LM34919_14 Datasheet, PDF (2/21 Pages) Texas Instruments – Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator

LM34919
SNOSAY2D – MAY 2007 – REVISED JUNE 2008
Connection Diagram
SW
VIN D1
D2
D3
BST
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D3
D2
D1
ISEN C1
C3
VCC
C3
C1
SGND ^B1
B3
SS
B3
B1
RON/SD A1
A2
A3
FB
RTN
Figure 1. Bump Side
A3
A2
A1
Figure 2. Top View
Pin Functions
Pin No.
A1
A2
A3
B1
B3
C1
C3
D1
D2
D3
Name
RON/SD
RTN
FB
SGND
SS
ISEN
VCC
VIN
SW
BST
Table 1. Pin Descriptions
Description
Application Information
On-time control and
shutdown
An external resistor from VIN to this pin sets the buck switch on-time.
Grounding this pin shuts down the regulator.
Circuit Ground
Ground for all internal circuitry other than the current limit detection.
Feedback input from the Internally connected to the regulation and over-voltage comparators. The
regulated output
regulation level is 2.5V.
Sense Ground
Re-circulating current flows into this pin to the current sense resistor.
Softstart
An internal current source charges an external capacitor to 2.5V, providing
the softstart function.
Current sense
The re-circulating current flows through the internal sense resistor, and out of
this pin to the free-wheeling diode. Current limit is nominally set at 0.64A.
Output from the startup Nominally regulates at 7.0V. An external voltage (7V-14V) can be applied to
regulator
this pin to reduce internal dissipation. An internal diode connects VCC to VIN.
Input supply voltage
Nominal input range is 8.0V to 40V.
Switching Node
Internally connected to the buck switch source. Connect to the inductor, free-
wheeling diode, and bootstrap capacitor.
Boost pin for bootstrap Connect a 0.022 µF capacitor from SW to this pin. The capacitor is charged
capacitor
from V_CC via an internal diode during each off-time.
2
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