Datasheet

charging FLY CFLY
discharging discharge LO AD(MAX)
Q = c v = C V ,
T
Q = i t = 2 I , half duty.
2
´ ´ D
æ ö
´ ´ ´
ç ÷
è ø
(1)
Both equation should be same,
LOAD(MAX) FLY CFLY
T
2 I = C V
2
æ ö
\ ´ ´ ´ D
ç ÷
è ø
æ ö
´ ´
ç ÷
è ø
\ ³
D D ´ ¦
LOAD(MAX)
LOAD(MAX)
FLY
CFLY CFLY
T
2 I
I
2
C =
V V
(2)
( )
= + ´
´ ´
LOAD(MAX)
OUT(RIPPLE) LOAD(MAX) COUT
OUT
I
V 2I ESR
2 f C
(3)
´
´ ´ = ´
´
OUT OUT
IN OUT Q
IN IN
V I
PD(out)
Efficiency(%) = 100 = 100 , I 2 I + I
PD(in) V I
(4)
( )
OUT
IN OUT
IN
V
Efficiency(%) = × 100 I = 2 I Quiescent current was neglected.
2 × V
´
(5)
PCB LAYOUT
TPS60151
SLVSA02 – SEPTEMBER 2009 ......................................................................................................................................................................................... www.ti.com
If I
LOAD
= 140 mA, f = 1.5MHZ, and Δ V
CFLY
= 100mV, the minimum value of the flying capacitor should be 1 µ F.
Output capacitance, C
OUT
, is also strongly related to output ripple voltage and loop stability,
The minimum output capacitance for all output levels is 2.2 µ F due to control stability. Larger ceramic capacitors
or low ESR capacitors can be used to lower the output ripple voltage.
Suggested Capacitors (Input / Output / Flying Capacitor)
Dielectric Rated
Manufacturer Part Number Value Tolerance Package Size
Material Working Voltage
4.7 µ F
X7R 6.3V
2.2 µ F
The efficiency of the charge pump regulator varies with the output voltage, the applied input voltage and the load
current.
The approximate efficiency in normal operating mode is given by:
Large transient currents flow in the VIN, VOUT, and GND traces. To minimize both input and output ripple, keep
the capacitors as close as possible to the regulator using short, direct circuit traces.
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