# DCDC converter output power

#### Rajinder

Jan 30, 2016
557
Hi all,
I have an application described below.

12V from car battery going to Buck DCDC converter (LM53600) to generate 5V. 5V from DCDC output feeds into LDO which generates 3V3 (MCP1826) This 3V3 powers the Micro, Bluetooth and WiFi devices.

To simulate current of 0.5A, I put a 5R load across the 3V3 output (as the WiFi Bluetooth prototype is still being built). The WiFi can peak to around 0.5A from the datasheet. With 5R load across the 3V3 output I should be getting 0.66A.

The 12V from the car battery will not drop to say 5V. It will remain around 12V, the spec is that the circuitry should operate with a car battery voltage of 9V minimum.
So my question is why I can't draw 0.66A with a 12V input, as I see only 280mA being drawn at the 3V3 output, when it should be 0.66A. is there something wrong with the circuit?

I have noticed, when I reduce the 12V input to say 5V, then I draw the 0.66A from the 3V3 output.

Is is something to do with power conversion? Or is there some basic information that Is do not understand?

#### kellys_eye

Jun 25, 2010
5,472
Where are you measuring the current draw?

#### Rajinder

Jan 30, 2016
557
Where are you measuring the current draw?
From the 3V3 LDO output.

#### Martaine2005

May 12, 2015
4,531
The LM53600 will work without the MCP1826 according to the data sheet.
Vin min 3.5V
Vout min 3.3V
Iout max 0.65A

Martin

#### Rajinder

Jan 30, 2016
557
The LM53600 will work without the MCP1826 according to the data sheet.
Vin min 3.5V
Vout min 3.3V
Iout max 0.65A

Martin
Hi
I did look at this option. However we need 5V to power some external circuitry, hence the 3V3 LDO was used.
Thanks

#### kellys_eye

Jun 25, 2010
5,472
If you have 3.3V out and an accurate load resistor then Ohms' Law can't be defeated. One or the other Volts or ohms) is wrong or your meter is.

Replies
3
Views
845
B
Replies
3
Views
998
B
T
Replies
12
Views
1K
Terry Given
T
Replies
3
Views
730
M
Replies
7
Views
892
Paul E. Schoen
P