LTC3892-1_15 Datasheet, PDF (22/36 Pages) Linear Technology – 60V Low IQ, Dual, 2-Phase Synchronous Step-Down DC/DC Controller

LTC3892/LTC3892-1
Applications Information
Alternatively, the TRACK/SS1 and TRACK/SS2 pins can
be used to track two (or more) supplies during start-up,
as shown qualitatively in Figures 6a and 6b. To do this, a
resistor divider should be connected from the master sup-
ply (V_X) to the TRACK/SS pin of the slave supply (V_OUT),
as shown in Figure 7. During start-up V_OUT will track V_X
according to the ratio set by the resistor divider:
V_{X =} R_{A •} R_TRACKA +R_TRACKB
V_OUT R_TRACKA
R_A +R_B
For coincident tracking (V_OUT = V_X during start-up),
R_A = R_TRACKA
R_B = R_TRACKB
V_X(MASTER)
V_OUT(SLAVE)
TIME
(6a) Coincident Tracking
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V_X(MASTER)
V_OUT(SLAVE)
TIME
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(6b) Ratiometric Tracking
Figure 6. Two Different Modes of Output Voltage Tracking
V_OUT
R_B
R_A
V_X
R_TRACKB
R_TRACKA
V_FB
1/2 LTC3892/
LTC3892-1
TRACK/SS
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Figure 7. Using the TRACK/SS Pin for Tracking
DRV_CC and INTV_CC Regulators and EXTV_CC
(OPTI-DRIVE)
The LTC3892/LTC3892-1 features two separate internal
P-channel low dropout linear regulators (LDO) that supply
power at the DRV_CC pin from either the V_IN supply pin or the
EXTV_CC pin depending on the connections of the EXTV_CC,
DRVSET, and DRVUV pins. A third P-channel LDO sup-
plies power at the INTV_CC pin from the DRV_CC pin. DRV_CC
powers the gate drivers whereas INTV_CC powers much of
the LTC3892/LTC3892-1’s internal circuitry. The V_IN LDO
and the EXTV_CC LDO regulate DRV_CC between 5V to 10V,
depending on how the DRVSET pin is set. Each of these
LDOs can supply a peak current of at least 50mA and must
be bypassed to ground with a minimum of 4.7μF ceramic
capacitor. Good bypassing is needed to supply the high
transient currents required by the MOSFET gate drivers and
to prevent interaction between the channels. The INTV_CC
supply must be bypassed with a 0.1μF ceramic capacitor.
The DRVSET pin programs the DRV_CC supply voltage and
the DRVUV pin selects different DRV_CC UVLO and EXTV_CC
switchover threshold voltages. Table 2a summarizes the
different DRVSET pin configurations along with the volt-
age settings that go with each configuration. Table 2b
summarizes the different DRVUV pin settings. Tying the
DRVSET pin to INTV_CC programs DRV_CC to 10V. Tying the
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