Diodes AP3586A/B/C - Manual (Page 13)

Data sheet
Single Phase Synchronous Buck PWM Controller AP3586A/B/C
Mar. 2012 Rev. 1. 1 BCD Semiconductor Manufacturing Limited
13
V
IN
10V/Div
V
OUT
0.5V/Div
I
L
10A/Div
LGATE 10V/Div
Function Description (Continued)
1ms/Div
Figure 18. Soft Start Behavior of AP3586A/B/C
Power Input Detection
The AP3586A/B/C detects PHASE voltage for the
present of power input V
IN
when UGATE turns on the
first time. If the PHASE voltage does not exceed
2.0V when UGATE turns on, AP3586A/B/C asserts
that V
IN
is not ready and stops the soft start cycle.
However, the internal SS continues ramping up to
V
DD
. Another soft start is initiated after SS ramps up
to V
DD
. The hiccup period is about 1ms. Figure 19
shows the start-up waveform where V
IN
does not
present initially.
1ms/Div
Figure 19. Soft Start Where V
IN
Does Not Present
Initially
Over Current Protection (OCP)
A resistor R
OCSET
connected from LGATE pin sets the
threshold. An internal current source I
OC
(21.5 µA
typically), flowing through R
OCSET
determines the
OCP trigger point, which can be calculated using the
following equation:
Because the R
DS(ON)
of MOSFET increases with
temperature, it is necessary to take this thermal effect
into consideration in calculating OCP point.
When OCP is triggered, both UGATE and LGATE
will go low to stop the energy transfer to the load.
Controller will try to restart in a hiccupped way.
Figure 20 shows the hiccupped over current
protection. Only four times of hiccup is allowed in
over current protection. If over current condition still
exists after four times of hiccup, controller will be
latched.
Figure 20. Hiccupped Over Current Protection
Over Voltage Protection (OVP)
The feedback voltage is continuously monitored for
over voltage protection. When OVP is triggered,
LGATE will go high and UGATE will go low to
discharge the output capacitor.
The AP3586A/B/C provides full-time over voltage
protection whenever soft start completes or not. The
typical OVP threshold is 137.5% of the internal
reference voltage V
REF
. AP3586A/B/C provides
non-latched OVP. The controller will return to normal
operation if over voltage condition is removed.
Under Voltage Protection (UVP)
The feedback voltage is also monitored for under
voltage protection. The under voltage protection has
15
µs triggered delay. When UVP is triggered, both
UGATE and LGATE will go low. Unlike OCP, UVP
is not a latched protection; controller will always try
to restart in a hiccupped way.
Thermal Shutdown
If the junction temperature of the device reaches the
thermal shutdown limit of 160°C, the PWM and the
V
IN
10V/Div
V
OUT
0.5V/Div
COMP 0.5V/Div
LGATE 10V/Div
MOSFET side low the of R
R I 2
I
DS(ON)
OCSET OCSET
LIMIT
Ч Ч
=