LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 27

• Manufacturer Part Number: LTC3829EFE#PBF
• Description: IC BUCK SYNC ADJ 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3829EFE#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

applicaTions inForMaTion
Nonlinear control is only enabled when V
UV and OV window. It should be enabled only for forced
continuous mode of operation.
Once nonlinear control is enabled, the top gate of all chan-
nels will turn on if:
The top gate of all channels will turn off if:
where V
V
Soft-Start and Tracking
The LTC3829 has the ability to either soft-start by itself
with a capacitor or track the output of another channel or
external supply. When the controller is configured to soft-
start by itself, a capacitor should be connected to its TK/SS
pin. The controller is in the shutdown state if its RUN pin
voltage is below 1.22V and its TK/SS pin is actively pulled
to ground in this shutdown state. If the RUN pin voltage
is above 1.22V, the controller powers up. A soft-start cur-
rent of 1.25µA then starts to charge the TK/SS soft-start
capacitor. Note that soft-start or tracking is achieved not
by limiting the maximum output current of the control-
ler but by controlling the output ramp voltage according
to the ramp rate on the TK/SS pin. Current foldback is
FB
V
V
is the feedback voltage.
FB
FB
=
=
REF
V
V
REF
REF
is the reference voltage, normally at 0.6V, and
–
+
0 5
0 5
. –
. –
5
5
V
V
IFAST
IFAST
• .
1 2
FB
is within the
disabled during this phase to ensure smooth soft-start or
tracking. The soft-start or tracking range is defined to be
the voltage range from 0V to 0.6V on the TK/SS pin. The
total soft-start time can be calculated as:
Regardless of the mode selected by the MODE pin, the
controller always starts in discontinuous mode up to TK/SS
= 0.5V. Between TK/SS = 0.5V and 0.54V, it will operate in
forced continuous mode and revert to the selected mode
once TK/SS > 0.54V. The output ripple is minimized dur-
ing the 40mV forced continuous mode window ensuring
a clean PGOOD signal. When the channel is configured
to track another supply, the feedback voltage of the other
supply is duplicated by a resistor divider and applied to
the TK/SS pin. Therefore, the voltage ramp rate on this
pin is determined by the ramp rate of the other supply’s
voltage. Note that the small soft-start capacitor charging
current is always flowing, producing a small offset error.
To minimize this error, select the tracking resistive divider
value to be small enough to make this error negligible.
In order to track down another channel or supply after
the soft-start phase expires, the LTC3829 is forced into
continuous mode of operation as soon as V
undervoltage threshold of 0.54V regardless of the setting
on the MODE pin. However, the LTC3829 should always be
set in forced continuous mode tracking down when there
is no load. After TK/SS drops below 0.1V, the controller
operates in discontinuous mode.
t
SOFTSTART
= 0 6
. •
1 25
.
C
SS
µA
LTC3829
FB
is below the

3829f