LTC1625IGN#TR Linear Technology, LTC1625IGN#TR Datasheet - Page 13

• Manufacturer Part Number: LTC1625IGN#TR
• Description: IC SW REG STEP-DOWN SYNC 16-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1625IGN#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 36 V
• Current - Output: 50mA
• Frequency - Switching: 150kHz
• Voltage - Input: 3.7 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LTC1625IGNTR; Q1127755

APPLICATIONS
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the LTC1625
to exceed its maximum junction temperature rating. Most
of the supply current drives the MOSFET gates unless an
external EXTV
can be estimated from the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC1625CGN
is limited to less than 14mA from a 30V supply:
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked when
operating in continuous mode at high V
EXTV
The LTC1625 contains an internal P-channel MOSFET
switch connected between the EXTV
Whenever the EXTV
regulator shuts off, the switch closes and INTV
supplied via EXTV
allows the MOSFET gate drive and control power to be
derived from the output or other external source during
normal operation. When the output is out of regulation
(start-up, short circuit) power is supplied from the internal
regulator. Do not apply greater than 7V to the EXTV
and ensure that EXTV
Significant efficiency gains can be realized by powering
INTV
the driver and control currents will be scaled by a factor of
Duty Cycle/Efficiency. For 5V regulators this simply means
connecting the EXTV
3.3V and other lower voltage regulators, additional cir-
cuitry is required to derive INTV
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
2. EXTV
T
to be powered from the internal 5.2V regulator resulting
in an efficiency penalty of up to 10% at high input
voltages.
connection for a 5V regulator and provides the highest
efficiency.
J
CC
CC
= 70 C + (14mA)(30V)(130 C/W) = 125 C
from the output, since the V
CC
CC
Connection
left open (or grounded). This will cause INTV
connected directly to V
CC
CC
source is used. The junction temperature
:
CC
U
CC
until EXTV
CC
CC
pin is above 4.7V the internal 5.2V
pin directly to V
INFORMATION
U
V
IN
.
CC
CC
drops below 4.5V. This
power from the output.
OUT
W
IN
CC
. This is the normal
current supplying
OUT
and INTV
IN
.
. However, for
CC
U
power is
CC
CC
pins.
pin
CC
3. EXTV
4. EXTV
5V < V
CONNECTION
V
PUMP
For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
output-derived voltage which has been boosted to
greater than 4.7V. This can be done with either an
inductive boost winding as shown in Figure 5a or a
capacitive charge pump as shown in Figure 5b.
supply is available in the 5V to 7V range (EXTV
it may be used to power EXTV
ible with the MOSFET gate drive requirements.
Figure 5a: Secondary Output Loop and EXTV
OPTIONAL
SEC
EXTV
EXTV
LTC1625
< 7V
2(V
CC
CC
CC
Figure 5b: Capacitive Charge Pump for EXTV
CC
OUT
connected to an output-derived boost network.
connected to an external supply. If an external
PGND
R4
R3
– V
SW
V
TG
BG
TK
IN
D
)
EXTV
FCB
SGND
LTC1625
CC
PGND
+
SW
V
BG
TG
TK
IN
C
V
IN
IN
BAT85
CC
L1
+
providing it is compat-
•
V
C
+
IN
IN
1:N
T1
1N4148
VN2222LL
1 F
LTC1625
0.22 F
CC
•
Connection
+
+
+
CC
CC
C
C
CC
V
OUT
OUT
13
1625 F05a
SEC
C
1 F
< V
BAT85
BAT85
SEC
1625 F05b
to an
V
OUT
V
IN
OUT
),