Datasheet

V
OUT
SS
RES
RT
COMP
FB
RAMP
PGND
CSG
CS
LO
SW
HO
HB
VCC
VIN
AGND
UVLO
VCCDIS
DEMB
CM
V
IN
V
OUT
SW
LM25117
C
IN
Q
H
Q
L
C
HB
D
HB
C
VCC
Hiccup Mode OVP
Triggered at 13.4V
CC Mode: 2A
100k:
15 k:
80 µF
68 µH
1500 pF
100 k:
22.1 k:
0.47 µF
3.24 k:
2.37 k:
0.022 µF
47 m:
Current Control (CC)
3.24 k:
332:
LM25117
LM25117-Q1
SNVS714E –APRIL 2011–REVISED MARCH 2013 www.ti.com
Example of Constant Current Regulator
The LM25117 can be configured as a constant current regulator by using the current monitor feature (CM) as the
feedback input. A voltage divider at the VCCDIS pin from VOUT to AGND can be used to protect against output
over-voltage. When the VCCDIS pin voltage is greater than the VCCDIS threshold, the controller disables the
VCC regulator and the VCC pin voltage decays. When the VCC pin voltage is less than the VCC UV threshold,
both HO and LO outputs stop switching. Due to the time delay required for VCC to decay below the VCC UV
threshold, the over-voltage protection operates in hiccup mode. See Figure 36.
Figure 36. Constant Current Regulator with Hiccup Mode Output OVP
The LM25117 also can be configured as a constant voltage and constant current regulator, known as CV+CC
regulator. In this configuration, there is much less variation in the current limiting as compared to peak cycle-by-
cycle current limiting of the inductor current. The LMV431 and the PNP transistor create a voltage-to-current
amplifier in the current loop. This amplifier circuitry does not affect the normal operation when the output current
is less than the current limit set-point. When the output current is greater than the set-point, the PNP transistor
sources a current into C
RAMP
and increases the positive slope of emulated inductor current ramp until the output
current is less than or equal to the current limit set-point. See Figure 37 and Figure 38.
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