LTC3526 Linear Technology, LTC3526 Datasheet - Page 9

• Manufacturer Part Number: LTC3526
• Description: 500mA 1MHz Synchronous Step-Up DC/DC Converters
• Manufacturer: Linear Technology

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Zero Current Comparator
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifi er
when this current reduces to approximately 30mA. This
prevents the inductor current from reversing in polarity,
improving effi ciency at light loads.
Synchronous Rectifi er
To control inrush current and to prevent the inductor
current from running away when V
P-channel MOSFET synchronous rectifi er is only enabled
when V
Anti-Ringing Control
The anti-ringing control connects a resistor across the
inductor to prevent high frequency ringing on the SW pin
during discontinuous current mode operation. Although
the ringing of the resonant circuit formed by L and C
(capacitance on SW pin) is low energy, it can cause EMI
radiation.
Output Disconnect
The LTC3526/LTC3526B are designed to allow true output
disconnect by eliminating body diode conduction of the
internal P-channel MOSFET rectifi er. This allows for V
to go to zero volts during shutdown, drawing no current
from the input source. It also allows for inrush current
limiting at turn-on, minimizing surge currents seen by the
input supply. Note that to obtain the advantages of output
disconnect, there must not be an external Schottky diode
connected between the SW pin and V
connect feature also allows V
any reverse current into a battery connected to V
Thermal Shutdown
If the die temperature exceeds 160°C, the LTC3526/
LTC3526B will go into thermal shutdown. All switches
will be off and the soft-start capacitor will be discharged.
The device will be enabled again when the die temperature
drops by about 15°C.
OPERATION
OUT
> (V
IN
+ 0.24V).
(Refer to Block Diagram)
OUT
to be pulled high, without
OUT
OUT
is close to V
. The output dis-
IN
IN
.
, the
OUT
SW
Burst Mode OPERATION
The LTC3526 will automatically enter Burst Mode opera-
tion at light load and return to fi xed frequency PWM mode
when the load increases. Refer to the Typical Performance
Characteristics to see the output load Burst Mode thresh-
old current vs V
operation is entered can be changed by adjusting the
inductor value. Raising the inductor value will lower the
load current at which Burst Mode operation is entered.
In Burst Mode operation, the LTC3526 still switches at a
fi xed frequency of 1MHz, using the same error amplifi er
and loop compensation for peak current mode control.
This control method eliminates any output transient
when switching between modes. In Burst Mode opera-
tion, energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3526 transitions to
sleep mode where the outputs are off and the LTC3526
consumes only 9μA of quiescent current from V
the output voltage droops slightly, switching resumes.
This maximizes effi ciency at very light loads by minimizing
switching and quiescent losses. Burst Mode output voltage
ripple, which is typically 1% peak-to-peak, can be reduced
by using more output capacitance (10μF or greater), or
with a small capacitor (10pF to 50pF) connected between
V
As the load current increases, the LTC3526 will automati-
cally leave Burst Mode operation. Note that larger output
capacitor values may cause this transition to occur at lighter
loads. Once the LTC3526 has left Burst Mode operation and
returned to normal operation, it will remain there until the
output load is reduced below the burst threshold.
Burst Mode operation is inhibited during start-up and soft-
start and until V
The LTC3526B features continuous PWM operation at
1MHz. At very light loads, the LTC3526B will exhibit
pulse-skip operation.
OUT
and FB.
IN
OUT
LTC3526/LTC3526B
. The load current at which Burst Mode
is at least 0.24V greater than V
OUT
. When
IN
3526bfb
9
.