SIP12503 Datasheet, PDF (5/11 Pages) Vishay Siliconix – 500-mA - Adjustable Boost Converter for Single or Dual Cell

FUNCTIONAL BLOCK DIAGRAM
V_OUT
Compensation
FB
-
E/A
+
XSHD
Reference and Soft-Start
SiP12503
Vishay Siliconix
V_IN
Over Voltage
Start-Up
Antiringing SW
Oscillator
+
PWM
-
PFM
Driver
GND
LX
DETAILED OPERATION
SiP12503 is a 300 kHz boost converter IC, packaged in 6 pin
MLP33 PowerPAK^TM package. With start-up from input
voltages as low as 0.65 V, this device features fixed
frequency voltage mode PWM control with internal frequency
compensation. With its low R_DS(on) internal power MOSFET,
this device maintains high efficiency over a wide range of
load current. Under light load conditions, it switches to in
PFM mode to maintain high efficiency. A FB pin is available
to adjust the output voltage.
Low Voltage Start-Up
SiP12503 is designed to start-up at input voltage of typically
0.65 V. At start-up, V_OUT is lower than V_IN due to the voltage
drop of the Schottky diode. Therefore, the device uses V_IN as
the power source for its control logic and internal gate drive,
until V_OUT exceeds V_IN. During the start-up interval, the
boost switch’s conduction interval during each cycle is
determined by the time taken for the inductor current to reach
internal current limit, followed by a fixed off time before the
switch is allowed to turn on again. Once V_OUT exceeds V_IN,
the device uses V_OUT as the IC’s power source. When V_OUT
exceeds 1.89 V, the device engages is built-in soft-start
circuitry.
Soft-Start
During soft-start, the loop compensation guarantees the slow
increase of output voltage, so that no large voltage overshoot
or inrush current transients occur when the soft-start period
ends.
PWM operation
After the soft-start interval is over, the device works in PWM
operation with a fixed frequency of 300 kHz, with automatic
switch-over to PFM operation during light load conditions.
PFM Operation
When operating into light loads, the SiP12502 automatically
switches to PFM operation. This reduces gate charge losses
in the boost switch, hence raising converter efficiency.
Document Number: 73579
S09-1454-Rev. B, 03-Aug-09
Over Voltage Protection
If the output voltage is above 10 % of the regulation voltage,
the device will turn off the internal power mosfet and wait until
the output voltage fails below the regulation voltage, then the
PWM operation is enabled again.
Thermal Shutdown Protection
If the internal device temperature rises above 160 °C, the
device will turn off the internal power MOSFET. Once the die
temperature falls below 140 °C, then the device performs a
new soft-start cycle, and the converter resumes normal
operation.
Antiringing Control
The antiringing control circuitry prevents high frequency
ringing at the LX pin as the inductor current goes to zero by
damping the resonant circuit formed by L and C_LX
(capacitance on LX pin). When the IC is shutdown, this
antiringing switch is also turned on.
APPLICATION INFORMATION
Setting the Adjustable Output Voltage
The SiP12503 regulated output can be adjusted from 1.8 V
to 5.0 V via a resistor divider network from V_OUT to GND. R1
and R2 should be kept in the 50 kΩ to 100 kΩ range for low
power consumption while maintaing adequate noise
immunity. The value of R1 is calculated using the following
formula:
R1 = R2 * [(V_OUT/V_FB) - 1]
V_FB = 0.6 V
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