MP24830 Datasheet, PDF (10/15 Pages) Monolithic Power Systems – 4.5V . 90V, Programmable Frequency White LED Driver

MP24830 — 4.5V–90V, PROGRAMABLE FREQUENCY WHITE LED DRIVER
APPLICATION INFORMATION
The MP24830 can be used in buck mode and
buck-boost mode applications.
Setting the LED Current
An external resistor R_FB sets the maximum LED
current as per the equation:
R_FB

0.2V
I_LED
Setting the Switching Frequency
The switching frequency is set by an external
resistor, R_SET, connected from the RSET pin to
VSS The relationship between the switching
frequency and the programming resister is as
per the following table and shown in Figure 3.
Table 1 R_SET and f_SW Relationship
f_SW (kHz) R_SET (kΩ)
100
200
125
165
210
100
400
50.4
600
30.3
800
19.9
1000
13.2
350
Open
Switching Frequency vs.
RSET
1200
1000
800
600
400
200
0
0 50 100 150 200 250
Figure 3: Switching Frequency vs. R_SET
The MP24380 implements current mode control
by sensing the inductor current through a
current sensing resistor R_CS, as calculated by:
R_CS

0.9  V_CL
I_{L _ PK _ Max}
Where the V_CL is the current limit, V_CL=50mV,
and I_{L_PK_Max} is the maximum peak current in the
inductor.
Calculate R_CS using the minimum input voltage,
the maximum output voltage and the maximum
output current.
Setting the Over-Voltage Protection
The MP24380 detects output over-voltage via
the OVP pin. The OVP pin monitors the output
voltage through a voltage divider (R_OVP1 and
R_OVP2): When the OVP voltage exceeds 1.24V,
the IC triggers OVP.
Select the resistor value ratio using the
following equation:
R_OVP1
R_OVP2

V_{OUT _ OVP}
V_{th _ OVP}
1
The OVP trip-point is set between 0.4V and
1.24V.
Setting the Compensation
The MP24830 implements current-mode control
to regulate the LED current feedback through
the compensation network on the COMP pin.
For most applications, use an RCC
compensation network to ensure current
accuracy and the system stability, as shown in
Figure 4.
Its DC gain is:
DCGain _ EA

gm  R_FB
C_z  C_p
Where gm is error amplifier’s transconductance
of 80µA/V.
The zero of the compensation network is:
f_{z _ EA}

1
2  R_COMP  C_z
The pole of the compensation network is:
f_{p _ EA}

1
2

R_COMP

C_z
C_z


C_p
C_p
MP24830 Rev. 1.0
www.MonolithicPower.com
10
10/30/2013
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