LTC3828 Datasheet, PDF (13/32 Pages) Linear Technology – Dual 2-Phase Step-Down Controller with Tracking

U
OPERATIO (Refer to Functional Diagram)
3.0
SINGLE PHASE
2.5
DUAL CONTROLLER
2.0
1.5
2-PHASE
DUAL CONTROLLER
1.0
0.5
V_O1 = 5V/3A
V_O2 = 3.3V/3A
0
0
10
20
30
40
INPUT VOLTAGE (V)
3828 F03
Figure 3. RMS Input Current Comparison
LTC3828
APPLICATIO S I FOR ATIO
Output Voltage Tracking
The LTC3828 allows the user to program how the channel
outputs ramp up and down by means of the TRCKSS pins.
Through these pins, the channel outputs can be set up to
either coincidentally or ratiometrically tracking, as shown
in Figure 4.
The TRCKSS pins act as clamps on the channels’ refer-
ence voltages. V_OUT is referenced to the TRCKSS voltage
when the TRCKSS < 0.8V and to the internal precision
reference when TRCKSS > 0.8V.
To implement the tracking in Figure 4a, connect an extra
resistive divider to the output of the master channel and
connect its midpoint to the slave channel’s TRCKSS pin.
The ratio of this divider should be selected the same as that
of channel 2’s feedback divider (Figure 5). In this tracking
mode, the master channel’s output must be set higher
than slave channel’s output. To implement the ratiomet-
ric tracking in Figure 4b, no extra divider is needed; simply
connect one of TRCKSS pins to the other channel’s V_FB pin
(Figure 5).
V_OUT1
V_OUT1
V_OUT2
V_OUT2
TIME
(4a) Coincident Tracking
TIME
3828 F04
(4b) Ratiometric Tracking
Figure 4. Two Different Modes of Output Voltage Tracking
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