SI9165_07 Datasheet, PDF (6/10 Pages) Vishay Siliconix – High Frequency 600-mA Synchronous Buck/Boost Converter

Si9165
Vishay Siliconix
FUNCTIONAL BLOCK DIAGRAM
V_REF
FB
COMP
Reference
Threshold
Generator
SYNC
R_OSC
V_O
Oscillator
C_OSC
Soft-Start
Timer
1.0 V
Ramp
V_DD
Positive
Supply
UVLO
SD
V_S
V_IN/OUT
POR
Bias
Generator
OTP
PWM
Modulator
0.5 V
PSM
Modulator
PWM_EN
PWM/PSM
Select
PSM_EN
PWM_IN
Drivers
PSM_IN
P
COIL
N
PWM/PSM
MODE
Negative
Return and
Substrate
GND
PGND
DETAIL OPERATIONAL DESCRIPTION
Start-Up
The UVLO circuit prevents the internal MOSFET switches
and oscillator circuit from turning on, if the voltage on V_DD pin
is less than 2.5 V. With typical UVLO hysteresis of 0.1 V,
controller is continuously powered on until the V_DD voltage
drops below 2.4 V. This hysteresis prevents the converter
from oscillating during the start-up phase and unintentionally
locking up the system. Once the V_DD voltage exceeds the
UVLO threshold, and with no other shutdown condition
detected, an internal Power-On-Reset timer is activated
while most circuitry, except the output driver, are turned on.
After the POR timeout of about 1 ms, the internal soft-start
capacitor is allowed to charge. When the soft-start capacitor
voltage reaches 0.5 V, the PWM circuit is enabled.
Thereafter, the constant current charging the soft-start
capacitor will force the output voltage to rise gradually
without overshooting. To prevent negative undershoot, the
synchronous switch is tri-stated until the duty cycle reaches
about 10 %. In tri-state, the high-side P-Channel MOSFET is
turned off by pulling up the gate voltage to V_S potential. The
low-side N-Channel MOSFET is turned off by pulling down
the gate voltage to PGND potential. Note that the Si9165 will
always soft starts in the PWM mode regardless of the voltage
level on the PWM/PSM pin.
Shutdown
The Si9165 is designed to conserve as much battery life as
possible by decreasing current consumption of IC during
normal operation as well as the shutdown mode. With logic
low level on the SD pin, current consumption of the Si9165 is
decreased to less than 1 µA by shutting off most of the
circuits. The logic high enables the controller and starts up as
described in "Start-Up" section above.
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Document Number: 70845
S-72058-Rev. D, 08-Oct-07