Datasheet

FB
SW
BST
VCC
ISEN
SGND
VIN
SS
RTN
GN
A2
On
Timer
Minimum
Off
Timer
Logic
Regulation
Comparator
A3
Current Limit
Detect
GND
R5
RON/SD
V
IN
C10
C5
D1
LM34919B
C8
6V to 24V
IN
B3
A1
D1
C6
0.022 PF
C1
1 PF
1 PF
0.1 PF
R1
28k
C2
2.5V
V
O
3.3V
C4
0.1 PF
C3
D3
0.022 PF
D2
B1
C1
C9
0.1 PF
L1 8.2 PH
R6 0:
R4
0:
C7
C3
R2
787:
R3
2.49k
3300
pF
7.87 k:
10 PF
10 PF
www.ti.com Monitor The Inductor Current
R5 and C10 are then chosen from standard value components to satisfy the above product. Typically C10
is 3000 to 5000 pF, and R5 is 10kΩ to 300 kΩ. C9 is chosen large compared to C10, typically 0.1 µF, see
Figure 4 and Figure 8.
Figure 4. Minimum Output Ripple Configuration
6 Monitor The Inductor Current
The inductor’s current can be monitored or viewed on a scope with a current probe. Remove R6, and
install an appropriate current loop across the two large pads where R6 was located. In this way, the
inductor’s ripple current and peak current can be accurately determined.
7 Scope Probe Adapters
Scope probe adapters are provided on this evaluation board for monitoring the waveform at the SW pin,
and at the circuit’s output (V
OUT
), without using the probe’s ground lead that can pick up noise from the
switching waveforms..
8 Minimum Load Current
The LM34919B requires a minimum load current of ≊1 mA to ensure the boost capacitor (C5) is recharged
sufficiently during each off-time. In this evaluation board, the minimum load current is provided by the
feedback resistors allowing the board’s minimum load current at V
OUT
to be specified at zero.
5
SNVA418A–May 2010–Revised April 2013 AN-2016 LM34919B Evaluation Board
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