User guide

AP8801
500mA LED STEP-DOWN CONVERTER
AP8801
Document number: DS31765 Rev. 7 - 2
3 of 14
www.diodes.com
June 2012
© Diodes Incorporated
Recommended Operating Conditions
Symbol Parameter Min Max Unit
V
IN
Operating Input Voltage relative to GND 8.0 48.0 V
V
CTRLDC
Voltage range for 24% to 200% DC dimming relative to GND (Note 4) 0.3 2.5 V
V
CTRLL
Voltage Low for PWM dimming relative to GND 0 0.2 V
f
OSC
Maximum Switching Frequency (Note 5) — 625 kHz
T
A
Ambient Temperature Range -40 +105 ºC
Duty Cycle Using Inductor ≥ 100µH (Note 6) 0.10 0.95 —
Notes: 4. For 100% brightness either leave floating or connect to 1.25V relative to GND.
5. AP8801 will operate at higher frequencies but accuracy will be affected due to propagation delays.
6. For most applications the LED current will be within 8% over the duty cycle range specified. Duty cycle accuracy is also dependent on
propagation delay. Smaller size inductors can be used but LED current accuracy may be greater than 8% at extremes of duty cycle. This is most
noticeable at low duty cycles (less than 0.1) or when the input voltage is high and only one LED is being driven.
Electrical Characteristics (T
A
= 25°C, V
IN
= 24V; unless otherwise specified.)
Symbol Parameter Conditions Min Typ Max Unit
I
OUT
Continuous switch current (Note 7) — — 500 mA
I
Q
Quiescent Current — 78 120 μA
V
THD
Internal Threshold Voltage 184 200 216 mV
V
SENSEHYS
Sense threshold hysteresis — 15 — %
V
REF
Internal Reference Voltage — 1.25 — V
SET SET pin input current
V
SET
= V
IN
-0.2
— 7 — μA
R
DS(ON)
On Resistance of MOSFET
I
SW
= 0.4A
— 0.70 1.15 Ω
I
SW_LEAKAGE
Switch leakage current — — 8 μA
θ
JA
Thermal Resistance Junction-to-Ambient
SO-8 (Note 8) — 88 — °C/W
MSOP-8 (Note 8) — 128 — °C/W
θ
JC
Thermal Resistance Junction-to-Case
SO-8 (Note 8) — 58 — °C/W
MSOP-8 (Note 8) — 90 — °C/W
Notes: 7. Refer to figure 6 for the device derating curve.
8. Test condition for SO-8 and MSOP-8: Device mounted on FR-4 PCB, 2”x2”, 2oz copper, minimum recommended pad layout on top layer and
thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed.