LT1767EMS8-5#PBF Linear Technology, LT1767EMS8-5#PBF Datasheet - Page 10

• Manufacturer Part Number: LT1767EMS8-5#PBF
• Description: IC SW REG STEP-DOWN 5V 8-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1767EMS8-5#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1.5A
• Frequency - Switching: 1.25MHz
• Voltage - Input: 3 ~ 25 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Primary Input Voltage: 15V
• No. Of Outputs: 1
• Output Voltage: 5V
• Output Current: 1.5A
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Range: 3V To 25V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
suitable, but the ESR should be <1 to ensure it can be
fully recharged during the off time of the switch. The
capacitor value is derived from worst-case conditions of
700ns on-time, 50mA boost current, and 0.7V discharge
ripple. This value is then guard banded by 2x for secondary
factors such as capacitor tolerance, ESR and temperature
effects. The boost capacitor value could be reduced under
less demanding conditions, but this will not improve
circuit operation or efficiency. Under low input voltage and
low load conditions, a higher value capacitor will reduce
discharge ripple and improve start up operation.
SHUTDOWN AND UNDERVOLTAGE LOCKOUT
Figure 4 shows how to add undervoltage lockout (UVLO)
to the LT1767. Typically, UVLO is used in situations where
the input supply is current limited , or has a relatively high
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
load to the source and can cause the source to current limit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where these problems might occur.
An internal comparator will force the part into shutdown
below the minimum V
to prevent excessive discharge of battery-operated sys-
tems. If an adjustable UVLO threshold is required, the
shutdown pin can be used. The threshold voltage of the
shutdown pin comparator is 1.33V. A 3 A internal current
source defaults the open pin condition to be operating (see
Typical Performance Graphs). Current hysteresis is added
above the SHDN threshold. This can be used to set voltage
hysteresis of the UVLO using the following:
10
APPLICATIONS
V
IN
C1
R2
R1
SHDN
LT1767
IN
Figure 4. Undervoltage Lockout
3 A
U
IN
1.33V
7 A
of 2.6V. This feature can be used
INFORMATION
U
GND
W
V
V
SW
CC
U
OUTPUT
+
1767 F04
Example: switching should not start until the input is
above 4.75V and is to stop if the input falls below 3.75V.
Keep the connections from the resistors to the SHDN pin
short and make sure that the interplane or surface capaci-
tance to the switching nodes are minimized. If high resis-
tor values are used, the SHDN pin should be bypassed with
a 1nF capacitor to prevent coupling problems from the
switch node.
SYNCHRONIZATION
The SYNC pin, is used to synchronize the internal oscilla-
tor to an external signal. The SYNC input must pass from
a logic level low, through the maximum synchronization
threshold with a duty cycle between 20% and 80%. The
input can be driven directly from a logic level output. The
synchronizing range is equal to initial operating frequency
up to 2MHz. This means that minimum practical sync
frequency is equal to the worst-case high self-oscillating
frequency (1.5MHz), not the typical operating frequency
of 1.25MHz. Caution should be used when synchronizing
above 1.6MHz because at higher sync frequencies the
amplitude of the internal slope compensation used to
V
V
V
V
R
R
R
R
H
L
H
L
1
1
2
2
– Turn-off threshold
= 3.75V
– Turn-on threshold
= 4.75V
V
4 75
H
.
V
4 75
7
H
.
A
V
V
7
R
V
143
L
1 33
1
1 33
.
A
3 75
.
1 33
.
1 33
k
.
V
.
V
V
V
V
3
143
A
3
k
A
49 4
.
k
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