ltc3447edd-trpbf Linear Technology Corporation, ltc3447edd-trpbf Datasheet - Page 8

• Manufacturer Part Number: ltc3447edd-trpbf
• Description: I2c Controllable Buck Regulator In 3mm ? 3mm Dfn
• Manufacturer: Linear Technology Corporation

LTC3447
OPERATIO
the user should calculate the power dissipation when
the LTC3447 is used at 100% duty cycle with low input
voltage (See Thermal Considerations in the Applications
Information section).
Low Supply Operation
The LTC3447 will operate with input supply voltages as
low as 2.5V, but the maximum allowable output current
is reduced at this low voltage. Figure 4 shows the reduc-
tion in the maximum output current as a function of input
voltage for various output voltages.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant fre-
quency architectures by preventing subharmonic oscil-
lations at high duty cycles. It is accomplished internally
by adding a compensating ramp to the inductor current
signal at duty cycles in excess of 40%. Normally, this
results in a reduction of maximum inductor peak current
8
SDA
SCL
COMMAND
Figure 4. Maximum Load Current vs Supply Voltage
START
S
1200
1100
1000
900
800
700
ADDRESS
2.5
T
U
A
1-7
= 25°C
3.0
SUPPLY VOLTAGE (V)
3.5
DAC = MIN
R/W
DAC = MAX
8
4.0
4.5
ACK
9
5.0
3447 F04
Figure 6. Typical I
5.5
1-7
DATA
2
C Write Protocol
8
voltage transitions begin once the I
the STOP command.
Slew Rate
The LTC3447 has a slew rate of approximately 11mV/µs.
The slew rate is controlled by the RC time constant of a
low pass fi lter at the voltage DAC output. Figure 5 shows
a typical transition from min to max DAC settings.
for duty cycles >40%; however, the LTC3447 uses a
patent-pending scheme that counteracts this compensat-
ing ramp, which allows the maximum inductor peak current
to remain unaffected throughout all duty cycles.
DAC
The I
DAC for the buck regulator. The output voltage range is
0.69V to 2.05V in 21.6mV steps. The default DAC setting
is 100000 which equates to a 1.38V output voltage. Output
2
C interface is used to control the internal voltage
Figure 5.Transition from DAC = MIN to DAC = MAX
ACK
9
500mV/DIV
200mA/DIV
5V/DIV
BURST MODE OPERATION
V
IN
1-7
= 3.6V
DATA
INDUCTOR CURRENT
100µs/DIV
8
PGOOD
V
OUT
2
C interface receives
ACK
9
COMMAND
ST0P
P
3447 TD02
3447f