AAT3183_08 Datasheet, PDF (12/15 Pages) Advanced Analogic Technologies – 300mA Inductorless Step-Down Converter

ChargePump^TM
PRODUCT DATASHEET
AAT3183
300mA Inductorless Step-Down Converter
Input
Capacitor
Size
0402
0603
C_IN
(µF/V)
2.2/6.3
4.7/6.3
Output
Capacitor
Size
0603
0603
C_OUT
(µF/V)
2.2/6.3
4.7/6.3
Input [1µF(min)]
and Flying
Capacitors Size
0402
0402
C_FLY
(µF/V)
0.47/10
1/10
Table 1: AAT3183 Capacitor Size Selection Chart
(see Table 2 for corresponding manufacturer part numbers).
Maximum
Output Current
I_OUT (mA)
220
300
C_IN/C_OUT
Value
2.2µF
4.7µF
2.2µF
4.7µF
2.2µF
4.7µF
Input and Output Capacitors
Voltage
(size)
16V (0603)
10V (0603)
16V (0603)
6.3V (0603)
16V (0603)
10V (0603)
Mfg
TDK
TDK
Murata
Murata
Taiyo-Yuden
Taiyo-Yuden
Part Number
C1608X5R1C225K
C1608X5R1A475K
GRM188R61C225K
GRM188R60J475K
EMK107BJ225KA
LMK107BJ475KA
Input [1µF(min)] and Flying Capacitors
C_FLY
Value
0.47µF
1µF
0.47µF
1µF
0.47µF
1µF
Voltage
(size)
10V (0402)
10V (0402)
10V (0402)
10V (0402)
10V (0402)
16V (0603)
Mfg
TDK
TDK
Murata
Murata
Taiyo-Yuden
Taiyo-Yuden
Part Number
C1005X5R1A474K
C1005X5R1A105K
GRM155R61A474K
GRM155R61A105K
LMK105BJ474KV
EMK107BJ105KA
Table 2: Ceramic Capacitors for the 300mA AAT3183 Step-Down Charge Pump Converter.
Input and Output Voltage Ripple:
Charge Pump Operation
The AAT3183 minimizes switching noise with PFM con-
trol. PFM switches only when required to maintain the
output load, reducing the total switching noise. PFM con-
trol generates a small amount of V_IN and V_OUT regulation
ripple (ΔV_PFM) due to the charge and discharge of the
input and output capacitors. Additional voltage ripple is
due to the parasitic resistance and inductance distribut-
ed on circuit traces and within the input, fly, and output
capacitors themselves; see Figure 3 for the graphic illus-
tration of the AC parasitic components of a AAT3183
typical application circuit.
During the charge pump switching events, an AC current
path (I_AC) is established from the voltage source (V_IN)
and input capacitor (C_IN) through the flying capacitor
(C_FLY) to the output capacitor (C_OUT) and returning
through the ground plane (GND).
The AC voltage ripple signal is measured across C_IN and
C_OUT and is highest at full load and high V_IN. These AC
currents charge and discharge the flying capacitor and
flow through the ESR and ESL, which are parasitic ele-
ments within the capacitors. Circuit board traces can add
to ESR and ESL and will contribute to the AC voltage
ripple. Proper component selection and good layout
practice are critical in providing low ripple, low EMI per-
formance. These parasitic elements should be minimized
to optimize loop transient response and achieve stable
operation.
The I_AC current from the flying capacitor flows through
parasitic ESR and ESL. Voltage ripple across the input and
output capacitors due to ESR and ESL are approximated:
∆V_ESR = ESR_TOT · I_AC
∆V_ESL
=
(ESL_TOT · I_AC)
∆t_RISE-FALL
The total AC voltage ripple (V_RIPPLE) is the sum of the
individual AC voltage ripple signals.
V_RIPPLE = ∆V_ESR + ∆V_ESL + ∆V_PFM
Due to fast switching, a large amount of AC switching
noise due to the parasitic ESL within the C_IN and C_OUT
ceramic capacitors is seen on the output ripple. This
noise may be attenuated with a small amount of input
and output filtering.
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