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 F15
Figure 15. Ratiometric Tracking Waveforms from Figure 16 Circuit
Ratiometric Tracking Example
This example converts the coincident tracking example to
the ratiometric tracking profile shown in Figure 15, using
two slave supplies and a master ramp signal (not a master
ramp supply). The ramp rate of the master signal remains
unchanged (Step 1), the minimum load resistance of the
slave loads remains unchanged (Step 2), and there is no
delay in ratiometric tracking. Only Step 3 of the three-step
design procedure needs to be considered. In this example,
1.8V MODULE
3.3V IN OUT
SENSE
RX1
100Ω
Q1
IRF7413Z
10Ω
1.8V
SLAVE1
the ramp rate of the 1.8V slave supply is 60V/s, and the
ramp rate of the 2.5V supply is 83.3V/s. Always verify that
the chosen ramp rate will allow the supplies to ramp-up
completely before RAMPBUF reaches VCC. If the 1.8V slave
supply were to ramp up at 50V/s it would only reach 1.65V
because the RAMPBUF signal would reach its final value
of VCC = 3.3V before the slave supply reached 1.8V.
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
60 V
s
s
⎞
⎠⎟
=
25kΩ
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
24.9k
RTB2
18.2k
RTA1
7.68k
RTA2
VIN
5.36k
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 F16
RFB1
15.0k
RFA1
9.53k
RFB2
15.0k
VIN
10k
RFA2
5.76k
STATUS
NC
Choose RTB = 24.9kΩ.
Since no offset or delay is required, Equation 5c applies:
ΔV = 0V
From Equation 6:
RTA =
0.8V
+
0.8V
0.8V − 0.8V
+
0V
= 7.61kΩ
15.0kΩ 9.53kΩ 24.9kΩ 24.9kΩ
Choose RTA = 7.68kΩ.
Figure 16. Ratiometric Tracking Example
2926fa
20
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