ISL6534CRZ Intersil, ISL6534CRZ Datasheet - Page 14

• Manufacturer Part Number: ISL6534CRZ
• Description: IC CTRLR PWM DUAL LINEAR 32QFN
• Manufacturer: Intersil

Specifications of ISL6534CRZ

• Topology: Step-Down (Buck) Synchronous (2), Linear (LDO) (1)
• Function: Any Function
• Number Of Outputs: 3
• Frequency - Switching: 300kHz ~ 1MHz
• Voltage/current - Output 1: Controller
• Voltage/current - Output 2: Controller
• Voltage/current - Output 3: Controller
• W/led Driver: No
• W/supervisor: No
• W/sequencer: Yes
• Voltage - Supply: 3.3 V ~ 12 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Once the power is “Good”, PGOOD will pull low if any of the
3 SS/EN pins is pulled low. Also, if a short is detected on
either switcher, then the PGOOD will pull low, for as long as
the condition is there. If VOUT1 or VOUT2 has a short
detected which stays there for 1-2 clock pulses, then all
three regulators will shut down, and wait for a power-down
and up cycle to reset (either VCC or VCC12 (or both) must
power down and up). If the short-circuit is not there long
enough to shut down, it may still cause PGOOD to go low
momentarily. If this causes a system issue, a filter capacitor
could be tried; it should be at least several nF to be effective.
Note that this is not a full-feature PGOOD; it is not directly
monitoring if the VOUT1 or VOUT2 drops below a set UV
level; it only checks for the simple short-circuit condition, via
the COMP pins. And it is not monitoring VOUT3 at all. So it
is a good indication that all three outputs have ramped up,
but it is less useful as a monitor from that point on.
Since PGOOD is an open-drain pull-down device, it usually
requires an external pull-up resistor; however, if the pin is not
used, no resistor is necessary. A value in the range of 1kΩ to
10kΩ is typical.
POR
Both the VCC (5V) and VCC12 (12V) are monitored for
Power-On-Reset, as shown in the Specification Table. The
two POR outputs are logically gated together, such that both
have to be above their rising trip points to enable the SS/EN
ramps to start (if they are not held low) and then enable each
output. Either POR output can go below its falling trip point to
disable all outputs, and then back to restart the enable
operation.
Shunt Regulator
The ISL6534 must have both a 12V (for VCC12) and a 5V
power supply (for VCC); both must be above their respective
POR rising trip points to enable the outputs to start
switching. The shunt regulator (nominal 5.8V) was designed
for those systems that do not have a 5V supply available; the
range of the shunt (5.6V to 6.0V) was designed not to
overlap the usual 4.75V to 5.25V range of typical power
supplies. An external resistor between VCC12 and VCC is
required; a typical value of 150Ω is the recommended
starting value (it may change due to other factors, such as
VCC12 voltage, VBS voltages, oscillator frequency, etc.).
The dissipation of the resistor is approximately 1/4W; it
needs to be sized accordingly. For example, 12V - 5.8V =
6.2V across the 150Ω resistor is 41mA; P = IV = 0.256W.
Several low-power resistors in parallel can also be used.
See Figure 11.
In either case, both VCC and VCC12 pins have small
decoupling capacitors (typically 1.0 to 10.0µF); they should
each be located near their pin, with a via to the GND plane.
14
ISL6534
Short-Circuit Protection
There is no current sensing or r
undervoltage sensing on the ISL6534. However, if either
Channel 1 or 2 output is shorted while active, there is a
simple detection on the error amp COMP output that implies
either overcurrent or undervoltage; the PGOOD pin goes low
immediately. If the condition persists for 1-2 internal clock
cycles (3-6µs at 300kHz), then ALL 3 Outputs are latched
off, requiring either a VCC or VCC12 POR to restart. The
protection was not designed to work for the case of powering
up an output into a short-circuit, and there are limitations on
detecting applied shorts. Note that the linear regulator has
no short-circuit protection.
See Application Considerations for more details.
Oscillator
The internal oscillator is nominally 300kHz (±20% tolerance)
with no external components required (tie FS_SYNC pin to
GND), as measured at either of the LG or UG pins. To run
faster, a resistor from FS_SYNC pin to GND will speed up
the frequency. See Figure 12 for a curve that shows the
frequency versus resistor value. Since the curve is steep as
it approaches 300kHz, operation in this area is not
recommended if the exact frequency is important.
Since this pin has several functions muxed onto it, it is
important that they do not interfere with each other. Thus,
the circuit that looks for the resistor will shut off (and default
to the 300kHz) if it doesn’t see a current in the expected
range. There should not be any excessive capacitive loading
on the pin either, and if a resistor is used, it should be
located very close to the FS_SYNC pin, and its connection
to GND should be near the IC GND, and away from the
output stage power GND, to minimize jitter.
FIGURE 11. SHUNT REGULATOR AND DECOUPLING
(VCC) = 5.8V
VCC PIN
VCC PIN
VCC
CAPACITORS FOR VCC AND VCC12 PINS
VCC12 PIN
VCC12 PIN
VCC12
VCC12
DS(ON)
NON-SHUNT
MODE; SEPARATE
5V AND 12V
OPTIONAL R FOR
SHUNT REGULATOR;
VCC = 5.8V
sensing or
November 18, 2005
FN9134.2