LM34910_15 Datasheet, PDF (2/18 Pages) Texas Instruments – High Voltage (40V, 1.25A) Step Down Switching Regulator

LM34910
SNVS297B – OCTOBER 2004 – REVISED MARCH 2013
Typical Application Circuit and Block Diagram
8V-36V
Input
10 ^VIN
7V SERIES
REGULATOR
LM34910
C5
C1
RON
RON/
8 SD
ON TIMER
RON _START
COMPLETE
VCC
UVLO
-
280 ns
+
OFF TIMER ^0.7V
START
COMPLETE
THERMAL
SHUTDOWN
VCC ₉
C3
BST 2
2.5V
11.5 PA
7 SS
C6
6 FB ⁺
-
REGULATION
COMPARATOR
+
-
2.875VOCVOEMR-PVAORLATTAOGRE
5 RTN
LOGIC
DRIVER
GATE DRIVE
UVLO
C4
V_IN
LEVEL
SHIFT
DRIVER
L1
SW 1
CURRENT LIMIT
COMPARATOR
+
-
-
62.5 mV ₊
D1
ISEN 3
R1
RSENSE
50 m:
SGND ₄
R2
VOUT1
R3
VOUT2
C2
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PIN DESCRIPTIONS
PIN
NAME
DESCRIPTION
APPLICATION INFORMATION
1
SW
Switching Node
Internally connected to the buck switch source. Connect to
the external inductor, diode, and boost capacitor.
2
BST
Boost pin for boot-strap capacitor
Connect a 0.022 µF capacitor from SW to this pin. An
internal diode charges the capacitor during the off-time.
3
I_SEN
Current sense input
Internally the current sense resistor connects from this pin to
S_GND. Re-circulating current flows out of this pin to the free-
wheeling diode. Current limit is set at 1.25A.
4
S_GND
Sense Ground
Re-circulating current flows into this pin to the current sense
resistor.
5
RTN
Circuit Ground
Ground for all internal circuitry other than the current limit
detection.
6
FB
Feedback
Internally connected to the regulation and over-voltage
comparators. The regulation level is 2.5V.
7
SS
Softstart
An internal 11.5 µA current source charges an external
capacitor to 2.5V to provide the softstart function.
8
R_ON/SD
On-time Control and Shutdown
An external resistor from V_IN to this pin sets the buck switch
on-time. Grounding this pin shuts down the regulator.
Nominally regulated to 7.0V. An external voltage (8V-14V)
9
V_CC
Output from the start-up regulator
can be connected to this pin to reduce internal dissipation.
An internal diode connects V_CC to V_IN.
10
V_IN
Input supply voltage
Nominal input range is 8.0V to 36V.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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