SI9169 Datasheet, PDF (6/8 Pages) Vishay Siliconix – High Frequency 1-A Synchronous Buck/Boost Converter

Si9169
Vishay Siliconix
FUNCTIONAL BLOCK DIAGRAM
V_REF
FB
COMP
Reference
Threshold
Generator
SYNC
R_OSC
V_O
Oscillator
C_OSC
Soft-Start
Timer
V_DD
Positive
Supply
UVLO
SD
V_S
V_IN/OUT
POR
Bias
Generator
OTP
1.0 V
Ramp
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 Re-
turn 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
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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
Si9169 will always soft starts in the PWM mode regardless of
the voltage level on the PWM/PSM pin.
Shutdown
The Si9169 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 Si9169 is
decreased to less than 1 mA by shutting off most of the circuits.
The logic high enables the controller and starts up as
described in “Start-Up” section above.
Document Number: 70945
S-40695—Rev. D, 19-Apr-04