SC4210AEVB View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC4210AEVB Datasheet PDF : 11 Pages
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SC4210A
POWER MANAGEMENT
Applications Information
Basic Operation
ILIM = 140mV ÷ RSENSE
Topology
The SC4210A incorporates a charge pump which
multiplies the input supply by a factor of approximately
three. This charge pump output, or the CAP pin, should
be bypassed to GND in order to reduce high frequency
ripple – capacitor value isn’t critical. The amplified voltage
supplies power to both the output stage of the error
amplifier and the bipolar buffer transistor which provides
the gate potential to the external N-MOSFET.
The error amplifier is a transconductance type with a
transconductance of around 0.8mSTYP. The open loop
voltage gain is about 66dB. The output of the E/A is
compensated externally through the COMP pin with an
RC series network.
The OUT pin is a buffered version of the COMP pin with
approximately 2.5kΩ output drive impedance.
Overcurrent protection is accomplished by measuring the
voltage potential between the input supply, pin VDD, and
the connection of the external sense resistor and drain
terminal of the external N-MOSFET at pin CS.
The SC4210A incorporates a UVLO rising threshold of
1.73VTYP with 90mV hysteresis.
Stability and Transient Performance
The SC4210A topology allows the device to be configured
to have both a stable performance across a wide
frequency range as well as react quickly to and recover
from transients at the output load.
Experimental and simulated results have shown that the
device performs well under the following setup conditions:
Rcomp = 24kΩ; Ccomp = 150pF
COUT = 10uF, tantalum, ESR = 1-2Ω
Rbleed (R3) = 39kΩ
VDD = 3.3V
VOUT = 1.8V
Iout = 100mA to 6A pulses at SR = 0.3A/µs
External pass device - FDB7030BL, N-MOSFET
The measured ripple voltage is 43mVpk-pk or better than
2.5%; see Figure 2.
If the potential difference between the CS and VDD
exceeds 100mV for a time greater than the value
determined by formula (1) below, the device will enter a
4% maximum on-time until the overcurrent condition is
removed.
T = C · 0.3V ÷ 36µA (1),
delay
T
where
CT is the capacitor at the CT pin.
The above applies to the initial overcurrent condition,
after which if the overcurrent condition remains in effect,
the device will repeatedly cycle on and off according to
the following formulas:
T = C ·1V ÷ 36µA (2)
ON
T
T = C · 1V ÷ 1.6µA (3)
OFF
T
During the Gate on-time, the maximum current the pass
device may supply is limited to:
2004 Semtech Corp.
6
Figure 2.
www.semtech.com
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