CALIFORNIA MICRO DEVICES
CMPWR300
Typical Transient Characteristics
During a selection or deselection transition the DC load current
The transient characterization test setup shown below includes
the effective source impedance of the VCC supply (RS). This
was measured to be approximately 0.2Ω. It is recommended
that this effective source impedance be no greater than 0.25Ω
to ensure precise switching is maintained during VCC selection
and deselection.
is switching from VAUX to VCC and vice versa, or from VSBY to
VCC. In addition to the normal load current there may also
be an in-rush current for charging/discharging the load
capacitor. The total current pulse being applied to either
VAUX or VCC is equal to the sum of the dc load and the
corresponding in-rush current. Transient currents in excess
of one amp can readily occur for brief intervals when either
supply commences to power the load.
Both the rise and fall times during VCC power-up/down
sequencing were controlled to be around 10 millisecond
duration. This is considered to represent worst case conditions
for most application circuits.
The oscilloscope traces of VCC power-up/down show the full
bandwidth response at the VCC and VOUT pins under full load
(500mA) conditions.
A maximum rated load current of 500mA was used during
characterization, unless specified otherwise.
See Application note AP-211 for more details.
Cold Start and Full Power Down (Fig 2.1 to 2.6)
Cold start power up and power down from VCC, VSBY and
VAUX. The output voltage follows the input very smoothly
with no disturbance. As soon as the VCC orVSBY input voltage
reaches about 2V, VOUT starts rising. It reaches 3.3V when
VCC orVSBY equals 3.8V. VOUT remains valid until VCC orVSBY
drops below 3.8V.
This is due to the in-rush current during the power switching.
The built-in hysteresis of 300mV ensures the regulator
remains turned on throughout the transient.
Load and Line Transient Response (Fig 2.13 to 2.16)
The load transient response shows a 5mA to 500mA step
load with minimal disturbance on VOUT of 80mV. An initial
transient overshoot of 80mV occurs and the output settles
to its final voltage within a few microseconds. The dc voltage
disturbance on the output is approximately 25mV, which
demonstrates the regulator output impedance of 50mW.
The line step response shows a small disturbance of 25mV
on the output when VCC steps from 4.5V to 5.5V. When
falling from 5.5V to 4.5V, the output is almost unchanged
VCC Power Changeover (Fig 2.7 to 2.12)
Power transitions between the main VCC and the standby or
the auxiliary sources under 375mA load. The transition
between VCC and VSBY shows a small disturbance of 80mV
on VOUT
.
Transitions between VCC and VAUX show a disturbance of
about 120mV on VOUT. During power up condition, VCC
experiences 100mV disturbance.
©2000 California Micro Devices Corp. All rights reserved.
12/5/2000
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
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CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
