacitor is suitable for most applications.
V
T
BURST
resistor to ensure that adequate slope compensation
LTC3603
CC
SYNC/MODE
T
= 0.46V TO 0.6V
resistor. Because slope compensation is generated
Regulator
SGND
3603 F02
FB
R3 (OPTIONAL)
R1
R2
IN
CC
pin. This LDO supply has been
V
pin should be bypassed with
OUT
CC
LTC3603
supply does not
BURST
11
3603f
CC
to