ncp1589l ON Semiconductor, ncp1589l Datasheet - Page 7

• Manufacturer Part Number: ncp1589l
• Description: Ncp1589l Low Voltage Synchronous Buck Controller With Light Load Efficiency And Transient Enhancement
• Manufacturer: ON Semiconductor

conduction mode. The output frequency can be determined
by the following equation:
F
k1 = 1, k2 = 0, Ramp_slope = 0.5 V/ms, V
V
Light Load Operation
frequency of the NCP1589L is almost constant. In light load,
it runs in a discontinuous current mode with a scaled-down
frequency as a function of the load current. Internal zero
current detection threshold will change adaptively to ensure
SW
offset
PGOOD
Internal
Where k1, k2 is an internal trimmed value; by default,
In continuous current conduction mode, the operating
COMP
UVLO
Fault
VCC
V
+
UG
OUT
LG
= 20 mV.
FB
V
out
V
POR
R10)R9
k1
in
R9
4.4 V
Ramp_slope
Programming Time
V
ramp
OCP
1.3 V
) V
offset
Soft−Start Time
ramp
Figure 4. Typical Startup Sequence
1 ) k2
1
= 1.5 V,
(eq. 2)
http://onsemi.com
V
V
out
in
NORMAL
7
0.8 V
the minimum amount of diode conduction period to further
reduce the converter power consumption in the light load
condition.
Feedback Voltage
from 0.8 V to 5 V via an external resistor divider network
(R1, R4 in Figure 1). The controller will try to maintain
0.8 V at the FB pin. Thus, if a resistor divider circuit was
placed across the feedback pin to V
regulate the output voltage in proportion to the resistor
divider ratio in order to maintain 0.8 V at the FB pin. The
relation between the resistor divider network and the output
voltage is show in the following equation:
R4 + R1
The NCP1589L allows the output voltage to be adjusted
V
out
V
* V
ref
ref
+ R1
4.0 V
out
V
, the controller will
out
0.8 V
* 0.8 V
(eq. 3)