Datasheet

NCP1422
http://onsemi.com
8
TYPICAL OPERATING CHARACTERISTICS
50
60
70
80
90
100
1 10 100 1000
NCP1422
V
OUT
= 1.8 V
L = 6.8 H
C
IN
= 22 F
C
OUT
= 22 F
T
A
= 25_C
OUTPUT LOADING CURRENT, I
OUT
/mA
EFFICIENCY/%
50
60
70
80
90
100
1 10 100 1000
NCP1422
V
OUT
= 3.3 V
L = 6.8 H
C
IN
= 22 F
C
OUT
= 22 F
T
A
= 25_C
OUTPUT LOADING CURRENT, I
OUT
/mA
EFFICIENCY/%
50
60
70
80
90
100
1 10 100 1000
Figure 20. Efficiency vs. Load Current
Figure 21. Efficiency vs. Load Current
Figure 22. Efficiency vs. Load Current
NCP1422
V
OUT
= 5.0 V
L = 6.8 H
C
IN
= 22 F
C
OUT
= 22 F
T
A
= 25_C
OUTPUT LOADING CURRENT, I
OUT
/mA
EFFICIENCY/%
V
IN
= 2.5 V
V
IN
= 1.5 V
V
IN
= 2.0 V
V
IN
= 3.3 V
V
IN
= 1.5 V
V
IN
= 2.5 V
V
IN
= 1.5 V
V
IN
= 1.2 V
DETAILED OPERATION DESCRIPTION
NCP1422 is a monolithic micropower high−frequency
step−up voltage switching converter IC specially designed
for battery operated hand−held electronic products up to
800 mA loading. It integrates a Synchronous Rectifier to
improve efficiency as well as to eliminate the external
Schottky diode. High switching frequency (up to 1.2 MHz)
allows for a low profile inductor and output capacitor to be
used. Low−Battery Detector, Logic−Controlled Shutdown,
and Cycle−by−Cycle Current Limit provide value−added
features for various battery−operated applications. With all
these functions ON, the quiescent supply current is
typically only 8.5 A. This device is available in a compact
DFN−10 package.
PFM Regulation Scheme
From the simplified functional diagram (Figure 1), the
output voltage is divided down and fed back to pin 1 (FB).
This voltage goes to the non−inverting input of the PFM
comparator whereas the comparator’s inverting input is
connected to the internal voltage reference, REF. A
switching cycle is initiated by the falling edge of the
comparator, at the moment the main switch (M1) is turned
ON. After the maximum ON−time (typically 0.72 S)
elapses or the current limit is reached, M1 is turned OFF
and the synchronous switch (M2) is turned ON. The M1
OFF time is not less than the minimum OFF−time
(typically 0.12 S), which ensures complete energy