NCP3122 Datasheet, PDF (26/42 Pages) ON Semiconductor – Dual 2.0 A, Step-Down DC/DC Switching Regulator

NCP3122
Tracking
Voltage tracking is enabled by applying a ramp voltage to
the TRACK pin. When the voltage on the TRACK pin is
below 0.8 V, the feedback voltage will regulate to this
tracking voltage. When the tracking voltage exceeds 0.8 V,
tracking is disabled and the feedback voltage will regulate
to the internal reference voltage.
In this start−up sequence, the tracking pin is used to match
the output voltage ramps exactly. Higher output voltage will
continue to rise past the lower regulated point. This is
achieved by dividing the higher output voltage by the same
ratio as the lower voltage feedback components and
connecting the divided voltage into the TRACK pin of the
lower voltage. Track pins must be tied high in the normal
operation (except in the tracking mode).
The output voltage during tracking can be calculated with
the following equation:
ǒ Ǔ V_OUT + V_TRACK
1
)
R5
R6
V_TRACK t 0.8 V
AVIN
C3
VIN
C13
R8
R10
Enable
Disable
Cmaster
GND
PG1
PG2
EN1
SEQ1
EN2
SEQ2
TRACK1
TRACK2
R9
GND
NCP3122
SW1
VIN
VIN
VIN
VIN
VIN
VIN
SW2
R11
L1
D1
GND
C9 C10
GND GND
L2
D2
GND
R7
GND
C4
GND
OUT1
R1
R5
C7
R2
R6
GND
GND
GND
OUT2
R3
C8
R4
GND
GND
Cmaster
VOUT1
VOUT2
C_master
Figure 54. Tracking Configuration
http://onsemi.com
26