NCP1587 ONSEMI [ON Semiconductor], NCP1587 Datasheet - Page 6

• Manufacturer Part Number: NCP1587
• Description: Low Voltage Synchronous Buck Controller
• Manufacturer: ONSEMI [ON Semiconductor]

General
intended for DC−DC conversion from 5.0 V & 12 V buses.
The devices have a 1 A internal gate driver circuit designed
to drive N−channel MOSFETs in a synchronous−rectifier
buck topology. The output voltage of the converter can be
precisely regulated down to 800 mV ±1.0% when the V
pin is tied to V
to 275 kHz (NCP1587) and 200 kHz (NCP1587A). A high
gain operational transconductance error amplifier (OTA) is
used.
Duty Cycle and Maximum Pulse Width Limits
at an operating point defined by the ratio of the input to the
output voltage. The devices can achieve an 80% duty cycle.
There is a built in off−time which ensures that the bootstrap
supply is charged every cycle. Both parts can allow a 12 V
to 0.8 V conversion at 275 kHz (NCP1587) and 200 kHz
(NCP1587A).
Input Voltage Range (V
13.2 V with respect to GND and PHASE, respectively.
Although BST is rated at 13.2 V with respect to PHASE, it
can also tolerate 26.4 V with respect to GND.
The NCP1587 and NCP1587A are PWM controllers
In steady state DC operation, the duty cycle will stabilize
The input voltage range for both V
Comp
V
V
BG
TG
V
CC
out
fb
OUT
POR
. The switching frequency, is internally set
4.2 V
CC
Program
550 mV
50 mV
UVLO
and BST)
OCP
ming
0.9 V
CC
DETAILED OPERATING DESCRIPTION
and BST is 4.5 V to
Figure 8. Soft−Start Implementation
SS
http://onsemi.com
FB
6
External Enable/Disable
below the 400 mV threshold, it disables the PWM Logic and
the gate drive outputs. In this disabled mode, the operational
transconductance amplifier (EOTA) output source current is
reduced and limited to the Soft−Start mode of 10 mA.
Normal Shutdown Behavior
because the input supply reaches UVLO threshold. In this
case, switching stops, the internal SS is discharged, and all
GATE pins go low. The switch node enters a high impedance
state and the output capacitors discharge through the load
with no ringing on the output voltage.
External Soft−Start
which reduces inrush current and overshoot of the output
voltage. Soft−start is achieved by using the internal current
source of 10 mA (typ), which charges the external integrator
capacitor of the transconductance amplifier. Figure 8 is a
typical soft−start sequence. This sequence begins once V
surpasses its UVLO threshold and OCP programming is
complete. During soft−start, as the Comp Pin rises through
400 mV, the PWM Logic and gate drives are enabled. When
the feedback voltage crosses 800 mV, the EOTA will be
given control to switch to its higher regulation mode output
current of 120 mA.
NORMAL
When the Comp pin voltage falls or is pulled externally
Normal shutdown occurs when the IC stops switching
The NCP1587/A features an external soft−start function,
0.8 V
CC