LTM4604 データシートの表示（PDF） - Linear Technology
部品番号
コンポーネント説明
メーカー
LTM4604 Datasheet PDF : 20 Pages
| |||
LTM4604
APPLICATIONS INFORMATION
Run Enable and Soft-Start
The RUN/SS pin provides dual functions of enable and
soft-start control. The RUN/SS pin is used to control
turn on of the LTM4604. While this pin is below 0.5V, the
LTM4604 will be in a 7μA low quiescent current state. A
0.8V threshold will enable the LTM4604. This pin can be
used to sequence LTM4604 devices. The soft-start control
is provided by a 1M pull-up resistor (RSS) and a 1000pF
capacitor (CSS) as drawn in the Block Diagram. An external
capacitor can be applied to the RUN/SS pin to increase the
soft-start time. A typical value is 0.01μF. The approximate
equation for soft-start is:
( ) tSOFTSTART
=
⎛
ln⎝⎜ VIN
VIN ⎞
– 1.8V⎠⎟
• RSS
CSS
+ CSSEXT
where RSS and CSS are shown in the Block Diagram of
Figure 1, 1.8V is the soft-start upper range, and CSSEXT
is the additional capacitance for further soft-start contol.
The soft-start function can also be used to control the
output ramp-up time, so that another regulator can be
easily tracked. An independent ramp control signal can
be applied to the master ramp, otherwise, connect the
TRACK pin to VIN to disable tracking.
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK pin. The output can be tracked up and
down with another regulator. The master regulator’s
output is divided down with an external resistor divider
that is the same as the slave regulator’s feedback divider
to implement coincident tracking. The LTM4604 uses a
very accurate 4.99k resistor for the top feedback resistor.
Figure 2 shows an example of coincident tracking.
VTRACK
=
RFB2
4.99k + RFB2
•
VMASTER
VTRACK is the track ramp applied to the slave’s TRACK pin.
VTRACK applies the track reference for the slave output up
to the point of the programmed value at which VTRACK
proceeds beyond the 0.8V reference value. The VTRACK
pin must go beyond 0.8V to ensure the slave output has
reached its final value. Load current must be present for
proper tracking.
10
VIN
5V
CIN1
10μF
6.3V
X5R OR X7R
CSSEXT
VIN
PGOOD VOUT
LTM4604
COMP
FB
RUN/SS TRACK
GND
RAMP
CONTROL
OR VIN
RFB3
1.62k
COUT1
22μF
6.3V ×3
X5R OR
X7R
VMASTER
3.3V
4A
VIN
5V
CIN2
10μF
6.3V
X5R OR X7R
VIN
PGOOD VOUT
LTM4604
COMP
FB
RUN/SS TRACK
GND
RFB2
5.76k
RFB
5.76k
COUT2
22μF
6.3V ×3
X5R OR
X7R
VSLAVE
1.5V
4A
RFB1
4.99k
4604 F02
Figure 2
MASTER OUTPUT
SLAVE OUTPUT
TIME
Figure 3
4604 F03
4604f
Share Link: 