LTC1436A-PLL View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1436A-PLL' PDF : 28 Pages View PDF
LTC1436A
LTC1436-PLL-A/LTC1437A
APPLICATIONS INFORMATION
+
VIN
CIN
LTC1436A VIN
LTC1437A
TGL
EXTVCC TGS
SW
BG
N-CH
N-CH
N-CH
+
BAT85
1µF
0.22µF
VN2222LL
L1
RSENSE
+
BAT85
BAT85
COUT
PGND
1436 F04b
Figure 4b. Capacitive Charge Pump for EXT VCC
Topside MOSFET Driver Supply (CB, DB)
An external bootstrap capacitor CB connected to the Boost
pin supplies the gate drive voltage for the topside
MOSFET(s). Capacitor CB in the functional diagram is
charged through diode DB from INTVCC when the SW pin
is low. When one of the topside MOSFET(s) is to be turned
on, the driver places the CB voltage across the gate source
of the desired MOSFET. This enhances the MOSFET and
turns on the topside switch. The switch node voltage SW
rises to VIN and the Boost pin rises to VIN + INTVCC. The
value of the boost capacitor CB needs to be 100 times
greater than the total input capacitance of the topside
MOSFET(s). In most applications 0.1µF is adequate. The
reverse breakdown on DB must be greater than VIN(MAX).
Output Voltage Programming
The output voltage is pin selectable for all members of the
LTC1436A/LTC1437A family. The output voltage is
selected by the VPROG pin as follows:
VPROG = 0V
VPROG = INTVCC
VPROG = Open (DC)
VOUT = 3.3V
VOUT = 5V
VOUT = Adjustable
The LTC1436A/LTC1437A family also has remote output
voltage sense capability. The top of an internal resistive
divider is connected to VOSENSE. For fixed 3.3V and 5V
output voltage applications the VOSENSE pin is connected
to the output voltage as shown in Figure 5a. When using
an external resistive divider, the VPROG pin is left open (DC)
and the VOSENSE pin is connected to the feedback resistors
as shown in Figure 5b.
VPROG
LTC1436A VOSENSE
LTC1437A
SGND
GND: VOUT = 3.3V
INTVCC: VOUT = 5V
+
COUT
VOUT
1436 F05a
Figure 5a. LTC1436A/LTC1437A Fixed Output Applications
VPROG
LTC1436A VOSENSE
LTC1437A
SGND
1.19V ≤ VOUT ≤ 9V
OPEN (DC)
R2
100pF R1
( ) VOUT = 1.19V
1+
R2
R1
1436 F05b
Figure 5b. LTC1436A/LTC1437A Adjustable Applications
Power-On Reset Function (POR)
The power-on reset function monitors the output voltage
and turns on an open drain device when it is out of
regulation. An external pull-up resistor is required on the
POR pin.
When power is first applied or when coming out of
shutdown, the POR output is pulled to ground. When the
output voltage rises above a level which is 5% below the
final regulated output value, an internal counter starts.
After counting 216 (65536) clock cycles, the POR pull-
down device turns off.
The POR output will go low whenever the output voltage
drops below 7.5% of its regulated value for longer than
approximately 30µs, signaling an out-of-regulation condi-
tion. In shutdown, the POR output is pulled low even if the
regulator’s output is held up by an external source.
Run/Soft Start Function
The RUN/SS pin is a dual purpose pin that provides the
soft start function and a means to shut down the
LTC1436A/LTC1437A. Soft start reduces surge currents
from VIN by gradually increasing the internal current limit.
Power supply sequencing can also be accomplished
using this pin.
16
Share Link: 
