ISL78229
Functional Pin Description(Continued)
PIN NAME
PIN #
DESCRIPTION
IMON
5
The average current monitor pin for the sum of the two phases’ inductor currents. It is used for average current limiting and
average current protection functions.
The sourcing current from the IMON pin is the sum of the two CSA’s outputs plus a fixed 17µA offset current. With each CSA
sensing individual phase’s inductor current, the IMON signal represents the sum of the two phases’ inductor currents and is
the input current for the boost. Place a resistor in parallel with a capacitor from IMON to ground. The IMON pin output current
signal builds up the average voltage signal representing the average current sense signals.
A constant average current limiting function and an average current protection are implemented based on the IMON signal.
1. Constant Average Current Limiting: A Constant Current (CC) control loop is implemented to limit the IMON average
current signal using a 1.6V reference, which ultimately limits the total input average current to a constant level.
2. Average Current Protection: If the IMON pin voltage is higher than 2V, the part will go into either Hiccup or Latch-off fault
protection as described in “Fault Response Register SET_FAULT_RESPONSE (D2h)” on page 35.
Refer to “Average Current Sense for 2 Phases - IMON” on page 33 for more details.
TRACK
6
External reference input pin for the IC output voltage regulation loop to follow. The input reference signal can be either a digital
or analog signal selected by the ATRK/DTRK pin configuration.
If the TRACK function is not used, connect the TRACK pin to VCC and the internal VREF_DAC will work as the reference. Refer
to “Digital/Analog TRACK Function” on page 26 for more details.
ADDR1
ADDR2
PGOOD
7
8
9
ADDR1, a logic input in combination with ADDR2, selects one of four bus addresses. Refer to “Device Identification
Address and Read/Write” on page 43 for more details.
ADDR2, a logic input in combination with ADDR1, selects one of four bus addresses. Refer to “Device Identification
Address and Read/Write” on page 43 for more details.
Provides an open-drain power-good signal. Pull up this pin with a resistor to this IC’s VCC for proper function. When the output
voltage is within OV/UV thresholds and soft-start is completed, the internal PGOOD open-drain transistor is open and PGOOD
is pulled HIGH. It will be pulled low once output UV/OV or input OV conditions are detected. Refer to “PGOOD Signal” on
page 31 for more details.
FSYNC
10
A dual-function pin for switching frequency setting and synchronization defined as follows:
1. The PWM switching frequency can be programmed by a resistor R
from this pin to ground. The PWM frequency
FSYNC
refers to a single-phase switching frequency in this datasheet. The typical programmable frequency range is 50kHz
to 1.1MHz.
2. The PWM switching frequency can also be synchronized to an external clock applied on the FSYNC pin. The FSYNC
pin detects the input clock signal’s rising edge to be synchronized with. The typical detectable minimum pulse width
of the input clock is 20ns. The rising edge of LG1 is delayed by 35ns from the rising edge of the input clock signal
at the FSYNC pin. Once the internal clock is locked to the external clock, it will latch to the external clock. If the
external clock on the FSYNC pin is removed, the switching frequency oscillator will shut down. The part will then
detect PLL_LOCK fault and go to either Hiccup mode or Latch-off mode as described in “Fault Response Register
SET_FAULT_RESPONSE (D2h)” on page 35. If the part is set in Hiccup mode, the part will restart with the frequency
set by R
.
FSYNC
SGND
11
Signal ground pin that the internal sensitive analog circuits refer to. Connect this pin to a large copper ground plane free
from large noisy signals. In layout power flow planning, avoid having the noisy high frequency pulse current flowing
through the ground area around the IC.
SDA
SCL
12
13
14
Serial bus data input/output. Requires pull-up.
Serial bus clock input. Requires pull-up.
SALERT
PMBus Alert Output. An open-drain output that is pulled low when a fault condition is detected. Requires pull-up. Refer to “Fault
Flag Register FAULT_STATUS (D0h) and SALERT Signal” on page 35 for more details.
NTC
15
External temperature sensor input. An NTC resistor from this pin to GND can be used as the external temperature sensing
component. A 20µA current sources out of this pin. The voltage at this pin is 20µA times the NTC resistor, which
represents the temperature. The voltage on this pin is converted by the internal ADC and stored in the NTC register which
can be read over the PMBus. Refer to “External Temperature Monitoring and Protection (NTC Pin)” on page 38 for more
details.
DE/PHDRP
RBLANK
16
17
Used to select Diode Emulation mode (DE), Phase Dropping (PH_DROP) mode, or Continuous Conduction Mode (CCM). There
are 3 configurable modes: 1. DE mode; 2. DE plus PH_DROP mode; 3. CCM mode.
Refer to Table 2 on page 34 for the three configurable options.
The phase dropping mode is not allowed with external synchronization.
A resistor from this pin to ground programs the blanking time for current sensing after the PWM is ON (LG is ON). This
blanking time is also called t
time, meaning the minimum ON-time once a PWM pulse is ON. Refer to “Minimum
MINON
On-Time (Blank Time) Consideration” on page 30 for information about R
.
BLANK
FN8656 Rev.5.00
Sep 18, 2017
Page 4 of 73
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