Datasheet

ADP1850 Data Sheet
Rev. A | Page 24 of 32
Another ratiometric tracking configuration is having the slave
channel rise more quickly than the master channel, as shown in
Figure 40 and Figure 41. The tracking circuits in Figure 39 and
Figure 41 are virtually identical with the exception that R
TRKB
>
R
TRKT
as shown in Figure 41.
INDEPDENDENT POWER STAGE INPUT VOLTAGE
In addition to the single power supply configuration, the power
stage input voltage of the dc-to-dc converter can come from a
different voltage supply, as illustrated in Figure 42. The range of
the power stage input voltage (V
PIN
) is 1 V to 20 V. For instance,
the bias input voltage (V
IN
) is 5 V, V
PIN
can be as low as 1 V or as
high as 20 V. The user needs to make sure that the minimum
or the maximum duty cycle is not violated in this operating
condition. Furthermore, note that R
RAMP
is connected to V
PIN
.
TIME
SLAVE VOLTAGE
MASTER
V
OLTA
G
E
VOLTAGE (V)
09440-040
V
IN
= 2.7V TO 20V
VIN
ADP1850
DH1
FB1
DL1
PGND1
SW1
V
OUT1
V
PIN
= 1V TO 20
V
RAMP1
R
RAMP1
DH2
RAMP2
FB2
DL2
PGND2
SW2
V
OUT2
V
PIN
= 1V TO 20V
R
RAMP2
09440-042
Figure 40. Ratiometric Tracking (Slave Channel Has a Faster Ramp Rate)
ADP1850
EN2EN1
EN
FB2
FB1TRK1
SS1
VCCO
TRK2
SS2
10kΩ
45.3kΩ
R
TRKB
10kΩ
R
TRKT
5kΩ
2.2V
3.3
V
V
OUT1_MASTER
C
SS2
20nF
C
SS1
100n
F
R
BOT
10kΩ
R
TOP
20kΩ
1.8V
V
OUT2_SLAVE
09440-041
Figure 41. Example of a Ratiometric Tracking Circuit (Slave Channel Has a
Faster Ramp Rate)
Figure 42. Independent Power Stage Input Voltage (Simplified Schematic)