ISL6567_07 Datasheet, PDF (14/26 Pages) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

ISL6567
VCC
ISL6567
I_H
(10μA)
EXTERNAL CIRCUIT
VDIFF
+
MON
-
COMPARATOR
+
V_REF
(300mV) ^-
MON
R_S
R_P
FIGURE 11. SETTING THE MONITORING THRESHOLD AND
HYSTERESIS
While in external reference (ER) mode, the threshold
sensitive MON pin can be used to control when the ISL6567
starts to monitor the output for PGOOD and OVP protection
purposes. As shown in Figure 11, connect the MON pin to
the voltage to be monitored via a resistor divider. An internal
current source helps set a user-adjustable monitor threshold
hysteresis. Choose resistor values according to desired
hysteresis voltage, V_H, and desired rising threshold, V_T.
R_S
=
V_-----H--
I_H
R_P
=
-^R-----^S-----^â‹---^V----^R----^E----^F--
V_T – V_REF
Make note that, in these equations, V_REF refers to the
reference of the MON comparator (300mV).
Intersil recommends the MON threshold is set to be tripped
when the external reference voltage reaches at least 90% of
the final DC value. Since PGOOD and OVP monitoring are
relative to the external reference magnitude, it is important to
understand that the PGOOD and OVP thresholds will move
in proportion to the moving reference (externally soft-started
reference). Thus, the absolute thresholds of PGOOD and
OVP
ISL6567 POWER-GOOD OPERATION
The open-collector PGOOD output reports on the quality of
the regulated output voltage. Once the ISL6567 is enabled
and the MON pin is above its threshold, PGOOD goes open
circuit when the output enters the power-good window (see
Electrical Specifications), and stays open for as long as the
output remains within the specified window. The PGOOD is
immediately pulled low if the ISL6567 is disabled by removal
of bias, toggling of the EN pin, or upon encountering of an
overcurrent event; PGOOD is allowed to report the status of
the output as soon as operation is resumed following any of
these events.
V_TARGET
V_OUT
REFTRK
+
To V_{TARGET RS}
R_P
ISL6567
V_REF
EXT CIRCUIT
+
E/A
-
FB
R₁
VDIFF
------^V----^O-----^U----^T-------
V_TARGET
=
--------^R----^P---------
R_P + R_S
+
X1
-
VSEN
RGND
-
+
To V_OUT
FIGURE 12. RATIOMETRIC VOLTAGE TRACKING
The MON pin is used in external-reference configurations,
where the reference is controlled by a circuit external to the
ISL6567. As such, the ISL6567 has no way of ‘knowing’
when the external reference has stabilized to its full value, or
is within a certain percentage of its final value. Thus, the
MON pin’s functionality can be used to indicate when a
desired threshold has been reached (either by monitoring
the reference itself, or the output voltage controlled by the
ISL6567). By default, when operating in external-reference
mode and desiring PGOOD monitoring as shown in this
datasheet, it is recommended the MON is set to trip its
threshold when the output voltage (or reference) reaches
92% of the final set value, choosing the resistor divider as to
achieve a 2% hysteresis.
When operating in internal-reference mode, the value of the
reference is known to the ISL6567, so the MON pin function
can be bypassed by tying it to VCC potential.
VOLTAGE TRACKING AND SEQUENCING
By making creative use of the reference clamps at the SS
and REFTRK pins, and/or the available external reference
input, as well as the functionality of the EN pin, the ISL6567
can accommodate the full spectrum of tracking and
sequencing options. The following figures offer some
implementation suggestions for a few typical situations.
14
FN9243.2
March 20, 2007