LT3689EMSE#PBF Linear Technology, LT3689EMSE#PBF Datasheet - Page 25

• Manufacturer Part Number: LT3689EMSE#PBF
• Description: IC SWIT REG BUCK 700MA ADJ 16MSO
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3689EMSE#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 34.2 V
• Current - Output: 700mA
• Frequency - Switching: 350kHz ~ 2.2MHz
• Voltage - Input: 3.6 ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-MSOP Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
is limited by the largest available low leakage capacitor.
The accuracy of the timeout period will be affected by
capacitor leakage (the nominal charging current is 2µA)
and capacitor tolerance. A low leakage ceramic capacitor
is recommended.
Selecting the Watchdog Timing Capacitor
The watchdog timeout period is adjustable and can be
optimized for software execution. The watchdog upper
boundary timeout period, t
ing a capacitor, C
Given a specified watchdog timeout period, the capacitor
is determined by:
This equation is accurate for upper boundary periods of
20ms, or greater. The watchdog lower boundary period
(t
tor. The t
In addition, the following equation can be used to calculate
the watchdog lower boundary period for a given C
capacitor value.
These lower boundary period equations are accurate for a
t
periods, see the Watchdog Upper and Lower Boundary
Periods vs Capacitance graphs in the Typical Performance
Characteristics section.
Leaving the C
watchdog timeout of approximately 200µs. Maximum
timeout is limited by the largest available low leakage
capacitor. The accuracy of the timeout period will be af-
fected by capacitor leakage (the nominal charging current
is 2µA) and capacitor tolerance. A low leakage ceramic
capacitor is recommended.
WDL
WDL
C
C
t
WDL
WDT
WDT
of 3ms, or greater. To program faster t
) has a fixed relationship to t
WDL
=
= t
= t
31
1
WDT
WDU
WDL
period is related to t
• t
WDT
pin unconnected will generate a minimum
WDU
• 55
•
1.7nF
, between the C
ms
ms
pF
WDU
is adjusted by connect-
WDU
WDU
WDT
for a given capaci-
by the following:
pin and ground.
WDU
and t
WDT
WDL
Shorted and Reversed Input Protection
If an inductor is chosen to prevent excessive saturation,
the LT3689 will tolerate a shorted output. When operat-
ing in short-circuit condition, the LT3689 will reduce
its frequency until the valley current is at a typical value of
1.2A (see Figure 13). There is another situation to consider
in systems where the output will be held high when the
input to the LT3689 is absent. This may occur in battery
charging applications or in battery backup systems where
a battery or some other supply is diode ORed with the
Figure 13. The LT3689 Reduces its Frequency to Below
100kHz to Protect Against Shorted Output with 36V Input
Figure 14. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output; It Also
Protects the Circuit from a Reversed Input. The LT3689
Runs Only When the Input Is Present
V
IN
0.5A/DIV
20V/DIV
V
SW
I
L
V
EN/UVLO
IN
LT3689
GND
OUT
LT3689/LT3689-5
10µs/DIV
BST
SW
DA
FB
3689 F13
+
3689 F14
V
OUT
25
3689fd