LTC2926IUFD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2926IUFD' PDF : 28 Pages View PDF
LTC2926
APPLICATIO S I FOR ATIO
500mV/DIV
SLAVE2
SLAVE1
500mV/DIV
5ms/DIV
5ms/DIV
2926 F19
Figure 19. Supply Sequencing Waveforms from Figure 20 Circuit
Supply Sequencing Example
In Figure 19, the two slave supplies are sequenced using a
master ramp signal. As in the ratiometric tracking example,
the master signal ramps up at 100V/s, and the minimum
slave loads are the same as the coincident example, so
steps 1 and 2 remain the same. The 1.8V slave 1 supply
ramps up at 1000V/s beginning 10ms after the master
signal starts to ramp up. The 2.5V slave 2 supply ramps
up at 1000V/s beginning 20ms after the master signal
1.8V MODULE
3.3V IN OUT
SENSE
RX1
100Ω
Q1
IRF7413Z
10Ω
1.8V
SLAVE1
2.5V MODULE
3.3V IN OUT
SENSE
RX2
100Ω 3.3V
VIN
0.1µF
CMGATE
0.1µF
Q2
IRF7413Z
10Ω
2.5V
SLAVE2
RTB1
1.50k
RTB2
2.49k
RTA1
2.94k
RTA2
VIN
1.33k
10k
FAULT
ON/OFF
VCC
D1
MGATE RAMP SGATE1 SGATE2
D2
S1
RAMPBUF
S2
TRACK1
FB1
LTC2926
TRACK2
FB2
FAULT
ON
GND
STATUS/PGI
PGTMR
RSGATE
CPGTMR
1µF
2926 F20
RFB1
15.0k
RFA1
9.53k
RFB2
24.9k
VIN
10k
RFA2
9.53k
STATUS
NC
starts to ramp up. Note that not every combination of
ramp rates and delays is possible. Small delays and large
ratios of slave ramp rate to master ramp rate may result
in solutions that require negative resistors. In such cases,
either the delay must be increased or the ratio of slave
ramp rate to master ramp rate must be reduced.
3. Solve for the tracking resistors that set the desired ramp
rate and voltage offset or time delay of the slave supply.
From Equation 4:
RTB
=
⎛
15.0kΩ• ⎝⎜
100 V
1000 V
s
s
⎞
⎠⎟
=
1.5kΩ
Choose RTB = 1.50kΩ.
Since a delay is required, Equation 5b applies:
ΔV = 100V/s • 10ms = 1V
From Equation 6:
RTA =
0.8V
+
0.8V
0.8V − 0.8V
+
1V
= 2.96kΩ
15.0kΩ 9.53kΩ 1.50kΩ 1.50kΩ
Choose RTA = 2.94kΩ.
Note that the values of RFA2 and RFB2 are larger than those
of the Coincident Tracking Example. Larger feedback resis-
tor values resulted in larger tracking resistor values for
RTA2 and RTB2, which limits the maximum TRACK2 pin
current to <1mA; see Final Sanity Checks.
Figure 20. Supply Sequencing Example
2926fa
22
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