FN4496 Datasheet, PDF (9/14 Pages) Intersil Corporation – Advanced PWM and Dual Linear Power Control

HIP6017
For an equation for the output inductor ripple current see the
section under component guidelines titled ‘Output Inductor
Selection’.
OVER-CURRENT TRIP: V_DS > V_SET
(i_D x r_DS(ON) > I_OCSET • R_OCSET)
OCSET
I_OCSET
200µA
VCC
DRIVE
OC1
+
-
OVER-
CURRENT1
PWM
HIP6017
GATE
CONTROL
UGATE
PHASE
VCC
LGATE
PGND
V_IN = +5V
R_OCSET
V_SET ⁺
i_D
+
V_DS
V_PHASE = V_IN - V_DS
V_OCSET = V_IN - V_SET
FIGURE 9. OVER-CURRENT DETECTION
OUT1 Voltage Program
The output voltage of the PWM converter is programmed to
discrete levels between 1.8V_DC and 3.5V_DC . This output is
designed to supply the microprocessor core voltage. The
voltage identification (VID) pins program an internal voltage
reference (DACOUT) through a TTL-compatible 5-bit
digital-to-analog converter. The level of DACOUT also sets
the PGOOD and OVP thresholds. Table 1 specifies the
DACOUT voltage for the different combinations of
connections on the VID pins. The VID pins can be left open
for a logic 1 input, because they are internally pulled up to
+5V by a 10µA (typically) current source. Changing the VID
inputs during operation is not recommended. The sudden
change in the resulting reference voltage could toggle the
PGOOD signal and exercise the over-voltage protection.
All VID pin combinations resulting in an INHIBIT disable the
IC and the open-collector at the PGOOD pin.
Application Guidelines
Soft-Start Interval
Initially, the soft-start function clamps the error amplifier’s
output of the PWM converter. After the output voltage
increases to approximately 80% of the set value, the
reference input of the error amplifier is clamped to a voltage
proportional to the SS pin voltage. Both linear outputs follow
a similar start-up sequence. The resulting output voltage
sequence is shown in Figure 6.
The soft-start function controls the output voltage rate of rise
to limit the current surge at start-up. The soft-start interval is
programmed by the soft-start capacitor, C_SS. Programming
a faster soft-start interval increases the peak surge current.
The peak surge current occurs during the initial output
voltage rise to 80% of the set value.
Shutdown
The PWM output does not switch until the soft-start voltage
(V_SS) exceeds the oscillator’s valley voltage. Additionally,
the reference on each linear’s amplifier is clamped to the
soft-start voltage. Holding the SS pin low with an open drain
or collector signal turns off all three regulators.
The VID codes resulting in an INHIBIT as shown in Table 1
also shuts down the IC.
VID4
0
0
0
TABLE 1. V_OUT1 VOLTAGE PROGRAM
PIN NAME
VID3
VID2
VID1
VID0
NOMINAL
OUT1
VOLTAGE
DACOUT
1
X
X
X
INHIBIT
0
1
1
X
INHIBIT
0
1
0
1
1.80
0
0
1
0
0
1.85
0
0
0
1
1
1.90
0
0
0
1
0
1.95
0
0
0
0
1
2.00
0
0
0
0
0
2.05
1
1
1
1
1
INHIBIT
1
1
1
1
0
2.1
1
1
1
0
1
2.2
1
1
1
0
0
2.3
1
1
0
1
1
2.4
1
1
0
1
0
2.5
1
1
0
0
1
2.6
1
1
0
0
0
2.7
1
0
1
1
1
2.8
1
0
1
1
0
2.9
1
0
1
0
1
3.0
1
0
1
0
0
3.1
1
0
0
1
1
3.2
1
0
0
1
0
3.3
1
0
0
0
1
3.4
1
0
0
0
0
3.5
NOTE: 0 = connected to GND or V_SS, 1 = open or connected to 5V
through pull-up resistors, X = don’t care
Layout Considerations
MOSFETs switch very fast and efficiently. The speed with
which the current transitions from one device to another
causes voltage spikes across the interconnecting
impedances and parasitic circuit elements. The voltage
spikes can degrade efficiency, radiate noise into the circuit,
and lead to device over-voltage stress. Careful component
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