ADP-I2C-USB-Z View Datasheet(PDF) - Analog Devices
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ADP-I2C-USB-Z Datasheet PDF : 108 Pages
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Data Sheet
CONSTANT CURRENT MODE
Constant current mode is part of the PMBus output current
fault response function. When the output current reaches the
IOUT_OC_FAULT_LIMIT value, the ADP1051 can be
configured to operate in constant current mode, using the
output current as the feedback signal for closed-loop operation
(see Figure 31). To ensure that the output current remains constant,
the output voltage is ramped down linearly as the load resistance
decreases.
VOUT
VOUT NOMINAL
IOUT_OC_FAULT_LIMIT
(REG 0x46)
IOUT NOMINAL
IOUT
Figure 31. Constant Current Mode (VOUT vs. IOUT)
Two CS2 output current averaging speeds can be selected via
Register 0xFE1B[4]: a 9-bit CS2 current averaging speed and
a 7-bit CS2 current averaging speed. The 9-bit CS2 current
averaging speed has a VS basic voltage change rate of 1.18 mV/ms.
The 7-bit CS2 current averaging speed has a VS basic voltage
change rate of 4.72 mV/ms. In addition, the output voltage change
rate can be set by Register 0xFE3A[7:6] to 1×, 2×, 4×, or 8× the
VS± basic voltage change rate.
PULSE SKIPPING
The pulse skipping function can reduce the switching loss under
very light load current conditions while keeping the output voltage
stable. Register 0xFE67[6] can be set to activate this function.
When light load mode or deep light load mode is enabled, as the
output current drops, the supply enters discontinuous conduction
mode (DCM). In DCM, the modulation value is a function of the
load current. If a very light load current requires a modulation
value (duty cycle) of less than the threshold set by Register 0xFE69,
pulse skipping mode is enabled. In pulse skipping mode, the PWM
output appears intermittently. If the digital compensator signals
an error requiring a modulation value that is less than the threshold
set by Register 0xFE69, no PWM pulses are generated. If the digital
compensator signals an error requiring a modulation value that is
greater than the threshold set by Register 0xFE69, PWM pulses
are generated.
The pulse skipping mode is always blanked during soft start.
ADP1051
PRE-BIAS STARTUP
The pre-bias start-up function provides the capability to start up
with a pre-biased voltage on the output. It protects the power
supply against existing external voltage on the output during
startup and ensures a monotonic startup before the power supply
reaches full regulation (see Figure 32).
PSON
VOUT
0V
PWM
OUTPUTS
Figure 32. Pre-Bias Startup
The pre-bias start-up function is enabled by Register 0xFE25[7].
During pre-bias startup, the ADP1051 soft start ramp starts at
the existing voltage value sensed on the VS± pins, and the soft
start ramp time is reduced proportionally. The initial PWM
modulation value does not begin with zero but, instead, with
a value that builds a balanced relationship between the input
voltage and the output voltage. This balance avoids the sudden
charging or discharging of the output capacitor and achieves
a monotonic and smooth startup. The initial modulation value
is calculated by the following equation:
t MODU _ INI
= t MODU _ NOM
× VOUT
VOUT _ NOM
× VIN _ NOM
V IN
where:
tMODU_INI is the initial modulation value when the controller begins
to generate PWM pulses during startup.
tMODU_NOM is the modulation value set by Register 0xFE39. It
emulates the modulation value when the input voltage and the
output voltage are in the nominal condition.
VOUT is the sensed output voltage.
VOUT_NOM is the nominal output voltage set by VOUT_COMMAND
(Register 0x21).
VIN_NOM is the nominal input voltage when the VF pin voltage = 1 V.
VIN is the sensed input voltage.
In addition, Register 0xFE6C[1] is set for correct operation. To
sense the input voltage (represented by VF) when the power supply
is off, use additional circuitry, such as an auxiliary power circuit,
to sense the input voltage.
If the input voltage signal is not available when the power is off,
the tMODU_INI value is calculated based on the tMODU_NOM and the
output voltage information. In this case, Register 0xFE6C[1]
is cleared to 0.
Rev. B | Page 27 of 108
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