AN938 Datasheet, PDF (31/33 Pages) STMicroelectronics – The L4973 family is a 3.5 A monolithic DC-DC converter

AN938
Applications
In inverting buck-boost topology the lower voltage rail of the device floats with the negative
output voltage. The voltage applied to the device is equal to (V_IN + |V_OUT|) whose upper limit
is given by the maximum input voltage range of the device (55 V).
Figure 42. Negative output voltage
V_CC
C_IN
R_OSC
C_IN1
C_OSC
C_BOOT
L
9
2,3
7,8
L4973
4,5,6
1 ¹⁷ 13,14,15
12
11
V_FB
D
Rc
C_SS
Cc
-Vo
R₁
C_OUT
R₂
V_CCMax = 55 -⏐V_O⏐
AM03524v1
4.6
Negative boost converter
Figure 43 shows how to stabilize a negative output voltage higher than negative input
voltage.
Figure 43. Negative boost converter.
R_OSC
C_IN
OSC
C_OSC
-V_CC
|V_CC|<|V_OUT|
V_CC
7,8
12
L4973
2,3
GND
V_FB
C_BOOT
OUT
L
C_OUT
D
R₁
R₂
8V≤|V_OUT|≤55V
AM03525v1
Doc ID 5410 Rev 10
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