SI9169 Datasheet, PDF (8/8 Pages) Vishay Siliconix – High Frequency 1-A Synchronous Buck/Boost Converter

Si9169
Vishay Siliconix
Error Amplifier
The error amplifier gain-bandwidth product and slew rate is
critical parameters which determines the transient response of
converter. The transient response is function of both small and
large signal response. The small signal is the converter closed
loop bandwidth and phase margin while the large signal is
determined by the error amplifier dv/dt and the inductor di/dt
slew rate. Besides the inductance value, error amplifier
determines the converter response time. In order to minimize
the response time, the Si9169 is designed with 2-MHz error
amplifier gain-bandwidth product to generate the widest
converter bandwidth and 3.5 V/msec slew rate for ultra-fast
large signal response.
Oscillator
The oscillator is designed to operate up to 2-MHz minimal. The
2-MHz operating frequency allows the converter to minimize
the inductor and capacitor size, improving the power density
of the converter. Even with 2-MHz switching frequency,
quiescent current is only 500 mA with unique power saving
circuit design. The switching frequency is easily programmed
by attaching a resistor to R_OSC pin. See oscillator frequency
versus R_OSC curve to select the proper values for desired
operating frequency. The tolerance on the operating
frequency is "20% with 1% tolerance resistor.
Synchronization
The synchronization to external clock is easily accomplished
by connecting the external clock into the SYNC pin. A logic
high to low transition synchronizes the clock. The external
clock frequency must be within 1.2 to 1.5 times the internal
clock frequency.
Break-Before-Make Timing
A proper BBM time is essential in order to prevent
shoot-through current and maintain high efficiency. The
break-before-make time is set internally at 20 ns @ V_S = 3.6 V.
The high and low-side MOSFET drain voltages are monitored
and when the drain voltage reaches the 1.75 V below or above
its initial starting voltage, 20 ns BBM time is set before the other
switch turns on. The maximum controllable duty cycle is
limited by the BBM time. Since the BBM time is fixed,
maximum controllable duty cycle will vary depending on the
switching frequency.
Output MOSFET Stage
The high- and low-side switches are integrated to provide
optimum performance and to minimize the overall converter
size. Both, high and low-side switches are designed to handle
up to 1 A of continuous current. The MOSFET switches were
designed to minimize the gate charge loss as well as the
conduction loss. For the high frequency operation, switching
losses can exceed conduction loss, if the switches are
designed incorrectly. Under full load, efficiency of 90% is
accomplished with 3.6-V battery voltage in both buck and
boost modes (+2.7-V output voltage for buck mode and +5-V
output voltage for boost mode).
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Document Number: 70945
S-40695—Rev. D, 19-Apr-04