LT1766EGN#TR Linear Technology, LT1766EGN#TR Datasheet - Page 17

• Manufacturer Part Number: LT1766EGN#TR
• Description: IC SW REG STP-DWN 200KHZ 16-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1766EGN#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 54 V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LT1766EGNTR

APPLICATIONS INFORMATION
BOOST PIN
For most applications, the boost components are a 0.33μF
capacitor and a 1N4148W diode. The anode is typically
connected to the regulated output voltage to generate a
voltage approximately V
stage. However, the output stage discharges the boost ca-
pacitor during the on time of the switch. The output driver
requires at least 3V of headroom throughout this period
to keep the switch fully saturated. If the output voltage is
less than 3.3V, it is recommended that an alternate boost
supply is used. The boost diode can be connected to the
input, although, care must be taken to prevent the 2× V
boost voltage from exceeding the BOOST pin absolute
maximum rating. The additional voltage across the switch
driver also increases power loss, reducing effi ciency. If
available, and independent supply can be used with a local
bypass capacitor.
A 0.33μF boost capacitor is recommended for most ap-
plications. Almost any type of fi lm or ceramic capacitor
is suitable, but the ESR should be <1Ω to ensure it can
be fully recharged during the off time of the switch. The
capacitor value is derived from worst-case conditions of
4700ns on time, 42mA boost current and 0.7V discharge
ripple. The boost capacitor value could be reduced under
less demanding conditions, but this will not improve cir-
cuit operation or effi ciency. Under low input voltage and
low load conditions, a higher value capacitor will reduce
discharge ripple and improve start-up operation.
INPUT
C2
OUT
R
R
LO
HI
above V
IN
SHDN
IN
LT1766
to drive the output
Figure 4. Undervoltage Lockout
5.5μA
2.38V
0.4V
IN
GND
R
FB
+
–
+
–
SHUTDOWN FUNCTION AND UNDERVOLTAGE
LOCKOUT
Figure 4 shows how to add undervoltage lockout (UVLO)
to the LT1766. 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.
Threshold voltage for lockout is about 2.38V. A 5.5μA
bias current fl ows out of the pin at this threshold. The
internally generated current is used to force a default high
state on the shutdown pin if the pin is left open. When
low shutdown current is not an issue, the error due to this
current can be minimized by making R
shutdown current is an issue, R
but the error due to initial bias current and changes with
temperature should be considered.
V
R
R
IN
LO
HI
= Minimum input voltage
=
=
2 38
10
.
R
k
LO
STANDBY
TOTAL
SHUTDOWN
to 100k 25k suggested
V R
(
V
−
IN
−
LO
V
2 38
SW
(
(
.
5 5
LT1766/LT1766-5
. μ
V
)
A
L1
)
LO
+
can be raised to 100k,
1766 F04
C1
)
OUTPUT
LO
10k or less. If
17
1766fc