LTM4616
APPLICATIONS INFORMATION
coincident tracking. The LTM4616 uses an accurate 10k
resistor internally for the top feedback resistor. Figure 5
shows an example of coincident tracking:
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the mas-
ter’s track pin. As mentioned above, the TRACK pin has
a control range from 0V to 0.596V. The master’s TRACK
pin slew rate is directly equal to the master’s output slew
rate in Volts/Time:
⎛
⎜
⎝
⎞
10k
RTA
Slave = 1+
• VTRACK
⎟
⎠
MR
V
TRACK
V
TRACK
is the track ramp applied to the slave’s track pin.
has a control range of 0V to 0.596V, or the internal
• 10k = RTB
SR
reference voltage. When the master’s output is divided
down with the same resistor values used to set the slave’s
output, then the slave will coincident track with the master
untilitreachesitsfinalvalue.Themasterwillcontinuetoits
final value from the slave’s regulation point. Voltage track-
where MR is the master’s output slew rate and SR is the
slave’s output slew rate in Volts/Time. When coincident
tracking is desired, then MR and SR are equal, thus R
TB
is equal to 10k. R is derived from equation:
TA
0.596V
ing is disabled when V
is more than 0.596V. R in
TRACK
TA
RTA
=
VTRACK
V
V
Figure 5 will be equal to R for coincident tracking.
FB
FB
FB
+
–
10k RFB
RTB
Thetrackpinofthemastercanbecontrolledbyanexternal
ramp or by R and C in Figure 5 referenced to V .
SR
SR
IN
where V is the feedback voltage reference of the regula-
FB
The RC ramp time can be programmed using equation:
tor and V
is 0.596V. Since R is equal to the 10k
TRACK
TB
top feedback resistor of the slave regulator in coincident
⎛
⎞
⎛
⎞
0.596V
t = – ln 1–
•RSR • CSR
tracking, then R is equal to R
with V = V
.
⎜
⎟
TA
FB2
FB
TRACK
⎜
⎟
V
⎝
⎠
⎝
⎠
IN
CLKIN1
V
4V TO 5.5V
SW1
CLKIN1 CLKOUT1 CLKIN2 CLKOUT2
IN
MASTER
3.3V/7A
V
IN1
V
OUT1
SV
FB1
IN1
R
V
IN
RUN
10µF
FB1
RUN1
I
TH1
2.21k
100µF
PLLLPF1
MODE1
I
THM1
50k
50k
R
SR
PGOOD1
BSEL1
MGN1
PHMODE1
TRACK1
LTM4616
SLAVE
1.5V/8A
V
V
IN2
OUT2
FB2
C
SR
SV
IN2
R
RUN
10µF
FB2
RUN2
I
TH2
6.65k
100µF
100µF
PLLLPF2
MODE2
PHMODE2
TRACK2
I
MASTER
3.3V
THM2
PGOOD2
PGOOD
BSEL
R
BSEL2
MGN2
TB
10k
R
TA
SW2
SGND1
GND1
SGND2
GND2
6.65k
4616 F05
FOR TRACK1:
1. TIE TO VIN TO DISABLE TRACK WITH DEFAULT 100µs SOFT START
2. APPLY A CONTROL RAMP WITH R AND C TIED TO V WITH t = –(ln(1–0.596/V ) • R • C ))
SR
SR
IN
IN
SR
SR
3. APPLY AN EXTERNAL TRACKING RAMP DIRECTLY
Figure 5. Dual Outputs (3.3V and 1.5V) with Tracking
4616fe
16
For more information www.linear.com/LTM4616
LINEAR_DIMENSIONS [ Linear Dimensions ]
